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Old 23-08-2010, 10:18   #1
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Repairing Head Gasket on Yanmar Engine

I THINK Ihave a failed head gasket on my Yanmar 3GM30 diesel @ 900 hrs. It is running hot and I have replaced all the water lines, cleaned the exhaust manifold , REPLACED the exhaust elbow (expensive & did not solve overheating problem , checked the inlets are not blocked, checked the water pump">raw water pump & impeller, which SEEM OK. I am going to use a temp gun to see if there is a particular cylinder overheating.

My final though is that it is a blown head gasket.
My Q = what should I start to remove \ unbolt to save some bucks before getting the mechanic in. Is there any other way of checking if it is the head gasket? Is there any net source or post on this forum on exactly how to go about this. I have Nigel Calder's big book and diesel engine book but haven't looked there as yet as I am in Greenland searching for Texas T and the boat is in OZ (Cairns)

I am heading abck in a 3 days so any advice would be appreciated.
PS I usually do all the maintenance on my engines and have the Yanmar workshop manual.
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Old 23-08-2010, 10:24   #2
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have you pressure tested the cooling system yet?
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Old 23-08-2010, 10:28   #3
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Are you sure it's running hot? have you confirmed the engine temp with a gauge other than the engine gauge or alarm?
Have you lost any coolant lately?
When you say "cleaned exahaust manifold" Can I assume that means you ran a brush through all the heat exchanger tubes?
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Old 23-08-2010, 10:37   #4
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What never monday and SaltyMonkey say, and:

Unless you have water somewhere you shouldn't it is not likely a head gasket. Do you have an unusual amount of smoke? Is the engine running rough? Losing coolant? Water in your crankcase?

An overheating problem by itself is not likely a head gasket problem.

Have you ever lost raw water impeller blades and never found them?

Are you positive that you don't have a restriction somewhere in the cooling system? How about the exhaust system? Any collapsed or soft hoses anywhere in the system?

You could try feeding cooling water into the engine from a bucket that is being filled with a hose just to make sure that the inlet isn't plugged up.
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Old 23-08-2010, 11:38   #5
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Have you ckd the thermostat,not familar with yanmar but assuee they have one.marc
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Old 23-08-2010, 12:33   #6
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Have you ckd the thermostat,not familar with yanmar but assuee they have one.marc
Wow, can't believe I missed that one. I guess I "ass-umed" that had been done.
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Old 23-08-2010, 12:55   #7
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Thanks Guys
I did check the thermostat. I even swapped over from the other engine. That's one of the few good things about having 2 engines. You can swap & compare.

I already had another temperature sensor attached (?Dog watch) The engine was running fine at same temp as other one but over last few months has been getting hotter.

White smoke.
Oil looks Ok
This engine is only raw water cooled so does not have a fresh water radiator. So no water reservoir to check for water loss or pressure test.

Raw water pump impeller is intact. Not sure if PO lost impeller blades.

How do I tell if water pump bearings have gone? Pump impeller seemed to turn OK. The water pump is 8 yrs old. Should I dismantle water pump to check bearings. I only checked the impeller.

No collapsed or soft exhaust hoses. Water outlet seems to be pumping same amount as usual.

NO I haven't run a brush thru the tubes because I don't think that applies as it is not fresh water cooled. I took the exhaust manifold outer cover off and cleaned a little crud out of there.

Thanks for the input
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Old 23-08-2010, 14:21   #8
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Okay, white smoke could be water in the exhaust or unburnt fuel.

Raw water pump plates may be grooved so the impeller is not as efficient as it should be. Some plates can be reversed. Check both plates.
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Old 23-08-2010, 14:46   #9
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Quote:
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NO I haven't run a brush thru the tubes because I don't think that applies as it is not fresh water cooled. I took the exhaust manifold outer cover off and cleaned a little crud out of there.

Thanks for the input

True, no heat exchanger tubes on an engine without fresh coolant. I had an A-4 that was also heating up, I just filled the engine with radiator flush to remove all the insulating salt deposits, flushed several times with a hose, and all was well (after clearing several loose crud blockages at the mixer).
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Old 23-08-2010, 14:49   #10
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Sea chest? marc
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Old 23-08-2010, 15:30   #11
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Had same problem turned out to be sea weed got into the front of the heat exchanger, cleaned it out all okay now, have 1000 hours on engine
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Old 23-08-2010, 16:54   #12
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How do I tell if water pump bearings have gone? Pump impeller seemed to turn OK. The water pump is 8 yrs old. Should I dismantle water pump to check bearings. I only checked the impeller.
Look at the pump, is it corroded anywhere around the openings in the middle? This would indicate a seal failure. My experience is the bearings will last until they get sprayed with salt water due to the lip seal failed. There is normally a slinger (rubber O ring) that is visible between the lip seal and bearings that will save them if the leak is caught early.
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