I currently have a 4 psi cap that I sourced from SNG. I installed a radiator reservoir / overflow tank to capture the expelled coolant and then have it returned to the radiator as matters cool off. A guy in the local Jaguar club helped me install this system and recommended a Stant cap # 10206, which is what he uses on his Mark 1 3.4 with a similiar system. Researching this cap I find that it is a 7 psi cap and I'm wondering if that bump up in the psi would be OK on My Jaguar Mark 1 with the 3.8 engine ? Thanks,
Schmitty

 

I have a similar system that I fitted to my 3.4s. I have two 7lb caps one on the radiator and one on the expansion tank and I have not had any problems with mine. It has been fitted and running not for three years and I have not had to top the water up in the expansion tank once and the radiator remains full all the time.