C1 Radiator Cap

[Philip P.]

I purchased a 7 pound replacement cap (correct) from Corvette Central and it would not seal. The cap that I have NAPA 7 pound (incorrect) fits tightly, the difference is there is only an upper brass seal on the replacement cap where the incorrect cap has a upper rubber seal. Has anyone experienced this problem. The radiator has the original tanks (copper). 1960 230 hp. The depth of the neck is 3/4 inch.
Phil Porter

[Calvin M.]

Re: C1 Radiator Cap

Phil -

Yes, I experienced the same problem. A reproduction cap failed to seal. I put on an nos, and bingo, perfect seal. That was four years ago and all has been fine ever since.

Cal

[Philip P.]

Re: C1 Radiator Cap

Cal, Thanks for the information, do you happen to recall if the one you have has a rubber or brass seal. I think the reproduction I bought had the top portion to wide more like the replacement but without the rubber gasket. The rubber gasket on the replacement makes up the difference. I would think it was less than 1/16 of an inch but enough to keep it from sealing correctly.
Thanks
Phil

[Calvin M.]

Re: C1 Radiator Cap

Phil, here's a pic. Upper left is the nos, upper right is the repro. Lower left is a later AC 7lb., and lower right is a replacement Stant 7 lb.

Unless you have a nick at the filler neck, a good cap with the metal sealing surface should work fine. As you indicate, a rubber surface (as on the lower right) will compensate for small nicks.

I can't tell for sure why my reproduction cap did not seal properly, but I think the metal surface was not evenly squared up with the neck when tightened.

Cal

[Jack H.]

Re: C1 Radiator Cap

The sealing action isn't taking place at the metal ring that's adjacent to the cap's upper/inner surface. That's there to provide an interference fit for the twist-lock installation action of the cap.

The sealing and overflow venting properties of the cap are achieved by the lower extension components of the cap. The primary seal (cap to radiator orfice) is via the lower unit's outer rubber ring. Overflow/vent action is achieved by the circular metal insert inside the lower ring vs. its opposing spring.

Wipe all of the rubber surfaces clean AND inspect the quality of the mating surface inside the radiator outlet. Everything wants to be clean, flat and ductile for a proper seal.

If the reproduction cap still doesn't seal after clean-up and visual inspection, I'd send it back to the catalog house who supplied it.

PS, if there's a question as to sealing integrity, Stant makes a nice pressure check machine that many auto mechanics have. Snap an adaptor onto the pressure pump/guage and install the target rad cap onto the adaptor.

Push the pump lever and watch the gauge record absolute pressure. Pump to/beyond the cap's 'pop' point and it ought to automatically vent...

[Calvin M.]

Re: C1 Radiator Cap

Thanks, Jack. The rubber surface on the repro looks good, but it is not quite parallel to the cap cover. All else seems good, including the neck, yet it does not fully seal. The nos cap works perfectly (as do the other two in the pic), so I think the canted surface on the repro may be the culprit.

Cal

[Philip P.]

Re: C1 Radiator Cap

The reproduction cap I purchased would not even tighten down. I think the ears may have not been crimped enough I tried to crimp them some but was concerned that it was going to distort the cap. I understand the operation, but the cap never got tight enough to allow any pressure build up. There is not a problem with the replacement stant cap that is on now. There is a NOS on Ebay that I am watching just depends which arm or leg I want to give up. Maybe both!
Thanks for the help.
Phil
Oh I did send it back to Corvette Central.