53-55 Radiator Cap question

[David L.]

My July 1955 Corvette Parts Catalog lists GM # 850778 (in Gr. 1.203) as the part number for the 53-55 (exc. V8) radiator cap and is described as "pressure type" and "chrome". Further research indicates it is a 4 PSI cap. I believe that it is an AC cap. Is this the only cap installed on the 53-55 assembly lines?

Pictured below is a NOS cap that I found at a swap meet last Sunday. It is stamped with the number "4" (4 PSI) and I believe that it is made by the Stant company. It is very similar to the 3708174 cap (7 PSI) shown in Noland Adam's 53-62 restoration book (57 Corvette) on page 150 except for the pressure rating number.

Dave

[Troy P.]

Re: 53-55 Radiator Cap question

All for 6 cylinder Corvettes were chrome and made by AC. AC is indicated on the cap and the box along with the last three digits of the part number.

I believe the replacement 4# AC cap is an RC-1 or RC-2. Can't recall which.

[Chris S.]

Re: 53-55 Radiator Cap question

Here is a correct 53-55 #4 radiator cap - note how the #4 and the 778 are on one end - stamped in - chrome plated - part number 850778
there is several different configurations of the #4 and 778


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[Troy P.]

Re: 53-55 Radiator Cap question

BTW seems to me the RC 1/RC 2, whichever is the 4# replacement cap, is stainless steel rather than chrome plated. It can be buffed to a fine shine and makes a good replacement. Not factory original obviously but a nice one to have until you find the right one.

[David L.]

Re: 53-55 Radiator Cap question

Enclosed is a photo of an original 1953 Chevrolet 6 cyl. 4# "501" AC radiator cap that has been in my radiator cap collection for at least 30 or 35 years. Since the cap probably has no real value I buffed up the cap to make it look like it is chrome plated. According to my 1957 Chevrolet Parts Catalog (March 1957) this cap is GM part # 850796 and described as "pressure type (dbl. ear-marked 501)". The 53-55 Corvette 6 cyl. cap is GM part # 850778 and is described as "(pressure type - chrome)". It seems to me that the "501" cap is essentially the same cap as the "778" cap except for the chrome plating and the stamped number.

Back in 1987 I found an NOS RC-2 GM # 850796 4# cap at a swap meet but sold it a few years later.

According to Chevrolet Parts History GM # 850778 was replaced with GM # 850796 in Jan. 1965.

Dave