4.236 Initial Overheat - Plumbing ?

[Fluenta]

The engine - a Perkins 4.236 - will briefly overheat if it is not left to idle for a very long time. Once it is brought down to temperature it will not overheat again even if you drive around at WOT.

Thought it was a sticky thermostat but that tested fine.

All the usual things have been checked or overhauled: heat exchanger, exhaust elbow, water pump">raw water pump. Tons of water flow out the exhaust.

Confirmed it is not an indication issue but checking with an handheld heat sensor.

One thing I did notice is that the plumbing for the hot water heater is different from another 4.236 I saw. Both sides are plumbed off close to the thermostat. How are they plumbed in on other boats ?

[Cheechako]

By "briefly overheaat", do you mean the gauge shoots up high, but then comes back down? How did you check the t stat? are you sure it's not opening too slow or too high a temp?

[Fluenta]

Yes, the engine will continue past 180 to overheat. I then bring the throttle back to idle and the temp gradually returns down to normal. After that the engine will not overtemp no matter what I do.

The thermostat was tested but not replaced (as I had requested). It tested fine but we will replace it anyway as intentions are to head across the South Pacific next year.

Thanks for the quick reply

[Cheechako]

Yeah.... it's hard to figure anything but the stat. Has it just started or been like this? It's possible the stat is fine, but the engine heat continues to soak through the engine after it opens up, showing a temporary rise in temp..... kinda like they say when you turn a car engine off it gets hotter for a few minutes....

[Fluenta]

It has always been like that for us - we have been operating the boat for just over a year. Am hoping to hear from other 4.236 users to see if this an anomaly for 4.236's or just us.

[Cheechako]

I had a 236 about 4 years ago. I dont remember it doing that, but frankly, I start the engine, look for exhaust water and usually get busy with lines, fenders, storing stuff etc.... only checking the temp after several minutes.... so I'm not sure... water heaters do get air locks in them I hear.... is the heater location above or below the engine? Not sure how that would do what you are experiencing though...

[Fluenta]

Water heater is slightly above the engine

[HappyMdRSailor]

I definitely vote for the T-stat!

Functioning in a pot of static water is light years away from the turbulent flow that they see in an engine... The "blocking plate" needs to ride up the shaft, and it seems like pressure from water flow could "cock" it enough to jam slightly until your pressure doe to pump flow is reduced when you drop to idle... Definitely could be compounded by your heater plumbing... i.e. adding more back pressure...

I've seen lots, but this would be a new one to me...

Report back when you have the answer!!!

[Fluenta]

Searched online before but missed this the last time. From the Whitby 42 users group:

"Lew-

Have a overheat problem with the Perkins 4236 on my Brewer (Hull #268). Have about 5000 engine hours. My exhaust elbow was getting clogged with mineral deposits, so I just finished a fairly extensive maintenance process where I changed out the exhaust elbow, installed a new exhaust manifold, replaced all hoses, replaced the raw water impeller, installed new belts, installed new thermostat and coolant, and acid washed the heat exchanger. Have gone over both the raw water and fresh water circuits pretty thoroughly. I have excellent raw water output from the exhaust now and the header tank coolant remains at the full level (not losing coolant). When I run the engine under load, engine temp will slowly rise for about 15 minutes until the overtemp alarm sounds (temp indicator shows under 180 degrees). I back off the throttle to idle and let it run for around around a minute or two and then then thermostat will kick in and water temp goes to 160 degrees (currently have a 160 degree thermostat installed) and the overtemp alarm will die out. I can then run the engine for hours at full load and the engine will never show an overheat condition again. But if I turn the engine off and let the engine cool down, the overheat process will occur again until I idle for a couple of minutes, etc. This happens every time.... have duplicated it around 10 times now.

So... it seems like the themostat is not kicking in soon enough to prevent an overtemp alarm. I have tried another 160 degree thermostat- same results. I have monitored the engine temps with an IR themometer. It seems that the rear of the engine is hotter than the front of the engine by 10-20 degrees. I think the overtemp alarm sender is at the rear and the engine temp gauge sender is at the front (not 100% sure of this as I haven't traced out the wiring yet).

Maybe I have air in the freshwater system ? If so, not sure how to check this or bleed it out.
Maybe I have some blockage in the freshwater system ? If so, not sure how to check this and remove the blockage.

Any ideas would be greatly appreciated, Lew.

Thanks,

Lee Davis
S/V Head Out"

Sounds just like mine except I have a 180 degree thermostat.

Some responses:


"Hi Lee,
It seems that your thermostat just needs to get in contact with the hot coolant to start it's regulation. Try drilling a 1/16 hole in the thermostat base to allow a tiny bit of coolant to bypass the thermostat. A hole this size will not prevent the thermostat from allowing the Perkins to come up to operating temperature, but would allow sufficient flow of coolant to come in contact with the thermostat itself.
Bob Slais"

"
Nice that the problem is not intermittent at least.
Sounds like you have an air bubble in the fresh water side. I would suggest a coolant over flow bottle to give the air a place to go and not come back into the system. Make certain to change the cap also so that you have a seal at the top of the cap so the coolant will go into the bottle. I will usually mount the bottle above the engine in a very convient place to be able to see it and add coolant. If you are using pre mix coolant make sure it is for diesel engines. If you are mixing the coolant yourself use distilled water and never use different colors of coolant with each other as this can lead to a gelling situation
You should be using a 180 degree thermostat to help with getting rid of condensation in the crankcase.
Apparently you have reconnected all of your cooling lines correctly or the condition would never go away. Drilling a very small hole in the thermostat is a good idea in fact some of the Perkins came with that done to their original stat.
Make certain that the stat is installed in the right direction that would be the temp sensor side in the coolant and the cone up.
Lew"

"
Guys, I have a Perkins 4.236 in hull #2. I rebuilt the engine and t does the same thing. I checked the engine with an IR thermometer and the rear is a bit warmer than the front. The thermostat is all the way in the front, the meter sender in the rear . My engine does not have an overheat sensor but the temp gauge slowly goes to about 210 and stays there. After about 5 minutes the thermostat opens, the temp comes down to 180 and stays there. I like the idea of drilling the thermostat but wouldn't go to any further trouble to resolve this. It has been completely predictable in its response over about 700 miles of operation.

John Meskauskas S/V Laume II"

Of course, there is no post on whether the recommended fixes solved the problem.

Thoughts before I start drilling holes ?

Thanks,

Max

[Cheechako]

I see no problem with drilling the small hole in the Tstat. I have seen Tstats with the hole before. It can help eliminate an air lock issue also. From reading it sounds to me like the 236 just operates that way... would be nice to check if the temp sender and the other sender are separated front/rear as indicated in the posts. You may have a non issue really. As I mentioned earlier, the heat may be soaking through the block and showing a hot spot aft even after the Tstat is open...
We fought overheating on the Yanmar in the HC38 half the way back from Trini to FL until finally discovered it was the sender and we wernt overheating at all. (didnt have the digi temp unit back then)

[HappyMdRSailor]

I second Mr. Cheech on being OK to drill the hole.... Sounds good!

[Cheechako]

Just as an example: when I rebuilt the head on my 4-108 after assembly I ran the engine and it overheated immediately. I wracked my brain and couldnt figure out what the problem was. I removed the Tstat and all was good. I put it back in and had the same issue. I removed it again and filled the block with coolant to overflowing the Tstat housing.... all was fine. Bottom line: a small air pocket under the tstat kept the tstat from acquiring the heat in the block....so it didnt open. WIsh I had known about the tiny hole trick back then!

[a64pilot]

It's not a Marine engine but later model GM engines in cars will do just this exact thing if they are not completely bled of air from their cooling systems. They are "reverse flow" cooling systems, have an air bleed right on top of the T stat housing. In short an air bubble can air lock your cooling system and do exactly what you have. Eventually the air bubble seems to work itself out it you have an expansion tank, even if nothing is done, you know when the bubble works itself out because the level in the expansion tank suddenly drops when you have no leak, obviously air came out and coolant was sucked back in when the engine cooled.
Drilling a hole in the T stat is real simple to do, a T stat is a cheap and easy to replace part anyhow if somehow this causes problems, and this hole is likely to fix your problem. If you don't have an expansion tank, I would recommend fitting one as it's easy and cheap, allows you to check coolant level at a glance and has other advantages.

[HappyMdRSailor]

Originally Posted by a64pilot

It's not a Marine engine but later model GM engines in cars will do just this exact thing if they are not completely bled of air from their cooling systems. They are "reverse flow" cooling systems, have an air bleed right on top of the T stat housing. In short an air bubble can air lock your cooling system and do exactly what you have. Eventually the air bubble seems to work itself out it you have an expansion tank, even if nothing is done, you know when the bubble works itself out because the level in the expansion tank suddenly drops when you have no leak, obviously air came out and coolant was sucked back in when the engine cooled.
Drilling a hole in the T stat is real simple to do, a T stat is a cheap and easy to replace part anyhow if somehow this causes problems, and this hole is likely to fix your problem. If you don't have an expansion tank, I would recommend fitting one as it's easy and cheap, allows you to check coolant level at a glance and has other advantages.

Great post Mr. Pilot!

[perchance]

Some engines will "heat soak" after shut down after being run. Many engines require an idle period to allow heat build up to dissipate before shut down.