Overheating

[8916]

Many thanks to all who replied to my engine heating problem. Someone asked for more information, so here it is,
Merc. 4cylinder engine with integral water pump which is expected to circulate the fresh water round the keel cooling system. This is a lot more work than with a heat exchanger. I have read that these pumps are not up to the job! There is a header tank which has one pipe only comming out, there is no filler cap ie. 7lb. rad cap.
The keel cooler is outside the hull. Sea water is only used for exhaust cooling were it leaves the manifold,so the engine relies on fresh water cooling entirely. My feeling is thet the header tank needs an inlet and outlet pipe and a pressure cap fitted which I intend to do asap I have a problem trying to understand the thinking behind the original design. The water is getting round the circuit but not quickly enough . Each engine is independant of the other. Colin

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[BarryH]

The header tank is there to allow for expansion and contraction of the cooling water. So I can't see that adding extra pipes will aid the situation, propbably make it worse. There must be a fill point for the cooling system. Normally the header/expansion tank which is normally the highest point in the circuit.

If theres only one pipe from the header then it looks as if its not self bleeding. Is there any airlocks in the system.
Are the cooling tubes free from growth. Is there any restrictions in the tubes. I'd be careful about adding pressure release caps to the system. It my be running at higher pressures than the 7 odd lbs that you think. Most systems with expansion tankes run at higher pressures.
The pumps run at the engine speed. So if they're pumpimg at 1000 rpm they'll still be pumping at 2500 rpm. The flow rate is being slowed somewhere. Maybe the keel cooling tubes are able to handle the heat transfer at lower revs but are ineeficient at higher rpm due to some restriction/growth/ damage. What are the cooling tubes made of. If steely boat they're probably steel to get around mixing metals in the water etc. Is there any access points for inspection on the tubes. Rodding points etc.

Just a few points that you may have already looked over, dunno, you hadit out the water to have a look?

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