Yanmar overheating

[admorton]

I have a Hunter 28.5 with a Yanmar 2GM20F engine. The engine overheat light comes on after about 10 minutes on fast idle. I have tried everything I can think of to fix it. I have replaced impeller and cleared the line of parts of the previous broken impeller. I've replaced the thermostat. I have looked at the heat exchanger and it looks ok, one tube is blocked, but all others are clear. I did all of this earlier this summer and I swear that that the light didn't come on again until just this week. I suppose the light has been on all along (dim bulb and bright sunshine) but I don't think so. I know sea water is going through heat exchanger because I noticed a small leak in the hose that goes to the exhaust. Hose that comes out of the heat exchanger is cool, not hot, this is a bad sign? All fresh water hoses are hot. Could it be a bad water pump? How can I tell? Shaft is not loose and its not leaking. Could it be a bad temp sending unit? I'm at my witts end and need help from somebody smarter than me.

 

[JamesG161]

It could be many reasons. To do more trouble shooting here is a valuable tool.
http://www.harborfreight.com/infrared-thermometer-93984.html

If your exhaust is above water line then there should be water "spitting and gurgling" out that port.

One last thought...

When you replaced the impeller, did you use the gasket provided with the impeller? If you use a "thick" gasket, the the pump with bypass.
Jim...

 

[JamesG161]

I hate type spell checks...

the the pump WILL bypass.
Jim...

 

[Charles Erwin]

There are two pumps involved - sea water and circulation. You have eliminated the impeller debris left over from a prior sea water pump impeller failure. The sea water that leaves the heater exchanger (and goes overboard) is cool. You reckon there is good flow because there is a leak at the discharge hose that runs from the heat exchanger to the mixing elbow.

First - sea water flow should produce no or insignificant pressure anyplace in the system. A leak - even small one - in the discharge hose is a symptom of an obstruction in the mixing elbow - that is down stream from where seawater discharge enters the mixing elbow. The mixing elbow should be examined to rule out any obstruction.

Next - the sea water is cool because the discharge hose is cool. This symptom suggests motor coolant - the antifreeze side - is not circulating well. The first suspect is a thermostat that has failed in the closed position but you have ruled this out. The next suspect is the circulation pump failing to move coolant because if it cannot there will be no movement of coolant through the heat exchanger and so very little effective cooling. Obviously there are other things that can block motor coolant flow in the antifreeze circuit - a space heater, a water heater and so forth.

I would start by verifying that the anti freeze coolant flows well. Probably you should not rely on the temperature of the discharge hose all that much. An obstruction in the seawater discharge is still a possibility.

Charles

Edit: ps To verify coolant flow remove the heat exchanger cap. Make the motor hot. Eyeball down the cap neck with flashlight/mirror if necessary. You will see flow if the thermostat is open and there are no other obstructions. All of this assumes that you have plenty of coolant - no leak.

CE

 

[BigEasy]

Had the same problem on my previous boat, a 1988 Hunter 33.5, with a 2GM20F Yanmar. Did the shotgun approach and flushed the cooling system. Replaced the raw water impeller. Removed the heat exchanger and cleaned it with a rifle cleaning brush--it was full of marine growth and sand. Changed the thermostat. Removed and power washed the interior of the mixing elbow--there was quite a bit of carbon buildup. Should have replaced it as it is a recommended maintenance item. Problem fixed, no more heating at higher engine RPMs. The boat was about 10 years old when I purchased it; I am sure that many of the above items were never done previously.

 

[Benny17441]

What is happening with the alarm buzzer? If the buzzer is not going off when the light is coming on there is either a bad buzzer or a problem in the wiring. This would be the first issue I would correct. From your description it seems that your engine could be running a little over temperature but it does not seem there is definite evidence of any overheating. There is no reason to directly associate this occurrence with what happened two or three months ago so start diagnosing as if it is a new problem. I would then start by checking the sea water intake port to make sure I have not picked up a plastic bag or sea grasses. After that I will move to the hoses and the pump, check the impeller once more and once you are satisfied the raw water system is working well then move to the closed cooling system on the engine.

 

[admorton]

Charles, I was leaning toward suspecting low flow in antifreeze system. Are you suggesting that I run the engine with the heat exchanger cap off to verify flow? I'm not following you. How can I see coolent flow?

 

[admorton]

What is happening with the alarm buzzer? If the buzzer is not going off when the light is coming on there is either a bad buzzer or a problem in the wiring. This would be the first issue I would correct. From your description it seems that your engine could be running a little over temperature but it does not seem there is definite evidence of any overheating. There is no reason to directly associate this occurrence with what happened two or three months ago so start diagnosing as if it is a new problem. I would then start by checking the sea water intake port to make sure I have not picked up a plastic bag or sea grasses. After that I will move to the hoses and the pump, check the impeller once more and once you are satisfied the raw water system is working well then move to the closed cooling system on the engine.

First time it happened this week the buzzer did come on. After then the light came on as I ran various test but buzzer didn't always come on. I checked sea water strainer and intake seems to be clear.

 

[Charles Erwin]

Pardon my inclarity. Unscrew cap and set side. Motor running. When motor temperature is hot look down the cap neck into the exchanger chamber and see if you have coolant flowing - you know - current flowing through your field of view (one end to the other of the exchanger) at a rate more like the Rouge River less like the MIssissippi River. Clear?

Charles

 

[admorton]

There are two pumps involved - sea water and circulation. You have eliminated the impeller debris left over from a prior sea water pump impeller failure. The sea water that leaves the heater exchanger (and goes overboard) is cool. You reckon there is good flow because there is a leak at the discharge hose that runs from the heat exchanger to the mixing elbow.

First - sea water flow should produce no or insignificant pressure anyplace in the system. A leak - even small one - in the discharge hose is a symptom of an obstruction in the mixing elbow - that is down stream from where seawater discharge enters the mixing elbow. The mixing elbow should be examined to rule out any obstruction.

Next - the sea water is cool because the discharge hose is cool. This symptom suggests motor coolant - the antifreeze side - is not circulating well. The first suspect is a thermostat that has failed in the closed position but you have ruled this out. The next suspect is the circulation pump failing to move coolant because if it cannot there will be no movement of coolant through the heat exchanger and so very little effective cooling. Obviously there are other things that can block motor coolant flow in the antifreeze circuit - a space heater, a water heater and so forth.

I would start by verifying that the anti freeze coolant flows well. Probably you should not rely on the temperature of the discharge hose all that much. An obstruction in the seawater discharge is still a possibility.

Charles

Edit: ps To verify coolant flow remove the heat exchanger cap. Make the motor hot. Eyeball down the cap neck with flashlight/mirror if necessary. You will see flow if the thermostat is open and there are no other obstructions. All of this assumes that you have plenty of coolant - no leak.

CE

Ah, I think I got it. I don't have a cap on the top of heat exchanger or a cap for fresh water system on engine. I have an expansion tank installed in adjacent compartment.

 

[admorton]

I hate type spell checks...

the the pump WILL bypass.
Jim...

I didn't have a new gasket so used the old one.

 

[kloudie1]

all good things to look at.. On the exhaust mixing elbow, the place where the hose from the exchanger comes into the elbow.. make sure that is clear.. pull the hose and run a wire through if you can. you may have some more impeller debris plugging that..
Charles suggestion is good .. take the cap off when the engine is cool then start it and let it warm.. The cap is where the hose from the expansion tank hose meets the top of the heatex housing. If none of that works, check pump belt tension to make sure pump is turning fine.. and last, check the impeller to make sure it turns when the shaft turns..

 

[admorton]

I also have a remote fill (accessible from cockpit ) with a big hose that connects to the heat exchanger. Can I just undo the hose to look in the heat exchanger? Also, when I pulled the guts of the heat exchanger to look for debris I noticed a conspicuous lack of water on the engine cooling side. Didn't seem normal to me.

 

[JamesG161]

Here is another handy tool.
http://yanmar-marine.marineservicemanuals.com/Yanmar-2GM20F-Marine-Diesel-Engine-Service-Manual.html
This $5 manual will give you the same info as a engine service tech uses.

I also have a remote fill (accessible from cockpit ) with a big hose that connects to the heat exchanger. Can I just undo the hose to look in the heat exchanger? Also, when I pulled the guts of the heat exchanger to look for debris I noticed a conspicuous lack of water on the engine cooling side. Didn't seem normal to me.

Wow I hope not. The fill cap for you (antifreeze/fresh water reservoir) is in you Cockpit??!!

Gasket for a lot of pumps must be "thinner than paper" to allow the contact plate (pump cover plate) to seal against the impeller. The fact that you could reuse it, says I am wrong about you pump.

So far...

It looks like an antifreeze/fresh water problem. Lack of fluid level, pump, thermostat, etc.
This fits, since it takes time for engine temp to rise and open the thermostat and then send an alarm.

Jim...

 

[Benny17441]

No buzzer; I think you may have a short in the wiring harness from engine to control panel. The harness extension is routed through the interior hull around sharp fiberglass corners which with many hours of hull flexing it leads to chaffing and shorts. The chaffing usually begins by cutting into the outside cover and then into the insulation of a wire or two causing shorts and erratic behavior affecting usually the buzzer and warning lamps as those comprise the majority of the wires inside the harness. I'm not saying your engine might not be overheating but just pointing out that something is afoul with the alarm and warning circuit and should be corrected to eliminate the possibility of a false alarm due to a short. Breakage on the harness cover usually happens around bends and can be visually spotted, the hard part is crawling under the cockpit sole.

 

[admorton]

Thanks to all of you that commented on my problem. Great comments! I think this one is put to bed. Turns out that the fresh water system (the engine coolant with antifreeze ) needs to be full of liquid. My remote fill hose with the pressure cap had a high spot in the line so I thought it was full but the liquid was not getting to the engine. I shortened the hose so it's a straight gravity feed to the heat exchanger, filled it with water ( took less than a gallon ) and wallah, no more overheating. Ran engine half hour at fast idle with no light or buzzer. By the way, my remote fill is in the lazzertte under the seat in the cockpit. Good idea if done right.

Thanks again to all!

 

[JamesG161]

Great! It always helps when you find a problem. You are now promoted to Senior Captain of your boat. Good thing you believed your alarms.

my remote fill is in the lazzertte under the seat in the cockpit. Good idea if done right.

I had visions of this Radiator cap under the guest's feet. LOL
I still am curious how know the level or even sample your antifreeze? But that is of topic...
Take care...
Jim....

 

[kloudie1]

Strange.?? Sounds like a previous owner put in the remote fill?? and part B: why would he have done that.. I usually don't have to top off but every couple of years.. Have you got a leak in the coolant system? The expansion bottle should keep the coolant full if cap and tubing are all good.. Maybe it was put in to help him with the winterization thing that some folks have to do..

 

[Cmp1110]

My 28.5 also has fill and overflow tank are in the lazzerette also must be factory. I have coolant in the tank but how full should the hose be?

 

[kloudie1]

Interesting.. I am obviously not very familiar with that boat/engine install.. Sorry for the off key info.
Can ya post a picture of the install? Should not need refills regularly..