overheating engine

GeorgeH · Post by **GeorgeH** » Sep 5th, '11, 19:43

Any advice on what I can do, other than the obvious, to stop my 27 year old Volvo diesel from running in the red. Saturday, pushing against an incoming tide, the engine continually went into the red heat zone until the thermostat opened and brought it down to green. It continued to do that repeatedly as the engine was under load. Other than that the engine runs fine, it starts easily, with little smoke and sufficient water out of the hull.

trapper · Post by **trapper** » Sep 5th, '11, 20:24

Dont know about your volvo. We replaced the impeller on our yanmar and it worked. Good luck.

Duncan · Post by **Duncan** » Sep 5th, '11, 20:28

GeorgeH wrote:... the engine continually went into the red heat zone until the thermostat opened and brought it down to green...

This sounds like the issue could be a sticky thermostat.

Oswego John · Post by **Oswego John** » Sep 5th, '11, 21:05

Remove the thermometer and place it in a pot of water and heat it on the stove. Place a candy or other immersion type thermometer in the pot. Note at what temperature the thermo opens.

Compare the temp at which the thermo opens with the degree stamped on the thermo housing.

After several tests like this, perhaps the thermo is functioning as it should. Maybe you need another thermo that opens at a lower temperature.

If in doubt, install a new thermo. A malfunctioning thermo could cause you to lose your engine by overheating and seizing up.

O J

trapper · Post by **trapper** » Sep 5th, '11, 22:21

replaced thermostat first and engine worked ok for a time then had to replace impeller---I guess you may consider looking at both.

sgbernd · Post by **sgbernd** » Sep 5th, '11, 23:51

I assume you have the MD7 engine, raw water cooled. I assume you you tested the thermostat as described and find it good (it should start opening around 62C and be fully open at 72C) and that the water pump is working properly.

In the short term, to finish up the season, you may be able to remove the thermostat, drill out the two small holes in the thermostat to much larger holes (like 2mm). This will allow steam to escape more easily and give the engine a bit more head room. But is is only a short term fix.

In the long run, you will need to find the problem(s).

A fair amount has been written about overheating MD7s on these pages, some by myself, some by others. I recommend you take few moments and search the archives as a lot of us have gone down this path, some with more happy results than others.

GeorgeH · Post by **GeorgeH** » Sep 6th, '11, 06:37

Thanks everyone for the suggestions, since I put in a new thermostat and impeller this past winter I was wondering what else could cause the engine to run in the red temp. A sticky thermostat might be the problem (I hadn't started the engine in a couple of weeks so it could be gunk and crud), also I am going to check to see if I can by a thermostat with a lower opening temp since this new one seemed to open closer to the red zone then the previous.

I did put a new impeller in over the winter (and new speed seal gasket and cover) so I don't think its that. I suspect the thermostat, based on most of the board comments, though I put i new one this winter in as well. Thought I was thinking I might try to run it without the thermostat and see if that's the real problem. Any problems with that?

Thanks for the advice, its great to have an active board where everyone's is helpful.
Regards,
George

Klem · Post by **Klem** » Sep 6th, '11, 11:01

While I was doing some work this spring, I put a new thermostat in mine figuring what the heck. After struggling with overheating early this season I pulled it out and discovered that the new one opened about 20F high. Even if you have a brand new thermostat, it isn't necessarily right.

The most obvious thing to check for is the amount of water flow. If that is good, check the thermostat and make sure that the cooling passages that you can see are not too plugged.

Good luck.

Matt Cawthorne · Post by **Matt Cawthorne** » Sep 6th, '11, 19:03

I did not go through all of the other posts on the board to know if this has been discussed, but raw water cooled engines occasionally need to be cleaned out. My brother had this done to his Volvo engine and it fixed the overheating problems. I don't know if this is a salt water only issue. I believe that the work requires a partial disassembly of the engine.

I had a problem with my Perkins running cold for a number of years. I replaced thermostats etc only to find out that the temperature sensor was the problem. The cooling system was working correctly.

johnny of STORK · Post by **johnny of STORK** » Sep 6th, '11, 20:48

I had this problem a couple of years ago, and wound up taking the exhaust manifold off, and cleaning out the galleys and holes that come from the engine through it into the exhaust elbow. It took while, but wasn't difficult. There are several holes something like 1.5 inch across that seem to fill up with crud near the gasket surface, so they are pretty easy to clean out with a piece of wire. There are also a couple of small ones, maybe 1/4 inch across, and they are a little harder, but doable. I also reamed around as far back into the head as I could reach with a wire, and I think most of the corrosion was in the manifold, and near the gasket. This gives you a good opportunity to take out and completely clean the thermostat and it's seat, and boil the thermostat in water to check it, as mentioned above. Mine had quite a bit of corrosion on it, suggesting that it may have been restricted in its movement, as well. Now when I haul STORK, I run the motor for a few minutes circulating a fresh water rinse with some vinegar in it. If I have the problem again, I'll post about it, and how long the cleanout lasted.

Johnny

Jeff and Sarah · Post by **Jeff and Sarah** » Sep 6th, '11, 22:45

Funny that you mention your issue when you did. My wife and I left the dock Sunday and about 3 minutes out we heard the temp alarm. The engine had been running fine at the dock for about 30 minutes before we shoved off. My engine is a Volvo 2003 (model #, not year). I brought it back down to idle and a few seconds later the alarm extinguished. We headed back to the dock at about 1/2 power and the alarm never came back. We were happy the alarm came on when it did because we were just about to go through a narrow draw-bridge that would have been impossible to sail back through if needed.

This weekend's weather was too nice to spend time tinkering with the engine so I left it and headed to the marina pool. I'm pretty convinced it was just a stuck thermostat so I plan to throw in a new one next time I'm at the boat. There is always a chance I had just sucked some debris against my raw water intake, but a new thermostat never hurt.

Jeff

GeorgeH · Post by **GeorgeH** » Sep 8th, '11, 13:13

Wanted everyone who is following this string to know that I went to Steve's Marine Services in Patchogue, NY who is a Volvo diesel repair facility and he suspects that the overheating is caused by too little water getting through the exhaust elbow. He said the reason the engine goes from the red zone back down to green is probably steam pressue pushing enough water through the elbow to cool down.

He said I should replace exhaust elbow, about $400 dollars from Volvo. He said I could probably continue to run the engine at low rpm's in and out of the harbor, so I can sail through the month before hauling her out.

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