Heat
Exchangers & Overheating
Sailnet Tayana List
I found a
couple of sources for heat exchangers. One name I got from Harvey, Harpur
Marine in
Ray Slaninka November 2000
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I only bought the Heat Exchanger from
Harpur Marine, not a complete engine.
But you could contact them. The person I dealt with was Fred Sweers, but
anybody there will be helpful. The phone number at Harpur Marine is
310-830-0693. But from where you are, it will be one hell of a long distance
call. They are in
Another option that many people have
exercised is to put in a Yanmar. If so, you are better off with the 45 or 50 HP
not the smaller 33 HP - although many people seem quite happy with the 33 HP.
Whatever you do, according to
everyone I spoke with, DO NOT use Foley Marine on the East Coast. They have a
terrible reputation.
regards,
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I am
considering changing the MD3B Volvo to a Perkins 4108 (Sorry John but the blue
smoke is causing a small smog problem over the marina). There seems to be a few
on the market which have not been marinised which I am
considering.
Also if anyone has
details of where a complete marine kit can be purchased for a 4-108.
Bill Moloney April
2001
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The
typical heat exchange that is applied to a Universal Atomic-4 @ 3 gpm rate + 35 hp ... so the BTU exchange rate should be
similar ... albiet just a tad undersized) goes
commercially for about $350.00 @ distributor list $. I'd be pretty sure that
the manufacturer could furnish one that's 40% longer for a few extra $$$ for
the extra length tubes ... as the weighted cost of manufacture is the rolling
of the tubes into the tubesheet. The mounting could
be on a wall of the engine compartment so you'd need to do some plumbing/hose
changes, plus a few extra inserts for pencil zincs and bonding connections ..... Would save a bunch of $$$$$. You might want to alternatively check out
your local "shell and tube heat exchanger" supplier or distributor
for other economical alternatives. Ask/consider a U-tube bundle exchanger ...
usually 2/3 the price of straight tube bundle. There's no reason for a huge
cast steel headed exchanger – if you are careful with zinc anode
replacement/inspection.
Rich Hampel
April 2001
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I followed
up a thread re 4-108 heat exchangers - you mention purchasing one made in
Washington State - is the contact you gave me (swdieselinc@aol.com) a supplier for the unit you purchased ? I have been quoted US$1200 for one supplied
locally.
Regards, Bill Moloney Covenant III CT37 #34 April
2001
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$1200 for the Heat Exchanger?! I assume that you really
meant to write that this was the price in Kiwi dollars. I paid $350 for a brand
new heat exchanger (plus shipping from
Check out: http://i-netmarine.com/he/heat_exchanger-perkins4_6_cyl_models.htm
They are selling heat exchangers for
the Perkins 4-107 and 4-108 for about $2500-$300(even cheaper than I paid), and
I think that they are the same brand as the one I bought. Get the Cupro Nickel
model. It's only about $20 more, but will last longer.
These same people sell exhaust
manifolds, water lifts, etc., for very reasonable prices.
regards,
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Heat
exchangers are probably BEST cleaned by using a mixture of organic acids that
remove the carbonate scale but do not affect the base metal at all.
Commercially available products are: Marsolve & Rydlyme - commonly used to
descale heat exchangers and engine internals.
So, using one of these in your system will clean the scale from the
engine AND the heat exchanger AND the exhaust manifold all at the same time.
You can use various inorganic acids (muriatic, etc.,) but take the risk of
dissolving some of the metal. If you are
experiencing rapid and repeated scale build up, especially on
the raw water side, I strongly suggest replacing the thermostat (on ANY engine)
with one that opens at less then 145 degrees, as at below this temperature the
carbonate salts in the sea/raw water will not precipitate out onto the metal
surfaces. Its
always best to operate an engine as hot as possible to enhance combustion
efficiency; but, if you are constantly scaling it up, using a thermostat that
opens at 145 degrees will eliminate a
Rich Hampel
May 2002
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Rich, we
have a raw-water cooled 3QM30 with about 1,950 hours on it and it is starting
to scale up. I have read about Marsolve and even found their website at http://www.marsolve.com/index.html
. They recommend circulating the Marsolve for several hours through the engine.
I am reluctant to spend a lot of money on their pump system and wondered if you
had any ideas. One suggestion I've heard is to use a bucket and 12v bilge pump
to circulate the solvent through the engine and back into the bucket but it
sounds a little too Rube-Goldberg.
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A few
comments about our experience with overheating: Although you are sometimes
lucky and find that only one thing is causing the overheating, there are
usually several contributory aspects to this. It's important to work through
each of them carefully. Think of it in terms of two parallel systems: one is
the salt water intake and output components, and the second is the fresh water
circulation system. The heat exchanger sits between them. (The salt water
system includes: raw water strainer, salt water pump, heat exchanger, exhaust system.
The fresh water system is the reservoir, hoses, thermostat, and also the heat
exchanger, etc.).
1) Flush out the cooling system very thoroughly.
Even after many years of usage, people have noted that there is residual crud
from the original casting of the engine block.
2) Replace the thermostat. Use a 158-160 degree
unit. When installing, don't overdo it by putting on too much gasket sealant.
It can ooze onto the thermostat and cause it to block.
3) Replace the salt water impeller in the water pump.
4) Check all hoses, and replace if they look bad
5) Make sure that there are
no obstructions in the exhaust manifold
6) If in doubt, replace the heat exchanger. They
contain a number of narrow and fragile copper tubes. Despite repeated cleanings
by a professional shop specializing in this, the overall flow rate was
inadequate. It was only after replacing it completely that we managed to bring
the overheating under control.
7) CHANGE THE ZINC IN THE HEAT EXCHANGER!! Do this
every time you change the oil. It is easy to overlook this. It is a major
contributor to heat exchanger failures. If you have to buy one new heat
exchanger, you will never again forget to replace the zincs in the future.
8) Open the intake side of the heat exchanger to
remove any debris that might have gotten past your water intake strainer.
9) Check and clean the transmission cooler. It is
part of the system, and is easy overlooked (I refer to the Perkins system. Not
sure about the Yanmar).
10) Get an oversized raw water strainer. The flimsy
little units with port diameters barely large enough for your intake hose are
poor economy. The large Groco bronze units are not that much more expensive,
and give you an important margin of safety from all the garbage floating in our
waterways.
Remember to clean it out every time you change the
oil.
11) Check the Vetus Water-lift and all parts of the
exhaust lines from the exhaust manifold.
12) Make sure that you
carefully bleed all air from the system. Air-lock is a very common cause of
overheating. One simple solution is to put a hose and a small petcock on the
bleed valve on the top of the heat exchanger. This assumes that the heat
exchanger is at the highest point in your cooling system.
13) Be careful about trapping air or other blockage
in your hot water heater exchanger.
Some general comments on overheating –
According to the Perkins people, (don't know about
the Yanmar) they are happy between 160-180 degrees. Most diesel people I have
met prefer it to be about 180 degrees.
Put an
overheating alarm in your system. Cheap insurance, as it is all too easy to
ignore the temp gauge. (Replace any idiot lights with a real thermometer
gauge). Make sure that the gauge is
reading correctly. Don't be too
impatient when solving overheating problems. Remember, on older engines, it's a
high likelihood that there are multiple contributory factors leading to the
overheating.
regards,
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Subject: overheating on the 3QM30?
On old raw
water cooled Atomic-4s, etc. we just put in the Marsolve and let it soak for a
week or more. The recirculation recommendation is to keep the Marsolve and the
looped cooling water as hot as possible to enhance the chemical reaction time,
just takes longer to do at ambient temperature and with non-moving fluid.
You're not going to descale it all but maybe several hundred hours worth and
that's still worth it.
When in a hurry we essentially
collected the exhaust water into a bucket/tub, disconnected the inlet raw water
hose from the seacock and ran a long intake hose back to the bucket. Ran the engine (now closed loop cooling) until the water got hot
and then simply shut down. Every few hours repeated by starting,
warming, stopping.
If you're well experienced with
working with strong acids and their neutralization, there is always muriatic
acid, etc.
Rich Hampel May
2002
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I suspect that you may have air-lock
in your cooling system. Bleeding the air
from the system refers to bleeding the air from the cooling system, not from
the fresh hot water tank. In order to bleed the air from the system, you have
to find the highest point in the cooling system (containing the anti-freeze
fluid), and then let that bleed off. In order to avoid burning yourself, and to
do it in a controlled manner, I suggest the following (I have the Perkins
4-108. It may be different on other engines):
1) Get a fitting for the bleed valve on the top of the heat exchanger.
2) Connect a two-foot length of highest quality engine hot water hose.
3) Attach to the fitting on the top of the heat exchanger
4) Put a petcock for bleeding the system at the end of the hose.
5) Hold the hose vertically while the engine is running
6) Open the petcock. The anti-freeze will start to come out. Let it flow until there are no more bubbles in the system.
This may
solve your overheating problem. We struggled for two years with resulting new
salt water pump, fresh water pump, new heat exchanger, new hoses, new
thermostat, new thermometer, considered re-cutting the prop (I decided against
that!), until I finally did this simple thing for a total of about $10. It solved the problem. I now sit at a constant 174 degrees regardless
of the length of time that I run the engine. Hope this helps.
Regards,
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Chuck June 2002
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We also have a Perkins 4-108. A solid, workhorse engine. (See the recent evaluation of
engines in Practical Sailor). Not clear from your description which version of
the heat exchanger you have. You should have one intake port for salt water,
one output for salt water, one intake for the cooling fluid (antifreeze) and
one output. The heat exchanger is literally that - salt water flows in and out
in a number of parallel copper tubes. The copper tubes are surrounded by
antifreeze. The anti-freeze transfers the heat from the engine to the salt
water, hence the name Heat Exchanger. The air lock
occurs in the chamber containing the Anti-freeze fluid. The heat exchanger
should be at the highest point in your complete system (i.e. it should be
higher than your water heater).
In addition, you should have a large
diameter plate ("clean out cover") at the intake side of the
saltwater port that can be removed. Some heat exchangers have a plate at each
end. This is critical as it allows you to remove large fragments of material
that might get drawn into your saltwater intake. (I assume that you have a raw
water strainer between the through-hull and the saltwater pump - if not, you should
put one in for safety of the engine). If your
saltwater impeller deteriorates, the parts
will get caught in the heat exchanger.
In addition to those four ports, and
the clean out covers, there are two additional smaller ports on most heat
exchangers.
One, at the bottom of the heat
exchanger and closest to the saltwater intake port, is the Zinc. This is
threaded into a brass/bronze cap that screws into the heat exchanger. It MUST
be changed every few months. We routinely do that when we do an oil change.
Failure to do this will result in serious damage to the heat exchanger by
galvanic corrosion. It is hard to see, so many people
fail to attend to it.
The second and smallest port on the
heat exchanger is supposed to be in the center and on the TOP of the unit. It
might actually be possible to mount the heat exchanger upside down. If you had
a dummy car mechanic work on your boat engine, this might actually happen. This
is the bleed port, to eliminate air from the closed system containing the antifreeze.
This is under pressure, as all are familiar with the issues about removing a
"radiator" cap (Actually, it is called the reserve reservoir, since a
boat doesn't have a separate radiator). The bleed port is supposed to be at the
very highest point in the cooling system, so that air will accumulate there and
can be "bled off". This is most easily done if you add a small hose
with a petcock to this port. Trying to loosen the threaded insert, let out air,
and then force it back into the port, while scalding your hands with extremely
hot toxic fluids, in the dark, is not my idea of fun. $2-3 worth of parts solve this problem easily.
The heat exchanger is actually a
simple, but critical component of your heating system. I don't know the
statistics, but I will bet that improper bleeding of the heat exchanger is a
major source of engine overheating. I would definitely look into that long
before I started re-cutting the pitch on a propeller, changing thermostats,
temp gauges, water pumps, exhaust lines, water lifts, heat exchanger, etc.
(Needless to add, my BOAT mechanic changed all those things while trying to
figure out why I was always overheating, before I discovered the bleed port. It
was a $2,000 lesson. I realized it only by chance when a local diesel engine
mechanic asked about the bleed port and told me that he always puts on a
petcock to facilitate bleeding the engine. Since that time, my engine sits at a
steady and imperturbable 175 degrees F.
regards,
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Subject: Perkins Engine Heat Exchanger Query
I have a Perkins 4-108 and want to
make sure the "zincs" in the heat exchanger are okay. My heat
exchanger (small cylinder over aft end of engine) has 3 small plugs and one
large plug. Two of the small plugs (7/16") are near either end down low
and the third is in the middle up high.
The large plug (11/16") is on the port side near the hose
connections.
When I removed the
starboard small plug... no water. When I removed the port small plug,
fresh water came out. Obviously no water came out of the top center plug. When
I removed the large plug, salt water came out.
The small plugs are flat on the end
and the large plug is hollow with threads. Am I correct to assume that the zinc
gets screwed into the threads on the inside of the large plug? If so, are they
a standard item at West Marine type stores?
It doesn't appear the small plugs are
for zincs. Am I correct to assume so? What, then are they for?
My engine was running hot and I was
worried that the heat exchanger was blocked. Clean water came from both the
salt water and fresh water holes. How
can I tell if it is blocked and not cooling the water properly?
Thanks for any advice! I really learn
a lot from all the postings you folks make!
Bill Roberts S/V
Kracker T-37 1977
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I was
shocked at the price I have to pay for this elbow. Are you ready for this - $330 direct from
The boot which in my estimation will be trashed when I am done is $35 versus
$60 here. What I have been told is that
these engines being almost 20 years old were never imported in to the
FYI, the Perkins Elbow part number is
4133y001. They call it a
connection. The gasket is 2481886 or
2481885. They call it a joint. The boot 24865264,
they call it a cover.
Andy Windy Blue June 2002
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This is a great e-mail list! Thanks everyone for the great advice. I forgot to mention that when I removed the
heat exchanger tube stack I took it to a radiator shop to be cleaned. I
couldn't see any blockage of the tubing ID's and the outside was covered only
in slime before it was cleaned. Afterwards it was clean metal. When I
disassembled the heat exchanger, thermostat, raw water impeller, and raw water
strainer I checked thoroughly for calcium buildup and debris of any kind. I
drained the heat exchanger and engine block completely. I did not drain the hot
water heater. I filled the heat exchanger
fresh water side (with radiator cap) with new 50/50 Antifreeze water mix. I
left the radiator cap off, ran the engine, and watched the temp gage climb to
150° then the new thermostat opened. I could tell this because the thermostat
cover and heat exchanger got hot; as hot as below the thermostat and I could
see water rushing by in the open heat exchanger. I ran the engine in gear at
the dock at 2000 RPM for one hour. The temp stayed at 175° until I went for a
ride and took the engine up to 2600RPM. The temperature rose to over 200° and
the buzzer went off.
I will take "getting a different prop" off my checklist.
I will check my hot water heater for airlock.
Doug Simms Aquadesiac Tayana
V-42, #108
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I did some
research last night on line and found the Bowman web site. They made the heat
exchanger/tank/exhaust manifold casting for the engine that I have. The Perkins
service manual refers to it as the "New" Perkins 4-108.
I looked
at the i Net Marine heat
exchangers and they look like only a heat exchanger. I would have to get a
separate exhaust manifold and header tank to make theirs work. FYI: The Bowman Part number is PE180-3483 http://www.ejbowman.co.uk/products/pdf/marine.pdf . Go to page 2. The top photo is my engine.
Since they
didn't have any
Doug Aquadesiac Tayana
V-42, #108
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Doug,
The
continuing symptoms sound very much like the ones I experienced. That does not guarantee that the cause is the
same, but maybe.... Do not disconnect the return hose unless you are certain
that it is the highest point in the system. The air gets trapped at that point
and causes an airlock. Is your heat exchanger higher than the top level of the
water heater? Exactly where is your hot water heater in relationship to the
engine? You may find it helpful to completely bypass your hot water heater
until you track down and solve the overheating problem. If the heat exchanger is the highest point,
look on the top of the heat exchanger in about the center for a small brass
bolt. It has either a hex head or a square head. It is no more than about
1/4" diameter.
When the engine is cold, remove that
bolt. Go to your local friendly engine parts shop with that bolt in hand. Find
a brass fitting with the same thread (male) and a barbed outlet. Get a piece of
black engine hot water hose that fits on the barbed end. Make it at least 2
feet long. Get a few hose clamps. Now
get a small petcock that will fit on the other end of the hose. Assemble the
pieces, with hose clamps on all junctions. You may have to use and extra
fitting if the engine oil filter blocks your free access to the point of the
bleed screw. (It did on ours. I had to get an extra small right angle fitting.
It increased the cost another buck.
Thread the assembled unit back into
the hole on the top of the heat exchanger. Keep it vertical with the petcock
well above the highest point of the engine, heat exchanger, and hot water
heater. Position the petcock in a place that you can easily reach it SAFELY
while the engine is running.
Now start the engine.
Let it run at the dock for 10-15 minutes.
Very carefully - Open the petcock and see if
antifreeze flows out freely.
Try not to burn yourself on the hot antifreeze. Have
a small bucket handy to catch the flowing antifreeze. It is toxic to the
environment and should not be dumped into the harbor. This is the first stage
of bleeding. Now close the petcock.
If the engine remains cool, run the
boat around the harbor, with a sharp eye on the thermostat. After about 15-20
minutes, with the engine still running, and again being very careful not to
endanger yourself on the running engine, open the petcock once again, and let
it flow until you no longer get any bubbles coming out. Close the petcock.
Motor around the harbor a bit more, and repeat this several times.
If this is the source of the problem,
this should solve it. But it requires some persistence and repeated bleeding.
Don't be too impatient, and don't get too far from the dock, just in case this
ISN'T the source of the problem.
While you are doing all this muddling
about, you also probably stumbled upon the Zinc at the bottom of the intake end
of the heat exchanger. That Zinc should be changed with regularity.
Other things - did you change the
thermostat? That is a cheap part, and should be replaced. Make sure that you
get one that opens at about 160 degrees F. I found that the 156 degree unit
actually maintained the engine at just about 175 degrees F. This may be due to
some tortuous passages in the cooling system. In examining the original
thermostat, I found that it was all encrusted, so I replaced it with a new one.
But initially, I used too high a temp. After cleaning the original brass
thermostat, I found a calibration temperature written on it of (I think?) of
156 degrees.
It is quite simple to remove the
thermostat. If the overheating continues, try popping out the thermostat and
running the engine that way, without any thermostat. We did that and found that
the engine stayed at about 130 degrees. I never could get it any higher
(assuming that you also bleed the engine after each of these changes of
thermostat). I put the thermostat back in and found a second problem was that I
was too exuberant in my use of silicone gasket material on the thermostat. I
put a bit too much on, and it plugged up the thermostat. It only requires a
very thin film of the blue silicone gasket material.
I also assume that you thoroughly
flushed out the fresh water cooling. Crud can accumulate in the internal flow
system. Give the whole system a good flushing.
Did you also make sure that the saltwater flow is
adequate?
Did you check the salt-water strainer on the intake?
Did you check the intake through-hull port for
debris?
Do you get an adequate flow out the stern exhaust
pipe?
Are the exhaust hoses fully patent, or have they
gotten soft and old with age and partially collapsed?
How about the various engine hoses? Are they in good
condition?
Check the flow through the transmission cooler.
Change the "radiator" cap (actually, it's
called the coolant reservoir cap).
This ain't
rocket science. It is two flow systems, one cold ocean salt water, and one an
internal fresh water system. Their only interface is the heat exchanger. Check
each system, the fresh and the salt, and check the heat exchanger.
If it is of some scant consolation,
we had to screw around with our system for several months before we realized
that the major source of problem was failure to adequately bleed all the air
out of the system. A lot of mechanics seem to skip that, because the location
of the bleed screw is damned near inaccessible, and when you do try to loosen
it, it tends to fall into the deepest part of the bilge, and the hot antifreeze
burns your hands when trying to thread it back in place. The petcock is a
simple solution.
There was one really puzzling aspect
to our experience, which also resembled your experience. When we slowly started
to improve performance, I could run it at the dock for quite a while when in
gear, and the engine didn't seem to overheat. But when I was motoring around
the harbor, after about 30-45 minutes it would climb up to about 210 degrees F.
I would have thought that running the engine in gear at the dock would impose
an equivalent load as motoring. But apparently the load is not the same.
At risk of provoking the wrath of the
gods, we have not had any overheating for the past two years.
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Subject: Help, I need a Perkins
part.
My Perkins
4-108 has a nasty over-heating habit. I have replaced and checked the easy
stuff like the thermostat, the sea water impeller, and removed the copper or
bronze tube stack. I also cleaned the raw water strainer.
I noticed
a lot of corrosion at the heat exchanger casting nipple to the thermostat. I
was wondering if the internals of the heat exchanger casting have corroded
enough to not direct the flow through the tube stack. The seawater coming out
of the heat exchanger is just luke warm even though
the engine temp is +200°F. I checked
with a local Perkins diesel shop and he thinks that my prop is too big. The
engine will not turn faster than 2750 RPM in gear. Does anyone have any
experience with the heat exchangers corroding away? I did see several similar
vintage Perkins engines with new heat exchangers on the internet when I did a
search.
The quoted
cost for the Perkins heat exchanger was $1800.00 and a Bowman unit was only
$1100.00 (cheap). The units at the i Net Marine site don't look
anything like the combo exhaust manifold/heat exchanger unit on my engine.
Doug Aquadesiac Tayana
V-42, #108
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I'm
experiencing exactly the same problem with our 4-108. Have gone through all the procedures you
have. Temp gauge goes into the red if run for any length of time under load at
2500 RPM or over. Two mechanics have looked at it with no ideas that have
worked. If I run up to about 2400
everything is fine, but still running hotter than thermostat is set for. Around 2200, will stay at 180 continuously. Any ideas out there?
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Subject: Overheating at higher RPM,
but not at lower?
Hi Harvey:
Thanks for
the suggestion, but the mechanic at our yard did check the revs last year and
the tach was petty close.
We have a
17" Max prop which I've adjusted three times, including a shallow pitch
(can't remember how shallow I went) where I wasn't able to power much over
about 4.5 knots (changed that one after about 4 miles of motoring). The
overheating problem hasn't seemed to be affected much by my pitch changes, more
by the RPM.
We've
replaced the raw water impeller. We've pulled and cleaned the exchanger. We've
changed hoses. I even replaced the water heater (but for different reasons -
the 10-year old one we inherited started leaking). Checked the actual engine
temp with a gun to ensure that the gauges were reading right -- they are. The
overheating remains.
BTW -
we're also not very happy with speed under power, which is a function too of
RPM’s that I can run without overheating. In flat water, I can only run somewhere
between 5.6 & 5.8, which is what I easily did on our Van32. Seems like the 42 ought to easily power between 6.5 & 7.
On that front, I had about come to the conclusion that the Van 42 needs about
75 horses -- that the 50 horse Perkins is just not enough, but maybe I'd feel
differently if I could run the revs up a bit more.
Bill Rohde
June 2002
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Hi Folks,
I had the same problem with a V-42 and a 4-108. I did everything I could with the water system, heat exchanger, prop pitch (16 inches fixed, changed it from 11 to 10 and then to 12 to see what difference it would make), etc and got the same result - couldn't go over 2200 rpm without overheating and at that RPM could barely get 6 knots and much less than that with any kind of head wind. I talked to one guy who bought a second heat exchanger and installed it in parallel with the first and that solved his problem. But I came to the same conclusion as Bill - a fifty horse motor is not enough - especially one that develops its fifty horses at almost 4000 RPM. Its too noisy and vibratey at anything near that speed and it seems as if it would wear out quicker because it has to run at such high revs. At the 22-2400 RPM range we have been talking about that engine only is putting out about 30 horses. So I changed out the engine (in process) to a Perkins-Sabre M65 (same footprint) which develops 65 horses at 2400 RPM. This will allow me to run a serious alternator (250 amp) at very low RPM as well as develop enough horses at lower RPM to push the boat along at something approaching hull speed using a bigger prop. I'll let you know the results.
John B. Van Zwieten
July 2002
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Hi V-42 Owners,
I have
solved my overheating problem by adding a second heat exchanger. I will post
pictures on my web site in a few weeks. I had already received the replacement
Bowman unit and I am running out of time before my trip, so I used it rather
than order a different type.
I spoke to
the Technical Expert at Bowman about the capacity of the PE180-3483 heat
exchanger. He said that the heat exchanger was designed to get rid of 50
horsepower equivalent in heat. As I remember my physics of the Diesel engine
from school, a diesel is efficient, but not 50% efficient. The Perkins consumes
3.6 gallons of diesel per hour at 4000 RPM and full throttle and diesel has a
heat content of 145,000 BTU/Gal. That totals 522,000 BTU/hr or 205 horsepower.
Since the engine's output at 4000 RPM is 51 horsepower, that
leaves 154 horsepower or 392,000 BTU/hr to get rid of in heat (by the second
law of thermodynamics, conservation of energy).
I put the
second one in series in stead of parallel because the sea water was still cool
coming out of the original heat exchanger.
I also noted that the water routing on the heat exchanger was set up for
parallel-flow rather than counter-flow. What I mean by counter-flow is the cold
seawater should enter the same end of the exchanger as the fresh water exit.
Heat exchangers are more efficient with counter-flow routing so I re-routed
mine to counter-flow. I used just fresh water only to check for leaks and the
engine would run at 150°F for 45 minutes at 2600RPM in gear. Bowman used aluminum
for the casting touting it as "corrosion resistant". Nothing could be
farther from the truth in the marine environment. Aluminum is right next to
zinc in the galvanic table so the aluminum casting will disappear just like
zincs do. I used a 3/1 antifreeze/water mixture in the freshwater side to
reduce the corrosion of the aluminum. With the antifreeze coolant, the
temperature stabilized at 175°F after about 30 minutes at 2650RPM underway.
Since the water temperature was 64° this indicates to me that 2 heat exchangers
are still marginal when you use antifreeze.
I was able
to get 6.8 knots @ 2650RPM going into 10 knots of wind and 7.2 knots at 2750RPM
going with the wind. I have to agree
with John that the Perkins 4-108 is probably too small for the V-42.
Doug Aquadesiac Tayana
V-42, #108
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My tach
(as I believe most diesels do) comes off the tach. Also, I can only get 2200
RPM indicated on mine at full throttle, so am not sure I trust it until I can
find an optical tach to borrow sometime so I can verify it.
By the way, for anyone concerned with
the overheating issue, I solved mine. The symptom was that it would run fine for
10-60 minutes, then overheat (faster at higher
throttle than at lower). I pulled my heat exchanger, filled it up with Lime
Away (purchased at the local Longs drug store) and left it over night. By
morning, the foaming had stopped and there was 1/4" - 3/8" of what I
think was calcium carbonate sludge in the bottom of the bucket. But it back
together and now I can't get it to overheat even at full throttle.
For the record, removing and
replacing it was not as difficult a job as I had feared.
Fair winds - Dan Best September 2002
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Dan,
The Perkins 4-108 has two methods for
reading engine RPM. The major and most common method is that described by Dan
Best. It is a direct take-off from the alternator. The second method is a
mechanical take-off near the forward end of the engine on the starboard side.
It is a small 1.5" cap just above the engine sump. It requires a special
gauge, and I have never actually seen one in operation.
The output from the alternator to the
Tachometer is determined by the size of the pulley on the alternator. If you
change the alternator from the undersized Delco-Remy originally provided, make
sure that they put on the correct diameter pulley drum. If you have the typical
Tachometer from Teleflex commonly provided with Perkins engines, you will find
two adjustments on the back of the meter. A large black one
with a screwdriver slot and with a pointer to A, B and C. It will
probably be pointing to C. These
selections refer to the settings required for each of several different
diameter pulleys (and alternators?). This sets the general range. But you also have to get an external optical
tachometer to fine-tune the calibration. There is a smaller hole up and to the
left of the adjustment
screw mentioned above. It requires a fine jeweler's screwdriver.
Using an optical tachometer, (a small
strobe, a piece of reflective tape on the main drive of the engine and a
digital multimeter), and extreme caution not to get too close to the spinning
engine, generate a performance curve for your engine. This generally requires
two people. Take a reading of the tachometer in the cockpit at different RPM’s
from about 500 to 2,500, while also reading the values on the optical
tachometer. This will provide you with a calibration curve for the tachometer/
alternator combination. If the values are less than 5% apart at all RPM’s, you
should leave it alone, and be happy. In our case, they were off by slightly
over 20%. Using the small jeweler's screwdriver, adjust the small screw visible
through the small hole in the back of the Tachometer. This only seems to bring
the range into approximate value, and I have to check it further, but I have
the impression that it changes the offset value uniformly across the full
range, rather than changing the percentage. (i.e. it
will add 300 RPM across the full range, rather than subtracting 20% - that is,
increasing the reading at 500 to a new value of 600, while increasing the value
of 2,000 to a new value of 2,400. Instead, if you increase the reading at 2,000
to 2,400, it will increase the reading at 500 to a new value of 900. ) If this
is true, (and I think it is), I decided to increase the reading for the high RPM
for maximal accuracy to avoid over-revving the engine. Hope this helps.
regards,
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By moving
the water heater out of the heat exchanger loop our boat realized a 15%
increase in the top, continuous speed. The following web page shows three
graphs of the engine temperature versus boat speed. The first is the original
condition, the second with new raw water pump, and third is with the water
heater moved to the thermostat by pass.
www.sankaty.homestead.com/speed.html
I am happy because our good old 1980, 32 HP, Universal 5432 no longer
overheats.
Markus Ritter October
2002
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My 3QM30H
with raw water cooling (i.e. no heat exchanger) runs at 170 degrees at cruise
RPM. This seems too hot. Don't want the salt to come out of solution and clog
engine cooling passages. What temp do others see for this setup?
Kendall Bailey October
2004
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A rise in
temperature causes a corresponding rise in the ability of water to hold any
given concentration of salt, i.e., hot water can hold more salt than cold
water.
Voyager October 2004
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Change to
a thermostat that opens full at 135 degrees to lessen precipitation of
carbonates.
Even with a 135 degree thermostat
there will be zones inside the engine (exhaust manifold & head) that will
exceed 150 degrees; 150 degrees is the point where carbonates begin to drop out
of the seawater and adhere to the internal passages.
Plan to 'pickle' the engine yearly
with an organic 'descaler' such as RydLyme® or Marsolve®. Try not to use an
inorganic acid such as muriatic, etc. as they will also remove base metal.
Rich Hampel October 2004
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Best
advice I can offer versus 'over-heating problems' is to take a bucket and
stopwatch and go to the exhaust port at the stern, run the engine at a
specified rpm (as per your manual) and see if the
flow rate (gallons per minute per rpm level) matches the spec. The cooling
water flow spec should be something like: 4 gpm @
2000 rpm, etc. If you don’t have the spec. flow rate coming out the back end,
then look for obstructions: broken pieces of impeller, the exhaust manifold
starting to degrade internally (can give 'transitory' problems), etc.
If the
flow rate matches spec. then you have a 'fouling problem" or an air
blockage .... and it may be 'in the engine' (need for
'pickling') instead of the exchanger (unless you filled with distilled water)
etc. If all that investigation fails to find the culprit, then ask yourself if
the engine is overfueling (high-pressure pump) or is the engine 'lugging' (high
load + low rpm --- wrong prop pitch).
Exhaust manifolds are cast iron and
although a good metal for such service, sometimes degrade by having huge rust
'platelets' of rust break loose from the internal walls and temporarily block
the flow passages (they also form pin holes and leak water into the combustion
chambers and ruin the engine .... lets not go there). Next time you have an
overheat problem, quickly and without burning your hand simply and quickly run
your hand over the engine and the exhaust circuit seeking the 'hot' spot. You
don’t have to actually touch the engine, just get close enough to feel the heat
radiation. Compare when the engine is
running 'normally'. An alternative is to go to a dairy supply and get '
Rich Hampel
May 2005
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Subject: Overheating Perkins 4-108
Thanks for
the responses. I am deeper into engines than I have ever been before. A couple
of questions for you, collectively:
What is pickling my engine. I can grasp the thought - something like cleaning
the head with vinegar - can I do that?
What type of petcock do I use? Would
it be available at an automotive store? Would I install it on the forward side
of the heat exchanger?
If any of you have a 4.108, where is
the drain for the cooling system. The best we could do
was disconnect the lower hose on the heat exchanger
(feed line) for the water heater.
If any of you have a T-42, what size
prop do you have? Thanks.
Jon
May 2005
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Hi Jon,
Hope you can track down the overheating
problem.
A "New" Perkins 4-108 (Bowman heat exchanger) passes 5 gal/min
of water through the exhaust system at idle (700-750 RPM). I conducted this
test on my boat with a properly functioning cooling system. Pictures
of most standard models are at ftp://tognews.com/Perkins_4_108_Models
. The “New” was the last model
built. Models built previous to that
engine are often called “Lowline” or “Highline” engines due to heat exchanger
configuration. It sounds like you
have one of the older models with a different cooling system. It should be as
good if not better than the Bowman setup, which is a little undersized for a
Perkins if everything is not ideal.
Has your boat been in the water for a
year now with no bottom cleaning? Fouling can cause sluggishness. And it can
happen quickly. I once stayed two days
in a marina and lost half a knot (at cruising RPM). That evening, I cleaned the
bottom and gained all that speed back. It was just a light coat of slime. I
wouldn’t have thought fouling could occur that quickly or cause such a dramatic
drop in speed.
Wayne V-42 C/C RESTLESS
May 2005
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