Overheating yanmar 1gm10 after short run.

[Tammany]

Having overheat problems with my 1GM10.
Start engine from cold, water flow seems good and being ejected from the exhaust. After 5-10mins or so starts beeping with overheat alarm but at the same time their seems to be very little water coming out the back, certainly a lot less than from cold.
Attaching hose to water pump exit and water flow seems good, whatever is going on it happens as it gets hot so I assuming when the thermostat changes position.

Is this indicating a faulty thermostat or calcified/blocked cylinder head?

 

[GrahamP]

I had a similar problem. Found a blockage in the T section that goes into the engine block. Cleared it with a small screwdriver.
Check this video :-

The T section is described at 5:25 into the video
That's one possibilility and is easy to check!
Graham

 

[Tammany]

I had a similar problem. Found a blockage in the T section that goes into the engine block. Cleared it with a small screwdriver.
Check this video :-

The T section is described at 5:25 into the video
That's one possibilility and is easy to check!
Graham

Going to investigate further and remove all the coolant hoses and give a good clean. Will take some wire with my to have a good poke around the passages as much as I can before resorting to removing the head. If I manage to clear it will run an acid flush afterwards.

 

[cherod]

Had the same problem , alas it was the head , new head sorted the problem , not too difficult a job ( depending on ones ability and engine location ) the head is the red bit

 

[Tammany]

A new head would be nice but apart from cooling then it starts and runs perfectly. Engine including head was rebuilt 5 years ago and it hasn't had that many hours on it. Blocked cooling passages doesn't need a new head, it might have to come off for a proper descale but it definitely won't need replacing.

 

[cherod]

A new head would be nice but apart from cooling then it starts and runs perfectly. Engine including head was rebuilt 5 years ago and it hasn't had that many hours on it. Blocked cooling passages doesn't need a new head, it might have to come off for a proper descale but it definitely won't need replacing.

Thing is tammy , you wont know until you strip down , they have a problen between the inlet port and the exhaust ( from what i remember ) it erodes , are you blowing steam or blue smoke . Mine had been “ repaired “ previously , i think welded , but it is not permanent , new head is not terribly expensive in fact not much more than i was quoted for a good second hand one , fairly common fault i have been told .. hope you find simple water issue ,

 

[Tammany]

They erode between the exhaust elbow and exhaust valve. I had that when first purchasing the engine which is why I re-built it. I then fitted an aftermarket stainless elbow which is far better than the crap yanmar ones. That gives different symptons to this, poor running and starting due to lack of compression when the exhaust valve is closed mainly. A new head is approx £1200 including extra fittings/gaskets etc so not a cheap repair.

 

[andsarkit]

I have had a partial blockage in the hose coming out of the top of the pump. It will not take long to check this pipe and the thermostat for any deposits