Overheating Yanmar

My Yanmar 4JH2-DTE overheated on sunday and coolant came out of the expansion tank.
The engine is 7 years old but i have only had the boat 2 years and it had 150 hrs on it when i got it and now has 310 hrs.
I have never changed the coolent since i got it.
I was planing to drain and flush the system with Radflush and then refill with new coolant. Also i`ll check to make sure the thermostat is working.
The raw water side seems to be pumping ok but i`ll check the impellor.
If this fails to cure the proplem then i was thinking of taking apart the heat exchanger to see if its blocked up with crud at all.
The coolant in there seems to be a brown colour.
Any ideas where else i should be looking or what it might be ?
I just hope it`s not the head gasket!!!!


Alan

Re: Overheating Yanmar

The raw water side seems to be pumping ok but i`ll check the impellor.

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How did you check it?
I would change the raw water pump impeller and try it again. Those impellers should be replaced every couple of years. If they don't pump enough water to cool the heat exchanger, it will force coolant out of the expansion tank.

Re: Overheating Yanmar

Don S said:

How did you check it?

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I haven`t had a look at the impellor yet but I changed it last year and water seems to be going into the strainer and out the exhaust ok.
I can`t get to the boat and make a start untill next Wednesday.

Alan