aluminum water neck

[Warren F.]

Is this the correct part # 3958002 for a 1971 LS-6 intake manifold application, or should it be part # 3877660?

3958002 is cast on to the flange portion of the part, while 3877660 is cast into the neck portion of the part.

Also the 3958002 part has indented areas around the bolt hole positions, 3877660 does not have these voids.

[Joe L.]

Re: aluminum water neck

Warren------

"Officially" the GM #3877660 is the thermostat housing used for 1971 with LS-6. The 3877660 was manufactured with the part number embossed on both the neck and the base, although by 1971 I think that it was pretty much found just on the neck. Also, the 3877660 was manufactured both with and without the base "indentions" that you described. However, those originally used on all 1966-72 applications using the 3877660 DID HAVE the indentions. The other style are SERVICE only.

I would not rule out the possibility that the 3958002 was used for some applications, including the LS-6, during the 1970-72 period. I don't have any documentation for this, but I think that it's very possible. I don't understand just how this 3958002 "fits into the picture", but I've herad of other cases in which this thermostat housing was found on what were believed to be unmolested, original installations.

[Warren F.]

Thank you, Joe *NM*

[Harold M.]

Re: aluminum water neck

Warren, Mine is the 3877660 stamped on the neck only, and no doubt original.