What else could it be?

Hi

Last year my car needed a new head gasket. Recently I developed some serious coolant leaks and since it took me a while to deal with them I believe my HG blew again. I say this because the cooling circuit is building up a lot of pressure. The hoses become stiff 5 or 10 minutes after starting the car. I took the car to a mechanic and despite what I just mentioned he wasn't too convinced the problem came from the gasket even though he couldn't explain where the pressure is coming from. Still convinced it's a blown HG I ran a chemical test and to my surprise it came out negative. I tried 3 times and the result was the same (the coolant did overflow suddenly though). The car doesn't overheat, the thermo is working well and as far as I can tell there is no oil in the coolant.

I don't know what else to do. Any thoughts?

When mine started playing up... turned out to be the Heater Valve playing up. Building up pressure and my radiator fan was kicking in all the time. Was ok on short runs then on longer runs the pressure and temperature would rise.
Changed the HV and the problem was rectified...might be worth ago.

My first gues would be a sticking thermostat, or non functional water pump...

Cartman said:

My first gues would be a sticking thermostat, or non functional water pump...

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Wouldn't a knackered water pump make the car overheat though?

it would, but a symptome of oveerheating is pressuer building in the coolant