thermostat housing GM 3958002

[Tony C.]

Hi
Looking for help with a thermostat housing part number GM 3958002 what is it for.
Thanks Tony

[Joe L.]

Re: thermostat housing GM 3958002

Tony-----

I can't find anything on that number. However, it's a 1969-released part number. Vaguely, I recall that there were a few PRODUCTION-only thermostat housings used during the 69-72 period. I think that both of them were slight variations of the 3877660. Is the 3958002 configured like a 3877660 except for, perhaps, a lack of the accelerator return spring anchor?

[Tony C.]

Re: thermostat housing GM 3958002

Hi Joe
Yes the 3958002 configured is the same as 3877660 except for a lack of the accelerator return spring anchor. Do you think It was used on corvettes big or small blocks.
Thank Tony

[Joe L.]

Re: thermostat housing GM 3958002

Tony-----

I can't say, for sure. However, I fully expect that it could have been used in PRODUCTION for any 69-73 Corvette. Corvettes did not use the accelerator spring anchor for any 1969-73 models. So, Corvettes would be one of the more likely applications of the 3958002 in PRODUCTION. I'd say if you have one on a 1969-73 Corvette and it appears original, I'd leave it there.

Attached is a photo of the GM #3972128 thermo housing. This one was used in PRODUCTION-only for some 1970-72 applications. How does it compare in configuration to the 3958002 you have?

[Tony C.]

Re: thermostat housing GM 3958002

Joe
The one I have Looks like a 3877660 with the 3 webs in the base not solid like your photo.
Thanks Tony

[Joe L.]

Re: thermostat housing GM 3958002

Tony-----

That's about what I figured it would be. I knew there had to be some difference in the castings. You will note that the 3972126 has ONE of the casting "wells" on one side but none on the other.

The 3877660 later, for SERVICE only, lost all of its casting "wells". It retained the 3877660 part number, though, so there must have been a revision to the specifications for the part. The configuration seen on one side of the 3972128 was, apparently, a "presursor" to this much later design change for the 3877660.

I have seen these "well-less" SERVICE-only examples of the 3877660 sell for big $$$ on eBay to fools that don't know that you need to look further than just the cast-in part number for an original configuration part. It's not the seller's fault. They advertise them as "NOS GM #3877660" and that's what they are since the 3877660 is discontinued. So, the part IS new and it is "old stock"---it's just not "old enough stock" to be an original configuration NOS part.