engine heat alarm

[killick]

If I run my Westerbeke 12 hp diesel engine at high revolutions the overheating alarm comes on after a while and stays on even if I return to lower refs. The temprature guage does not exceeds 80 degrees celcius and if I open the water tank on the engine the water does not boil. I have cleaned the heat exchanger and there does not seem to be an obstruction in the cooling system. The only different thing I have noticed is that there seems to be a vacuum when the engine cools and the rubber pipes are pulling in on themselves. Any advice will be greatly appreciated.

 

[superheat6k]

I would suspect a blockage in the pipe between the header tank and the engine, this would explain why the header tank is not boiling, plus the partial vacuum when the engine cools down. The vacuum is likely caused by contraction as the water cools. Could be the engine is simply air locked - is there a venting procedure for your engine ?

Ignoring the temp gauge, measure the temp at the sensor with an infrared thermometer when it alarms, but first try unscrewing the sensor and see if any air comes out, either engine off or at idle, or from any other vents provided.

 

[VicS]

As above . A pressure cap should allow air to enter when the system cools.

The conventional cap has a secondary valve shown in the picture below being held open with a small screwdriver.
Your cap may be defective or it may be the wrong cap.
Design of caps varies. My Volvo one is totally different.

The reason you are getting an overheating alarm when the engine temperature is only 80C could be due to a faulty sensor for the warning light/horn

 

[killick]

Thank you very much for all your inputs.I am sure I will get it right now.