The Stovebolt Site Forums The Shop Area General Truck Talk GMC Radiator relief valve

I've noticed, and read, that the GMC radiators have a relief valve, and the cap is fixed. On Chevys, the cap is vented and no relief valve. My truck is a GMC and has the relief valve. When I took the radiator to service, the guys almost cut the relief valve (dindn't knew what it was, never senn one), but I stopped them. Shall I trust the valve is working properly (it is not stuck) and buy a closed cap or by the vented cap, just in case. If my truck doesn't have the thermostat, do I need to buy it?

If the relief valve works, use it and a closed cap. It won't hurt anything if you use a pressure relief cap.

How do I know it works? I just noticed it is not stuck, as I pointed and that's it. Does it has a spring? The acutal movement is very little. Obviously I can't go to the radiator shop for help.

somewhere i saw a picture of one apart. all it basically is is a cartridge type valve that is held in with a snap ring. they were set for 4 lbs. so get a higher setting cap and run it and see if it works if it does then everythings good. i add a clear hose to the end of my overflows just so they stick out far enough from the bottom of the radiator that i can see the end of it and use it as a telltale as to when the caps or buttons are pushing out fluid.

you should have a thermostat. if you dont then it was removed for some reason. if you add one be prepared for something out of the ordinary. hi collant temp, leaking relief button, blown ranco valve but then i dont know why you would need one at your location. every truck i had that i addded a thermostat to something happened and then i say thats why they took it out. i fix the reason then reinstall and life is good again for a while.

My GMC radiator had the relief valve. I didn't trust it and when I had a new core installed, I had it removed. They also mounted a nice copper drain tube down the side for me. I use a 7 lb cap right now but I really should put a 4 lb one in.

last spring i was at a show and the gasket on my zero cap crapped out. i couldnt get a 4lb johnny on the spot so i opted for a 7lb to get it home. the button wasnt working and by the time i got home the radiator sprung numerous leaks luckily for be ut was at the top at the tank. since then i got it recored and use a 4lb cap since i could find another zero cap along with the 4lb button.

Thanks for the advice. The guys of the radiator shop added a long tube that goes all the way down of the radiator, guess it is a good detail. I'll always have the 4# cap.