Big Block Thermostat Housing

[John R.]

I have two different examples of the thermostat housing for my 67 L36 big block. Both are part number 3877660. The one presently installed has the part number on the neck. The second one has the part number on the base which I would call the flange. The Judging Guide indicates the second one is correct but a number of people have told me that the first one is correct and the second one is a service replacement. Both housings are indentical with the exception of the location of the part number.

[William C.]

Re: Big Block Thermostat Housing

You did not mention the yaer, but the number on the flange was pretty standard practice in the early and mid-60's. Most of the number on the neck esamples i have removed from manifolds were of the late 60's early 70's vintage. There is as always the possibility of some overlap in usage.

[John R.]

Re: Big Block Thermostat Housing

The car is an early production 67. Engine assembly date of 09/21/66. Sounds like it falls right in the middle.

[Rob A.]

Re: Big Block Thermostat Housing

The # is on the flange on original housings. {I have an early '67 (build date 1/67) with # on the flange). It is my understanding that those with the # on the neck are either service replacements or reproductions.

[William C.]

Re: Big Block Thermostat Housing

More to the flange side of things, I first saw the neck part numbers on Iron intakes from Chevelles circa '68-69. If in doubt, I'd reference the Jusding Guide and follow it since you have both available.

[Everett Ogilvie]

Re: Big Block Thermostat Housing

I have two early '66's (built Oct '65) both with the number on the neck. My late '66 (May 31) had the number on the flange. You will get more opinions on this than you ever wished for (actually there are only two opinions either way). There is research going on right now as part of some '66 Judging Guide edits, with GM part drawings, which might help pinpoint any running changes.

I have a friend who once saw a box of these necks in a wrecking yard - about 100 total and they were 50/50 between the neck and the flange (he intentionally went through the box to make the determination). It is doubtful that a box in a wrecking yard was half full of reproductions...

In my opinion, this "box in the wrecking yard" indicates that both styles indeed came from GM. The questions are; was one an early style and the other a later sytle, OR were both used at the same time (for some period)?

[Joe L.]

Re: Big Block Thermostat Housing

John----

These GM #3877660 thermostat housings were used on a HUGE number of applications in the 66 to 72 period. It was, by no means, a Corvette-only item. These housings were a die-cast aluminum piece and, considering the quantity needed for PRODUCTION purposes, I'm sure that there were MANY molds used. There were likely more than one supplier, too. I feel pretty confident that this was not an in-house, GM manufactured piece. So, I really think that either could have been originally used on your car. I would tend to think, though, as Bill mentioned, that the flange part number would be the most likely.

One other thing, however: you didn't describe the piece beyond the location of the part number. Original '660' thermostat housings have the casting depressions adjacent to the bolt holes at the base. If your thermostat housing does not have these depressions, then it's DEFINITELY a SERVICE replacement from a much later era. I don't think that any of the "non-depression" outlets were EVER used in a PRODUCTION car, Corvette or otherwise.

[John R.]

Re: Big Block Thermostat Housing

Both thermostat housings have the web-shaped casting depressions adjacent to the bolt holes. Both housings are almost identical although the molding markings are slightly different. Interestingly, the housing with the number on the flange has some internal "bubbles" or "blisters" in the aluminum casting. The 67 Judging Guide states that the housing with the number on the flange is correct, but it appears that there is a real split of opinion on this one.

Thanks to everyone for their opinion.

[John H.]

Re: Big Block Thermostat Housing

I don't have the 660 drawing, but I understand from Paragon that it shows the part number on the neck (at least as of the drawing's last change level); there may have been an "optional" location shown as well (which was common practice to accommodate suppliers' tooling designs), and that would explain the apparent preponderance of housings with the part number on the flange. Good research subject.

[John R.]

Re: Big Block Thermostat Housing

I have two examples that look identical with the exception of the location of the part number. Perhaps this would make a good subject to research for a Restorer article.