71 lt1 water outlet

[Robert P.]

I need some help with correct part no. The book states part no. 3877660 for 68-73 small blocks [ water neck]. A friend of mine has 71 lt1 he bought new,all original. His part no. on the water neck is 3972128[ we can't find any info on his] Can Anyone tell me the correct part no. Thanks for any help. Bob

[Phil P.]

my 72 lti has 3972128 original *NM*

[Joe L.]

Re: 71 lt1 water outlet

Bob-----

I believe that it's correct for your application. The GM #3972128 is a PRODUCTION-only thermostat housing that was released in 1970. For Corvettes, I believe that it was used on some 1970 through 1973 Corvettes, both big block and small blocks. I believe that the 3877660 predominated during this period, but the 3972128 was alternately used.

I believe that the two housings are identical EXCEPT for the fact that the 3972128 deletes the triangular-shaped extension with hole that extends from the base and is used, for some models, as a mounting point for an accelerator return spring. It is not so-utilized for any Corvette, so a thermostat housing with or without such an extension will work perfectly well.

Please let me know, though, if the 3972128 housing that you have does or does not eveidence the feature I described.

[Phil P.]

72 lt1 "128 hsg" i have no triangle *NM*

[Robert P.]

Re: 71 lt1 water outlet

Joe, the 3972128 that is on my friends LT1 does not have the triangular extenson.Would either part no. be correct for my LT1? Bob

[Joe L.]

Re: 71 lt1 water outlet

Bob-----

My opinion is yes. However, I have forgotten if it is recognized in the current edition of the JG.

[John H.]

Re: 71 lt1 water outlet

The 660 housing has the triangular provision and hole for the return spring.

[Joe L.]

Re: 71 lt1 water outlet

John-----

Yes, I was sure about that but I just wasn't certain if the 3972128 lacked it. I was pretty sure, though, that was the difference between the 2 outlets and, from what's been reported, it looks like that is what the difference is.

From 1966 to 1970, the 3877660 was used for all applications requiring this configuration outlet. For 1970-73, apparently the 3972128 was used alternately with the 3877660 for those applications not requiring the pull back spring mounting point on the thermostat housing (which included all Corvette).

The 3972128 was a PRODUCTION-only piece; I can find nothing to indicate that it was ever available in SERVICE. Actually, it surprises me that it was ever released and used for PRODUCTION. For the minimal savings-per-piece that it would have produced, you would think that it would not have been worth doing, especially considering the extra bit of complication that it would have generated for the engine assembly line. Perhaps it was a case, though, in which the return spring mounting of the '660' actually interfered with something for some 1970-73 application which necessitated the release of an outlet with no such provisions. Once released, it could have been used for any application not requiring a pull back spring mounting on the outlet.