1974 Thermostat Housing with & w/o TVS: JL - what do you make of this?

[Tom R.]

Hoping Joe Lucia sees this and can provide some insights but as we revise the 73/74 manual, we come across these production anomalies and the GM# 336773 thermostat housing is such a part.

In 1974, TVS-EGR is introduced but we have owners of original cars with the part number but different configurations for both TVS and non-TVS functions.

A Nov 73 built 1974 L82 M21 shows thermostat housing with part number of the flange. In contrast, an LS4 M40 (April 1974) shows 336773 with TVS and same part number on the flange. Most unusual.

Am I missing something here?

Team members refer to an earlier post regarding 1973 thermostat housing 3972128 vs. 3877660, so we use that as reference base.

https://www.forums.ncrs.org/showthre...ct+Part+Number

[Joe L.]

Re: 1974 Thermostat Housing with & w/o TVS: JL - what do you make of this?

Tom------

I have used examples of both of the thermostat housings you picture. You have discovered an anomaly that I discovered quite some time ago and have never been able to explain---two completely different parts with the same casting number.

What must have happened here is that the drawing and specs for the casting were changed with no change of part number. Since the functionality of the part changed, in the vast majority of cases GM would have just assigned a new casting number to the revised part. For whatever reason (and, I'll bet there's a very interesting story behind it which we'll likely never know), this did not happen.

[Tom R.]

Re: 1974 Thermostat Housing with & w/o TVS: JL - what do you make of this?

I guess we're special then? LOL