ive just rebuilt car new hgasket head was tested 2 months ago only put new h gasket on as i have had engine to bits for shells
anyway it runs no probs has no thermostat dont boil while running can take cap off and no water overflow but soon as i turn key off it just wants to explode it preasures up loads WHY any ideas what is causing it

 

If you are running with the cap off, then it is not pressurising the cooling system, which it needs to do to raise the boiling point of the coolant, some bubbling in the tank after running is normal, even when there are no problems, but the cap must be on at all times.
tabetha

 

Aren't you meant to run it up with no cap on to get rid of air locks and such though tabetha or have i got it wrong??

Id check the rad and heater matrix mate i dont think its anything serious or it would do it when running

 

I never run with cap off, not when it is anything over warm, the suction created in the expansion tank when cooling helps to draw air out.
Obviously the capneeds to be on for suction to be created upon cooling, other people may do it different ?
tabetha