MY EXPANSION TANK IS NOT HOLDING THE CORRECT
Are you using any water as far as driving does the temp gauge go up higher than usual,, as the last one i done was a loose head bolt and wasent tightened up in correct way and 1 was only tightened up twice and they missed 4 left from the rear and allowed the gasket to bypass compression gasses into the coolant system ,which done the same as yours ???.
but pumping up pressure in cooling system is about 20lbs max and the engine compression is more than 110lbs thats why,.,.,.,
Let me know how you go . RON
1997 Jaguar XK8
on Oct 15, 2011