when i turn my 91 cherokee off i think the radiator cap blows off every time almost well thats the only thing i can think of cause i had a cooling systems check i had no leaks but i had hydrocarbons in my fluid but i had it cleaned out and my cap was failing to blow off at the appropiate psi it was blowing off at 2 psi so i got a new one set for 13 but it still leaks and i dont know where from ? any feedback anybody elses **** do this its quite irritating

 

Is it a closed system?? Is it the plastic bottle?? Are the threads good on both the bottle and the cap? If so it could be an overpresure of the cooling system due to exhaust gases getting into the system caused by a faulty head or gasket.