Radiator Cap Mystery

[Bob B.]

Hi all,

Attached are two pics. I have seen the radiator caps with the blue and red on the top before and never paid much attention. When I got one on an old radiator I bought, I noticed the AC partly hidden beneath the red and blue cover, so I decided to take it off. It is just pressed on over the edges of the rivet in the middle.

The red and blue cover says the cap is a 13# RC-22. Beneath is the type of cap we are more used to seeing, but it says 15# RC-26! So, is the cap and RC-22 or an RC-26?

The addition of the red and blue cover seems to be a completely unnecessary manufacturing step since the cap info is already stamped on the main cap. I thought perhaps if they mislabeled a cap, they might use the cover to correct the error. But there are so many of these caps with the red and blue cover that AC's quality control would have to have been horrific.

So, what's the purpose of the cover and why two different part numbers?

Bob

[Paul O.]

Re: Radiator Cap Mystery

Bob what you have maybe the plant had extra top section of the cap in bins.
Then there was a need for and RC-22 cap 13#. So they used the top with a new glue on label reducing the time needed to make a new top section. The first thing I would do is test the cap to see when it opens 13# or 15#. If it opens at 15# and from the stamping of the wording on the cap it is a very rare RC-26 if I remember correctly for a 1965 BIG $ . Can you post a photo of the other side of the cap for the spring and other components this would also help in identify it correctness.

Added photo of an first design RC-26.


Paul 18046

[Bob B.]

Re: Radiator Cap Mystery

Hi Paul,

Here is a pic of the bottom of the cap. I could use some $$$, but the stamping style of the cap is more like the C1 style. I think the mid-60s and later RC-26's are different on top. I know the RC-26 was used on '64 air cars although I'm not sure what the top looked like.

Anyone who knows what the '64 a/c RC-15 cap looked like, I'd appreciate your posting a pic. And your input on the cover vs. the cap mystery is also welcomed.

Bob

[Paul O.]

Re: Radiator Cap Mystery

Bob I most likely have the year I stated incorrect but the photo I posted is of the very rare RC-26. I have better knowledge of C3 and some of the later mid year Rad caps. But the stamping of the early RC-26 is more like an RC-307 which your cap is like and the underside looks like a early RC-26 should appear. My opinion is you have made a very big score here. Hope someone else backs up my thoughts here soon but most of us are here in Old Town Florida Regional Meet so it could take some time.

Paul 18046

[Bob B.]

Re: Radiator Cap Mystery

Paul,

Thanks for the info and enjoy your trip. Wish I were down there, too!

Bob

[Joe L.]

Re: Radiator Cap Mystery

Hi Paul,

Here is a pic of the bottom of the cap. I could use some $$$, but the stamping style of the cap is more like the C1 style. I think the mid-60s and later RC-26's are different on top. I know the RC-26 was used on '64 air cars although I'm not sure what the top looked like.

Anyone who knows what the '64 a/c RC-15 cap looked like, I'd appreciate your posting a pic. And your input on the cover vs. the cap mystery is also welcomed.

Bob

Bob------


The RC-22 and RC-26 caps are functionally identical except for the relief pressure rating. The RC-22 is, of course, a 13 lb cap whereas the RC-26 is a 15 lb cap. Both caps are designed for use with aluminum supply tanks. During the period for which they were originally designed, this meant their only application was Corvette. These caps could have been used for other applications but since they had a higher cost, the other applications used a less expensive cap (e.g. the RC-15) which did not have features designed for use with aluminum supply tanks.

I have no idea why the RC-22 plate was affixed over the cap stamped RC-26.

[Steven H.]

Re: Radiator Cap Mystery

The other applications used a less expensive cap (e.g. the RC-15) which did not have features designed for use with aluminum supply tanks.

Joe, Could you (or anyone) expand a little more on this? What are the features that are different that correspond with an aluminum tank?

Thanks

[Peter L.]

Re: Radiator Cap Mystery

Bob - Based on my experience, the AC radiator pressure caps with the red and blue cover pieces are as indicated on the red and blue cover pieces for the AC radiator pressure cap part number, therefore the red and blue cover piece designates the application and pressure. The red and blue cover piece was to be left in place because as you observed the information stamped on the top of the radiator pressure cap underneath the red and blue cover can be different. As far as I know, there was/is no instruction on the boxes that these radiator pressure caps came in that directed the user to remove the red and blue cover piece and then use the radiator pressure cap based on the information stamped on the top of the radiator pressure cap.

Pete

[Bob B.]

Re: Radiator Cap Mystery

Pete,

It makes sense that the info on the red and blue cover was meant to be the application.

However, given that, my question still is why did AC produce caps with incorrect info and then go through the effort of manufacturing a separate cover with the correct information and then another production step of attaching it? That makes no sense at all from either a production or economic standpoint. Why not just put the correct info on the cap in the first place and forget the cover??

Even if the part number and the pressure ratings on both cap and cover were identical, the additional effort for the cover to give the same info as what is being covered up still makes no sense.

Thanks,

Bob

[Peter L.]

Re: Radiator Cap Mystery

Bob - I agree, but apparently it was SOP back then. While many radiator pressure caps with the red and blue cover pieces are the same desgination, I have quite a few where the the red and blue cover pieces and the stamped information on the cap aren't. It seems like if they were going to put a red and blues cover piece on the cap all they needed was a cap (any cap) to attach the correct underside parts to and to put the appropriate red and blue cover piece on. Interesting approach.
Pete

[Joe L.]

Re: Radiator Cap Mystery

Joe, Could you (or anyone) expand a little more on this? What are the features that are different that correspond with an aluminum tank?

Thanks

Steven------


The differences relate to the design intention to eliminate or, at least, reduce the effects of galvanic (dis-similar) metal corrosion. The primary features of caps designed for use on aluminum supply tanks were an aluminum center rivet and a special insulating seal between the cap and the top of the filler. There may also have been other features which are more difficult to discern. In any event, everything was directed around eliminating or reducing the propensity for galvanic corrosion.

Several years ago Delco discontinued and replaced the old RC-15 with the RC-26. I suppose that at that point in time the cost of producing and stocking two different caps was greater than just consolidating the two. An RC-26 could always have been used in place of an RC-15 but an RC-15 should not be used in place of an RC-26.

By the way, the configuration of the current RC-26 is nothing like the original RC-26 but the functionality is the same.

[Joe L.]

Re: Radiator Cap Mystery

Here's a photo of the current RC-26. I think it's made in India.

[Steven H.]

Re: Radiator Cap Mystery

Joe,
Thanks for that information, I didn't know about that. I have been using an RC-15 on my '64 without any thought about the difference in metals.
Looks like I had better get the right cap after reading this!

Sorry about getting the thread side tracked

[Robert R.]

Re: Radiator Cap Mystery

Steve,
Don't be sorry; this was great info for all that peruse this board.
It's great to learn something new every time you spend time here.

[Timothy B.]

Re: Radiator Cap Mystery

It always struck me as odd that GM used a radiator cap with aluminum parts for the aluminum radiator but the heater core is copper/brass. If I understand correctly the copper/brass will eat the aluminum if galvanic corrosion happens.

I am going through this now with my Mercury Sable that has all aluminum and plastic parts in the cooling system, the heater core is stopped up and no hot heat. There is no way I am installing the aftermarket copper/brass core, the correct Ford heater core is aluminum and I am sure for good reason.