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Please ID this water pump for me. It's currently attached to a 66 327/300. In large letters I see GM 21 and in smaller numbers I see(as best as I can) 8782808. Another set I see is L187.
I believe that the number is 3782608; 3s, 8s, 9s, and 6s are easy to confuse with casting numbers.
The GM casting #3782608 water pump was used for many 61 through 1970 Corvettes as well as many 61-68 passenger cars. It is an internal-bypass design and has no threaded boss on the top for external bypass. For Corvettes, it was used for all 62-70 models with small block engines and cast iron intake manifolds. This is a small bearing, 5/8" shaft waterpump as was used on all pre-1971 small blocks.
Because of the confusion which casting numbers present, it is also possible that the pump is a 3782609. If so, this pump has provisions for an external bypass which consists of a large boss on the top which is drilled and tapped for 1/2" NPT fitting. The '609' casting was used primarily during 1961 and 62 for engines with aluminum intake manifolds. I don't recall that it was ever used on a C2.
Your casting date would indicate a 1967-cast water pump. The '608' casting was not in production as early as 1957 and was out of production by 1977, so yours pretty much has to be 1967.
By the way, the '608' casting would be the correct casting for a 1966 with 300 hp engine. However, this particular casting is not dated correctly for the car since it was cast on December 18, 1967. Likely, this pump was originally used on a 1968 model Chevrolet car or light truck, possibly a Corvette, or was originally a SERVICE water pump manufactured about that time. Virtually all 1968 Chevrolet small block engines used the '608' water pump casting, including ALL 1968 Corvette small blocks.
Yes, the '608' casting water pump was used on most 61-68 Chevrolet passenger cars with small blocks with or without A/C. It was also used on most 63-70 Corvettes with small blocks and A/C. The only exceptions were 65-67 L-79 with A/C and those few 1965 L-76s equipped with A/C.
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