Yanmar 2gm overheat alarm

[jmce1587]

My engine thermostat Alarm light/alarm buzzer sounded today shortly after departing slip. The engine had been running fine at the slip for about 20 mins before departure. I immediately shut it off and began diagnostics. I checked the raw water intake and it was clear. Also water is pumping from stern exhaust. Removed the water pump and checked the impeller. It was in good condition. Belt is also good. I then removed the thermostat. Ran the engine and no alarm. Went sailing for a few hours. When entering the channel to return home, started the engine and after a few minutes the alarm came on again much to my surprise. I shut down the engine and sallied into my slip. I'm not sure from here what else to check. Could the relay be bad? Sending unit?

Any suggestions/ thoughts are appreciated.

Thanks, Jerry

 

[Terry Lockhart]

Start by confirming the engine temperature.
Use a digital laser temp gun.

 

[Alan Gomes]

I agree with confirming the engine temperature using a digital laser thermometer. You can get one really cheap from Harbor Freight.

As for the temperature sensor, that is simply a temperature sensitive switch that provides a pathway to ground and completes the circuit that sets off your buzzer. Check the wiring to make sure that the wire going to the switch is not somehow coming in contact with ground in some other way.

Next, checking the switch itself is simple. Remove it from the engine and heat up a pan of water at or above the temperature at which the sensor should close. I believe your engine is raw water cooled, just as my 1GM is. If so, the temperature switch closes between 148-154 deg. F. If your engine is fresh water cooled then the closed temperature is 193-202F. Attach an ohm meter to both the probe part of the switch and to the place where you removed the wire when you took it off the engine. You can tell from the ohm meter whether the switch is open or closed. Actually, you should be able to hear an audible "click" when the switch closes even without the meter. But check it with the meter regardless. Then, remove it from the hot water. As the switch cools the switch should open back up. Really not much to it.

Good luck and let us know what you find out.

 

[Alan Gomes]

Here's the test procedure from the Yanmar manual

See attached file.

 

[kloudie1]

Add to above: Coolant level in the heat exchanger OK? (don't open when the engine is hot!) Alternator belt OK? (it drives the coolant pump to circulate coolant through the engine and to the heat exchanger) Exhaust elbow clean?
The thermostat circuit on that engine is not like a car's .. It has to open one hole (block circulation) and close another (block bypass) to function. Don't run the GMF series engines without a thermostat. You can test the thermostat by heating it in a pan of water .. It should start to open at about 160F and be fully open at 185F
If none of that, then time to pull the heat exchanger and make sure all the tubes are clean and open.

 

[Warren Milberg]

Good advice above about checking thermostat and sender switch. I also suggest checking to see if you have any abnormal growth or other obstruction (i.e., plastic bag,etc) wrapped around your shaft and/or prop. That would cause an overheat alarm in some cases.

 

[Bill Roosa]

For future reference if there is sufficient water coming out the tailpipe then your raw water circuit is OK. Look for problems elsewhere
I'd check the thermostat before I went to replacing parts. take it out, put it in a pan of water and heat with oven thermometer in the water. Should open dramatically at the temp stamped on it.
The engine coolant pump (anti) is pretty bulletproof if it is spinning. the temp sensor and the temp idiot light/buzzer are two different items so if they both go bad at the same time I'm thinking that is pretty bad luck. The engine temp gauge did indicate an overheat condition is my assumption and "panic" ensued after you looked at the idiot light, heard the buzzer AND looked at the temp gauge.
Not at all sure Warren is understanding how a diesel works. If the engine is operating at MAX POWER there should still be sufficient reserve cooling capacity to keep it cooled. Would be pouring out blue smoke but would not overheat just do to being overloaded. Also AbiNormal growths would be noted as a vibration....... Really not thinking this is the problem.

 

[jmce1587]

Thanks for all the good info. Turns out I sucked in a finger mullet in the sea water intake enough to impede water flow and overheat the engine. This gave me a good opportunity to thoroughly inspect my cooling system and make necessary repairs.

 

[kloudie1]

Laughing, Jerry.. I helped a friend with overheating last year .. Yes, we found a fish, kinda mushed up in the thermostat.. He now has a raw water strainer.

 

[Claude L.-Auger]

Laughing, Jerry.. I helped a friend with overheating last year .. Yes, we found a fish, kinda mushed up in the thermostat.. He now has a raw water strainer.

Laughing too as it could have been worse. I always had a raw water strainer, but after picking and having to go under to remove a used condom :cussing:, I now also have a through hull intake strainer, not only on the engine but also on the wash-down pump through-hull.

 

[jmce1587]

Laughing too as it could have been worse. I always had a raw water strainer, but after picking and having to go under to remove a used condom :cussing:, I now also have a through hull intake strainer, not only on the engine but also on the wash-down pump through-hull.

This will definitely be on my to do list on next haul out. Will also add one for ac intake

Thanks again guys for the good info

 

[Warren Milberg]

For Bill Roosa:
1. I didn't note any comment by the original poster about running his engine at max rpm when the overheat alarm occurred.
2. I have two friends who have had Yanmar overheats directly related to fouled props and shafts, and perhaps most importantly,
3. I don't claim to be an engine expert, but Nigel Calder does. Take a look at pages 71-72 of his "Marine Diesel Engines" to get a better understanding of why I posted the possibility of fouling being a (one of many) potential cause(s) of the overheat alarm.

 

[eliems]

If your problem is anything like mine, you will have the alarm go off again at some random time ... let us know when it does.

 

[Bill Roosa]

Hey Warren.
My point is if it is designed to run a max power and not overheat then it should not overheat at a lower power level.
A fouled prop alone will not cause an engine overheat. I suspect the heat exchanger is also fouled and not up to its job or there is something obstructing the raw water flow. you did say directly related to" so I'm thinking that does not mean "exclusively due to"
And I have been working on diesels for the last 25 years so ......
Love you man

 

[Benny17441]

Just one more possibility. The wiring harness. On older boats the harness sometimes chafe in those tight bends around sharp fiberglass edges. It usually starts with random shorts which may lead to temporary starting problems or false buzzer alarms. A visual inspection of the harness will usually reveal those spots where the cover and wire insulation may have been compromised.