I'm still having problems with my Valiant. RT66Jim (member here) asked if maybe I'm having a problem with the radiator cap.

My problem is just sitting there it will seal. For 2 weeks with the cap on. I'll fire it up for the first time after putting in the thermostat housing back on and let it fun...no leak. Come out the next day and it's leaking. Once it starts leaking nothing that I do will stop it unless I take it back off. Take it off put another gasket, maybe another thermostat housing and it will do it again.

Well, after Jim said something about the radiator cap....after the first run of the motor getting up to operating temp....I'll let the motor cool down crack the cap and it hasn't leaked since.

There is still a problem.....for me. I shouldn't have to do that. But it's building too much pressure after I run for awhile and the cap isn't able to get rid of it I guess.

Anyways I'm saying this for maybe food for thought.........

Good luck, let us know some of the things that your try please?