Engine Overheating

Reprinted from Healeys West, the official publication of the Austin-Healey Club of Australia

Originally printed in the Austin-Healey Magazine, June 1996


Recently I experienced continual overheating and loss of engine coolant with the engine in my 100-6. After trying all the usual remedial measures, I stumbled upon the real reason.


The lip that holds the radiator cap in place on the filler spout had worn away. The effect this had on the cooling of the engine was to reduce the spring tension on the radiator sealing rubber and therefore reduce the radiator cap pressure.

When the engine reached operating temperature, normally the 7 lb. Cap pressure would be sufficient to maintain the seal at the filler neck: With the lip of the filler neck being worn away, this effectively reduced the spring tension and therefore the sealing pressure of the radiator cap.


What this means, is that, as the engine builds up to its operating temperature, it also builds up pressure in the radiator. With the reduced “cap pressure” caused by the ill fitting cap, the pressure being generated as the engine was getting hotter would cause the cap seal to lift at the lower that normal engine temperature and send all the coolant out of the overflow pipe.

A remedy has been achieved by soldering a new filler-radiator cap housing into the radiator header tank.


I trust this bit of advice will save other enthusiasts the trauma of expensive recording, head gasket changes, etc., for the sake of a radiator cap filler housing.


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