Mystery coolant leak on 1.0 Ford Focus
Hi, I am following up on my question already asked here https://www.honestjohn.co.uk/AskHj/UserQuestion?questionId=225700&verify=ZTyRXe5pGLMzCtxkX%2FbTZJ2pRFVI9HRBQ3uW0ntkMsk%3D
Till now I have taken the car to three garages and all were unable to spot any leak during the pressure test. One guessed might be head gasket, one guessed it might heater matrix, no one was really sure as they didn't spot any leak. I am so very confused now as another observation I had was I think it leaks when I start the car as I see a small puddle on my driveaway but that too looks like it doesn't happen always. Can you please advise what component can cause intermittent leak as it seems like it and not always after every drive or starting the car.
Till now I have taken the car to three garages and all were unable to spot any leak during the pressure test. One guessed might be head gasket, one guessed it might heater matrix, no one was really sure as they didn't spot any leak. I am so very confused now as another observation I had was I think it leaks when I start the car as I see a small puddle on my driveaway but that too looks like it doesn't happen always. Can you please advise what component can cause intermittent leak as it seems like it and not always after every drive or starting the car.
Asked on 18 March 2026 by Santosh Gawde
Answered by
David Ross
It is possible that the leak is occurring on your driveway and not when the vehicle is tested at a garage because it is due to failing seal when the engine is cold. In this instance it is possible that as the engine warms the seal expands and prevents the leak, which may explain why it does not occur when tested. This could be a seal in the heater matrix or the coolant hoses - if it were the head gasket then we would expect to see other symptoms such as sludge in the expansion tank and white smoke from the exhaust. One option would be to use a UV dye in the coolant which would help trace the source.
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