ORIGINAL R 26 EXPANSION TANK CAP

[Rob A.]

I noticed there are aways several original R15 caps on ebay for big blocks, but hardly see any original R26 caps for small blocks. I would have thought it would be just the opposite. Anyone happen to have an idea why?

[Patrick H.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Part of the reason is that the RC-15 was also used on small blocks with AC. So, as time went on, more and more Corvettes used an RC-15. In addition, the RC-15 was manufactured for more model years in "Corvette" configuration than the RC-26.

I also highly suspect the RC-15 had other uses including passenger cars, which would account for its popularity.

Also, realize that there are 3 distinct variations of the RC-15 cap, and the cap in many auctions does not match the cap used in the year the auction is describing. For example, they know they'll get more money if they say "RC-15 67 big block," but the cap may not be correct for a 67 but rather a 71. More to follow in the Restorer....

Patrick

[Peter L.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Patrick - If your reference to small blocks with AC using the RC-15 is in reference to GM passenger cars in general, the comment is correct but with regards to small block Corvettes with AC my experience is that the appropriate AC cap for the expansion tank is/was the RC-26. The application of the RC-15 as far as Corvettes is/was concerned was on BIG BLOCK Corvettes with and without AC and without the aluminum expansion tank. Pete

[Patrick H.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Pete,

Small block AC cars from 68 onward did not have an expansion tank. The tank is integrated into the radiator, and they used the RC-15 cap. So, the only small block cars from 68 on that used an expansion tank, and therefore the RC-26, were the non-AC cars. Since AC became much more prevalent over the 68-72 era, the caps became much more common on Corvettes and I suspect GM products in general.

Your statement is correct regarding small block pre-68 cars, but as my brain stays in "70-72 mode" despite all my radiator cap research in front of me I generalized my statement in error.

Patrick

[Joe L.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Pete----

The RC-15 was also used for some small blocks in the 1968-72 period. These included 1968 with C-60 and/or THM, 69-72 with C-60 and/or THM, many 1969 with L-46, all 1970 with L-46, and most 1970-72 with LT-1 (except, possibly, some early 1970 and 70-72 ZR-1).

[Peter L.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Patrick/Joe - Thanks for straightening me out on the post 1967 Corvettes, as usual I get stuck in the pre-1968 era.

And Patrick you are correct on the use of the RC-15 across the GM product line especially on AC car. In fact the RC-15 has a long history as Joe can probably elaborate more on but I see applications all the way back to1957 for Buick, Oldsmobile, and Pontiac w/ AC and 1960 for Cadillac w/ AC on an old box I have. The stamping on the top of the cap has gone thru several changes, so the comment on alerting folks to beware of what year the cap's application is for is most appropriate (let the E-Bay buyer beware). Pete

[Patrick H.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Pete,

Yes; in fact, the first design RC-15 was used ONLY on passenger cars.

Patrick

[Joe L.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Pete-----

Yes, the RC-15 has a very long history. Basically, it was, for many years, THE AC radiator cap for 15 PSI systems with copper/brass radiators. In fact, that's where the "RC-15" designation comes from. "RC" was (and remains) the AC-Delco prefix for radiator caps and "15" referred to the PSI rating (that part of the system was long-ago abandoned when cap configurations proliferated).

The RC-26, on the other hand, was a Corvette-only piece. Basically, it's identical to the RC-15 in fit and function. However, it has special provisions for use in contact with aluminum radiators or aluminum supply tanks in order to minimize galvanic corrosion. The RC-26 could ALWAYS have been used in place of the RC-15, but not vice-versa. The reason that both existed was that the RC-15 was less expensive since it didn't have the anti-galvanic corrosion provisions. In PRODUCTION, GM obviously didn't want to use a more expensive radiator cap when the vast majority of the applications didn't require some of its features.

Within the last several years, though, the RC-15 was discontinued and replaced by the RC-26. So, now all of the non-Corvette applications that originally used the RC-15 get to use the once Corvette-only RC-26. In later SERVICE, parts consolidation efforts bring this sort of thing about. Since the RC-26 can SERVICE all RC-15 applications as well as, obviously, all RC-26 applications, it only made sense that the RC-15 was the one to "die" while the RC-26 "lived on". I don't think that it's "immortal", though. Its day will come.

[Peter L.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Joe - Thanks for the discussion. BTW, if the RC-26 doesn't "die," it will surely won't look the same and it will probably be made of plastic!!!!!!!!!!.. Pete

[Dennis D.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Joe

Are far as the 70 L-46, although mine has it, I thought the expansion tank/ alum rad wasn't used, or are you referring to the R-15 cap being used on the copper cored radiator?

[Joe L.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Pete-----

The RC-26 has already changed considerably from its original configuration. I would not be surprised, at all, to see further change. GMSPO has "0" interest in "NCRS/NCCB-correct" parts. Their primary interest is in selling parts which will SERVICE the application. They regard "updated" parts as a "plus", and the vast, vast majority of customers would regard updated parts as a "plus", too. Those of us interested in restoration might regard updated parts as a "minus", though.

[Joe L.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Dennis----

I may have "overstated" the case for 1970 L-46. MOST 1970 L-46 used the copper/brass radiator with integral filler cap and no supply tank.

[Patrick H.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

Yes, I have the blueprints for the current RC-26, and it is NOTHING like the originals in appearance.

Wonderful functionality, but totally noncorrect appearance.

Patrick

[Bill Stephenson]

Re: ORIGINAL R 26 EXPANSION TANK CAP

-------My 64 Grand Prix came with an R-15 from the factory..........Bill S

[John H.]

Re: ORIGINAL R 26 EXPANSION TANK CAP

So did my '69 Z/28, and it's still there - the Camaro crazies are paying $600 for them on eBay; nope, not gonna part it out