wolfweb

He's found it was the new radiator cap. It was an aftermarket one, not subaru genuine part. The are two metal lugs that hold it on tight. One of these lugs was smaller than the other. This meant under pressure one side of the cap popped off. It wasnt off enough to notice, just enough to lose pressure which resulted in the overheating. A new cap was fitted and no overheating, no loss of fluid so far. He seems to think the loss of fluid was it being forced out of the radiator into the reserve tank. I again asked him why it had never overheated using the original cap which he said failed a pressure test and he said it probably held enough pressure? But it was losing fluid with the original cap, so something seems to have been wrong with it, again he says it was probably forced into the reserve. Still monitoring the fluid to make sure there is no more loss. Thanks for your help everyone, amazing how you all got it so right not seeing the car and relying on my noob relaying of the facts. I fot it wrong about the pressure test. The radiator never failed that. The original cap failed the test. He did not test the new cap which i guess is normal but that would have saved him lots of trouble and my subie overheating.. I hope there is no damage, he said no because it passed the block test and there is little else that could be wrong due to the overheating, according to him.

here's what happened: I took it in for a service, the mechanic said the radiator failed a pressure test so he ordered a new cap. Couple of days later I had the cap fitted, the radiator passed the pressure test. The next day after a 30 min trip the car boiled, temp into red just after I stopped at my gate. I've never had trouble with overheating beofre he replaced the cap. Took it back worried it was a head gasket or cracked head. They did a block test on it, it passed. he found a small leak in a hose but doesnt think that caused the overheating. Now he's checking the thermostat and said he'll take it for a drive today to see how it performs.

My mechanic replaced the radiator cap on my subaru forester 2003 xs saying the radiator failed a pressure test and seemed to be losing coolant somewhere. Another pressure test after the new cap was fitted succeeded. Next day after a 30 min drive, soon after stopping at my gate, the temp went into red, radiator has boiled, steam coming out of cap and fluid sprayed over engine. I immediately turned off the engine. I never had trouble with overheating before the new radiator cap. What could have caused that? Could the overheating have now damaged the engine?