lost a bit of water the other day, onto the exhaust manifold causing a bit of steam. I have pressurized the system to see if the expansion tank was cracked or any other sort of leak was involved. It held high pressure for a long time so was assured it wasn't the tank to blame.
Tonight I have changed the thermostat as I took the bleed screw out of the top hose and it was empty. I removed the housing and changed the stat and put it all back together.
I took both bleed screws out, and filled with coolant, kept filling until there were no air bubbles visible at the bleed screws. I then topped up the expansion tank to max and let the car idle up to temp.
There were no leaks so I assumed the job went okay. Water was then rising out of the expansion tank. I drained a bit off then a few minutes late, it rose again. Checked the top hose bleed screw and it seemed empty again????
Is this the head gasket failing and pressurising the water system or could it be the water pump not circulating the water?? Both seem plausible to me :/
Any help is greatly appreciated before I pay for expensive tests/checks.