I am looking to replace my current (incorrect) radiator cap with a new correct one. I understand it should be a 15lb cap but some I see are RC15 and others are RC26. What is the difference and which is the correct 15lb rad cap for my car, RC15 or RC26? Mine has a 400ci 4bbl, no AC or overflow tank.

 

The RC15 is correct if you have a stock type copper radiator. The RC26 was the same cap but designed for the Corvette with an aluminum radiator. I suspect it has an aluminum coating to prevent galvanic corrosion where it clamps to the filler neck. If you have an aftermarket aluminum radiator, use the RC26. And as you probably know, there was no factory overflow tank in 1968.

 

Great! Thank you once again Joe for setting me straight on this stuff. I just ordered the RC15 cap from Fussick.

Thanks again!
Phil

 

Since it's been asked and answered already, if I may hijack.


For those of us with 68 and older cars that WANT a factory appearing or "stealth" overflow tank, what are our options? Can the 69-72 tank work? Is there a black thing that looks like the side of the radiator but actually is a reservoir? Must I go rat rod and use a Jack Daniels bottle?

 

This is kind of stealthy. Plastic... and widely available. Definitely better than a coke bottle.

 

I'm going to try a Dorman 603-001 Coolant Reservoir Bottle and mounted behind the RH headlight area on a custom bracket. Can't go wrong for $7. You could paint it black to make it more stealthy.


Don't forget to use a RC27 radiator cap if you want the recovery function to work. Easy way to remember is just get a cap for a 75 Cutlass.

 

I prefer road puke!

 

I used that reservoir, it worked well.

 

That may work. My other old A body has, I think, a Buick tank wired to the frame horn for a recovery tank.