1966 427 425HP Radiator Cap

[Joe T.]

I have seen a few advertisements and pictures of original and after market 1966 427 radiator caps that look different. Can someone please provide pictures of an original (both top and bottom) and GM part number for a 1966 427 425HP with a mid April build date radiator cap?

Thank you,
Joe T.

[Patrick H.]

Re: 1966 427 425HP Radiator Cap

Reproduction:

https://www.ebay.com/itm/Radiator-Cap-RC-15-New-Licensed-GM-Correct-Reproduction/261667738909?hash=item3cec9cd51d:g:wFIAAOSwg3FUbAZL:sc:USPSPriority!49424!US!-1

Original:

https://www.ebay.com/itm/Original-1966-1967-Corvette-Chevelle-Camaro-Nova-GTO-RC-15-Radiator-Cap-restored/253916044012?epid=1023076146&hash=item3b1e935aec:g:84YAAOSwe~BbtnPD&vxp=mtr

They are long-discontinued by GM, and the part number is not on them. I don’t know it offhand but I don’t think it makes much difference.
I believe that yours would have the depression in the center of the rivet like what is shown on the (restored) original above.

[David L.]

Re: 1966 427 425HP Radiator Cap

I bought this cap at a swap meet years ago for my 1970 Camaro SS350 project.
Dave

[Ara G.]

Re: 1966 427 425HP Radiator Cap

Dave, I think that's a later style rad cap with it having the flat brass rivet. 66/67 should have a dished rivet.

[David L.]

Re: 1966 427 425HP Radiator Cap

Ara,
You are probably right as that cap is for my 1970 Camaro SS350.

Below is a photo of a cap from an original 1967 Corvette L36, C60 VIN: 17XXX. I forget where I got this photo, a NCRS member, I believe.

Dave

[David L.]

Re: 1966 427 425HP Radiator Cap

I think that the RC-15 cap in the photo below is is an early version of the RC-15 cap. It's been a few years since I studied these caps.
From Chevrolet Parts History:
GM # 861050 replaced by GM # 3886273 in Jan. 1966 which was replaced by GM # 6410456 in March 1973 which was replaced by GM # 861050 in July 1977. What goes around comes around.
Dave

[Ara G.]

Re: 1966 427 425HP Radiator Cap

Dave,
That looks spot on for what we would expect to see on a 66/67 Big Block. Script looks good, rivet looks good, arrows look good, etc...Cheers and Happy New Year!. ARA
Regarding post #5.

[Patrick H.]

Re: 1966 427 425HP Radiator Cap

I would have thought that Dave's last cap was earlier than for a 66, same as what he suggested.

[Tom D.]

Re: 1966 427 425HP Radiator Cap

Note the "thickness" of the letters stamped by AC on the originals, vs. the "thinner" and "crisp" stamped letters on the reproduction cap.