Engine Overheating

[Bill Dorsey]

I have had an of and on problem with my Yanmar 2GM20F overheating. It first happened while in a long line of boats waiting for a bridge to open. The overheating buzzer came on. After a cooldown I saw that the fresh water was low and a lot of water was in the resevour. I put the water from the resevour back in the engine heat exchanger and proceeded without any further problems. Since then I have cleaned the heat exchanger, replaced the fresh water cap, and checked the resevour system for leaks. None of these have worked. I still get overheating when I idle for a long time, and I always have to return the fresh water from the resevour to the heat exchanger after each day of motoring. Just recently, I had this problem occur near the end of a long day of motoring into a heavy sea and wind. Again the resevour was full and after returning the water to the heat exchanger, I proceed with out further trouble. Any thoughts on this problem would be appreciated.

 

[Mark M Smith]

you have a leak

in your freshwater system.

 

[Steve Dion]

Low water.

Bill:It seems strange that this would happen when idling. What I would suggest is that you start at your raw water intake seacock. Remove the intake hose and be sure that you have a good water flow. Then check your strainer. Check all of your hoses while you are idling (be sure that they are not collapsing). Once you have checked out the raw water side of the system (do not forget to check the mixing elbow too), start on the fresh water side. About the only place that water can go is to a leaking head gasket or thru the heat exchanger. If it was the head gasket you would probably see steam in your exhaust.You may also want to consider removing your heat exchanger and having it pressure tested. Water from the raw water side and the fresh water side both pass thru this exchanger. If you have a leak internally you can be loosing coolant from the fresh water side to the raw water side (which would just go out the exhaust).

 

[Sam Morris]

Agree with Steve!

Check your SW System. It may be the cause of the overheated FW. Feel the water into and out of the SW strainer upstream of the SW Pump. It should be as cool as the SW. If its too hot to touch, the problem is probably in the SW System. If not, the problem is in the FW cooling loop.

 

[Ken Osborne]

Hot water

All the responses to your question are good ones. You don't say how old your engine is, but I have a 1995 29.5 with a 2GM20F. I changed the thermostat and at Yanmar's recomendation, Changed the green Anti-freeze to the new Red colored anti-freeze which is supposed to be much better. If your thermostat is not opening completely ,the engine will tend to over heat at idol because of low engine rpms and a restricted flow because of the half open thermostat. If this were my engine I would change the thermostat and anti freeze first. Good luck.