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Recently acquired my first Corvette, ‘65 coupe, L76. Needs water pump and I’m looking for advice on what to replace it with. Currently has the 30570 casting with ”A” underneath. I’ve seen some replacements that have 1/2” bypass opening but mine is 3/4”. Thoughts appreciated.
I imagine you want a stock or at least stock appearing water pump? I'm not sure if you know the Usual Suspects for parts or not, Zip Corvette shows a pump for 327s but I don't see the bypass size listed. You could contact them and ask.
Thanks to all for the kind words and reference material, very helpful. The car came with original hubcaps but needed tires badly and I was able to find the rally’s so thought I’d change it up for now.
very nice! Guess it matters if you are trying to keep originality...if not, your engine should be like most other small block chevys...I like Rockauto.
Welcome to the forum and that is a nice 65 you have in your possession. Now with the welcome done the following might prepare you for that nap you have been in need of.
If your car engine is not matching numbers and originality is of no concern, your local parts store should be able to source a functional water pump. For instance O'Reilly's has a Masterpro water pump C301350 for $54.99. Rockauto and others have Gates 43106 for $31.89 and up. Both are cast iron and will have a 3/4 bypass top outlet but include a reducer to accommodate a 1/2 outlet. Some forum members have used the 3/4 bypass and modified the reducer and used epoxy on the casting so it looks correct. When everything is assembled the numbers can't be easily seen so unless you strive for judging I don't see the point in paying the Corvette Tax.
If original Chevrolet casting numbers matter to you then only a 3839175 or 3859326 without a casting date and with a 1/2 top outlet will be correct, and correct will be expensive. Expect several hundred dollars for a correct pump. There is some controversy as to when the 326 pump was put into production. Member Critter1 posted he possessed a GM blueprint dated 18 May, 1965. Meaning a 326 pump could not have been made before the blueprint. With that cavete in mind a 326 pump would be correct I think for a late 65 made in Jun or July. One other tidbit of info is I have seen some 326's sold on ebay to claim that only a 326 pump from casting molds 1 to 4 were used on Corvette. I don't know if that claim is verifiable. Refer to this forum thread https://www.corvetteforum.com/forums...-and-64-a.html
If you want a 3839175 pump, source one that does not have a 3839175P casting number. Besides the P at the end of the casting number that pump will have two reinforcement ribs on the driver side of the pump. The 3839175 casting was poured at Flint, MI while the 3839175P was poured at Tonawanda, NY. All C2 small block engines were assembled and came from Flint.
What are the pump differences? Visible difference in the 1963 casting number 3782609 is the 3839175 has a cast flat surface on the front of the top outlet. Any visible or internal differences between the 175 and 326 pumps I can't say as they look the same to me.
You can find on ebay the 175 and 326 pumps that have been rebuilt and have a 1/2 bypass outlet. Be wary some of these have had the 3/4 bypass reduced to the 1/2 NPT size and I would not part with my Corvette Tax money on one of those.
If you just want a pump casting with a 1/2 bypass outlet here are three candidates on ebay, just be sure to verify with the seller that the bypass size is 1/2 NPT and not wrench size. Unless one is already rebuilt you will have to acquire the casting and pay for shipping, $$, source a rebuild kit $, and if you can't perform the rebuild someone capable to rebuild it for you $$, keep that in mind if you look at the second listing. https://www.ebay.com/itm/286338069080? https://www.ebay.com/itm/177319705629? https://www.ebay.com/itm/196411551980?
Now about those ZZZZZZZZZZZZZZZzzzzzzzzzzzz------......
Last edited by Vitaminmopar; Apr 5, 2026 at 03:24 AM.
I think the rebuild of the original pump is the best option. I bought a new pump from the local FLAPS and found it was twisted for lack of better description. When put on a flat surface, there was a ~1/16" gap on one side at the top. Another new pump was the same. I ended up using 2 gaskets on both sides to install the pump without a leak. CHINA SH_T.
Dennis
New old guy
