Acv 306 vs 307 Radiator cap

[Dave S.]

All 306 radiator caps I have seen are aluminum. Sometime in mid production 1961 the caps were changed to 307 and that cap was used into 1964. I have what appears to be an original 307 that is made from steel. Was the 306 the last of the aluminum caps and were all 307's made from steel.???? The 61/62 Judging Guide is silient on this. Any help is appreciated.

[Mike E.]

Re: Acv 306 vs 307 Radiator cap

That's exactly what I've seen, Dave. And the 306 had more of a yellow/green hut to it, even though it was aluminum. I haven't quite figured that one out, but I'm not a metallurgist.

[Dave S.]

Re: Acv 306 vs 307 Radiator cap

Mike,

Thank you. It seemed funny to me that the 61/62 TIM & JG didn't mention this change as it occurred during 61 production.

[Christopher R.]

Re: Acv 306 vs 307 Radiator cap

Not sure, but I thought the 307s were stainless steel. I thought the change was made by Chevrolet because of electrolysis concerns with a steel cap and an aluminum radiator.

[Dave S.]

Re: Acv 306 vs 307 Radiator cap

Chris,
My 307 holds a magnet so on that basis I assume its steel.

[Peter L.]

Re: Acv 306 vs 307 Radiator cap

Dave/Chris - The original 307 radiator caps were zinc plated steel. The large washer directly under the cap was aluminum and then there was a large fiber washer. The rivet was also aluminum. Other radiator cap assemblies like the RC-15 and the RC-26 came out initially as zinc plated steel and then in the late 70s or 80s these radiator cap assemblies came with a stainless steel cap; but I do not recall seeing a version of the 307 with a stainless steel cap. Pete

[Joe L.]

Re: Acv 306 vs 307 Radiator cap

Pete-----

There was never a version of the '307' with a stainless steel shell. The '307', a 13 psi cap, was discontinued and replaced by the 15 psi RC-26 in April, 1974. This was well before the advent of the stainless steel shell caps. Consequently, there never was a stainless shell version of the '307'.

[Patrick H.]

Re: Acv 306 vs 307 Radiator cap

Joe,

The RC-33 came out in 1973 with a stainless steel shell. So, April 1974 is not prior to the advent of that form of cap. But, I highly doubt they changed the 307 to stainless.

Patrick