Ever-Popular Overheating Perkins 4108

[jlogan]

I've been working on what seems to be an overheating problem in my 1979 4108 in a 37 Gulfstar for about a year now. So far...removed and acid washed heat exchanger, new coolant, new impeller. Engine seems to want to run at 190 F instead of 180 F, no matter what the RPM (within reason). The water coming out of the exhaust is barely warm when the boat is up to the 190 operating temperature. I don't think I have any head gasket or transmission oil cooler problems as there are no symptoms (disappearing coolant, oil in coolant, overheating beyond 190/200f, etc.)...by the way, the boat seems to have had this problem since I bought it...tested in January, no problem, water getting warmer, problem...

2 Questions on which I would appreciate opinons/answers.

1. How likely is it that this is just a temp guage/sender issue given that the water coming out of the exhaust is barely warm (you can hold your hand in it all day)

2. I probably will order a new raw water pump, but how does one determine if an old raw water pump is worn out? This one appears very shiney inside, the face plate is scored and worn, but the cam appears ok and has no worn ends or sharp edges like you see in a worn pump. I changed impellers, even though the old one appeared fine. Water flow looks the same...about like a wide open faucet at all times, and the usual big slug of water every other second or so, when running at 1500-1700 rpm. More rpm, more water flow, as usual...could just the worn end plate cause this sort of problem?

Not actually wanting to change pump, as we are looking at $500 or so, but can't see that rebuilding current pump is a good idea if it is worn enough to cause this problem

any ideas? This is running me nuts, usually I am a pretty fair mechanic, but I hate just changing parts without any idea of why I am changing them...

[never monday]

190 isn't overheating

if you were at 220 I'd be concerned.

[Kanani]

He's correct about 190 being OK but I've never seen a 4108 get to 190. Having said that, it may well have a 190 thermostat in it.

I would have been suspect of the sending unit and/or gage from the start.

I would put a thermometer in the coolant tank to check the temp.

The fact that the water is not hot, coming out of the exhaust, tells me that there is no problem.

BTW......don't save that old impeller for a spare. Once they've been used then dried out, they rot.

[CSY Man]

My 4-108 has always been that way: It slowly but surely overheats if ran above 2400 RPM for a while, 10 minuttes or more. Same if I run at 2600, 2800 or 3000, it just heats up faster at the higher RPMs. I have tried everything known to God and to mankind, but have not found anything "wrong". Figured it must be a design flaw with under-sized cooling hoses from the boat yard, or some such thing...Do a search on this pages and you should find plenty 4-108 threads, including my engine's over heat problems.

[nelsonsmoody]

Wow! I have the same problem and have done just about everything including changing the prop pitch on my max prop, help very little. Next will stuff ice cubes around the motor. We just live with it and watch all the time.
Good luck
Nelson

[btrayfors]

I agree that 190F isn't overheating. It's the correct temp for a 4-108.

If a 4-108 is really overheating, as mine did for several years and despite heroic efforts on my part and that of all the mechanics I could find in Tortola, there could be several causes and a couple of good solutions.

After several years of struggling with the beast, I bit the bullet and flew down to Tortola a friend and his wife. Don was the best engine mechanic I'd ever seen, and I knew he could find the problem. He did. It took him 45 minutes to find three problems, and about an hour to correct all three. After that, he said I should open her up at full power and run for awhile. We powered from Nanny Cay up to Cooper Island at full speed. No overheating. Voila. End of problems.

I remember a couple of the problems he found. One was the heat exchanger which, despite having been acid cleaned and tested still had more back pressure than did the new one I'd brought down with me. We replaced it.

A second problem, much more insidious, was the gasketing on the circulation pump. This pump had been removed, replaced with a new one, and pampered by the local mechanics. It has a thin steel plate which fits between it and the engine block. Problem is, the gaskets which fit on each side of that steel plate are not identical. The local mechanic(s) had fitted identical gaskets, thereby blocking a water port.

A third problem was a small leak in a water line on the "blind side" of the engine, near the oil cooler.

I remember, too, that I hadn't been very good about maintaining a 50/50 mix of engine coolant, in part because I seemed always to be adding water. The proper coolant mix is important both for cooling and for protecting the water jackets inside the engine from rusting.

Some years later, a hint of the former overheating problem returned and I was then convinced that the heat exchanger on the 4-108 is of only marginal capacity. So, I replaced mine with a larger one from a Perkins 4-236 as I remember. With a little ingenuity and a lot of swearing, I got it to fit more or less in the same place as the original, smaller one.

That was in May of 2000 while the boat was still in the Caribbean. Now, many thousands of sea, coastal, and inland miles later, that heat exchanger is still doing a wonderful job, and the engine runs exactly at its design temperature no matter how I load it. Touch wood.

Bill

[jlogan]

I appreciate all the replies. So what I am gathering from the replies is that the adequate flow and cool temperature of the exhaust water does mean I am probably not overheating....does anyone else with a 4108 have exhaust water cool enough to place your hand in while running, and also, does that stream of water sound about right for a properly functioning Perkins/Sherwood g65 raw water pump?

Can the worn end plate on the pump make a big difference assuming new impeller and no wear on cam?

I've just never had a cooling problem I couldn't fix with a properly functioning engine/raw water system, and I've had several diesel powered boats, so I still suspect something in this system is not right, although from the replies, it seems I am not alone.


Thanks

[marc2012]

Same boat think sail not motor sail,same eng.same temp.Mech say normal.Never checked exaust trmp but will next dingy over.Tell you like they tell me not to worry if capable of that please advise lol.

[never monday]

Originally Posted by jlogan

I've just never had a cooling problem I couldn't fix with a properly functioning engine/raw water system, and I've had several diesel powered boats, so I still suspect something in this system is not right, although from the replies, it seems I am not alone.


Thanks

it incredibly hard to fix a problem that doesn't exist.

[jlogan]

Does sound sort of stupid to worry about it....It is just that I equate unpredictabilty with unreliability, and since I have checked/replaced/redone every other system on this boat since I bought it, it bothers me that there is something going on here I can't predict, it just indicates a higher temperature sometimes and not others....so don't worry, be happy...I just need to sail and forget about it...

thanks for the input

[marc2012]

Are you cruising or day sailing?Am presetly in Ga but heading your way from Abbeville la sailed Biloxi many yrs.Will keep in mind just sail be happy.mjl

[mobetah]

jlogan,

Remember that the water coming out of your exhaust is raw water while the engine temp. is being measured from your engine coolant (probably at it's hotest point, just before it goes into your heat exchanger). The temp. between the two could vary quite a bit depending on the volume of raw water compared to the volume of coolant. If your exhaust is producing steam I would think you have a problem with your raw water side (not enough raw water through the heat exchanger). The more steam the bigger the problem. If there is no steam, I would not replace the raw water pump. Just my opinion.

Good Luck

[Randyonr3]

had a slight problem with the temp rising when I took it over 2000 rpm. changed the impeller out and still had the same problem. I did notice the plate was worn so I sanded off the paint from the front and turned it around.. solved the problem.
Something to notice. there are replacement parts for the inside of the pump and if they are worn to where the you dont have a good seal. you'll lose water flow.
All may work well at 1800 to 2000 but at the rpm rises, so does the temp.

[S/V New Sensation]

When we first bought the boat our 83 4-108 would overheat when pressed. I replaced the raw water pump (leaking) and the thermostat (just in case) no joy. I took out the heat exchanger it looked good but I cleaned it anyway and during my inspection I found a crack in the outer covering for the tube bundle. Although it didn't look large it would allow some by pass flow (i.e. the freshwater side wouldn't be completely cooled by the salt water). I had a radiator shop seal the crack (they brazed a thin piece over the crack) then put it all back together. Since then the engine does not overheat and in fact runs a little cool (new thermostat appears to be stuck ) so at least for me it was a simple fix just kinda hard to find.

[kinne]

I have a Perkins 4-107 and the same problem, overheating after running the boat on full throttle. This year I did change the prop pitch from a 15X10 to a 15x12 and now can run at higher RPM's with more speed, although still having the overheating problem at full throttle. As for wear of the raw water pump, mine has lots of wear and I am in the process of changing it out for a Sherwood G65, which I found for $349.99 plus shipping, it should be in later this week. I have put in a new heat exchanger and thermostat. That did not solve the problem. My diesel guy has told me that it is common for the Perkins 4-107/108 to overheat and he recommends a larger heat exchanger. I like the post about replacing the exchanger with a Perkins 4-236 heat exchanger.
Kinne