Thermostat Housing Switch

[71CHEVYSHORTBED402]

Originally Posted by ray_mcavoy

Yes, the GM parts catalogs could very well list that newer style thermostat housing as a service replacement part for earlier years. The installer would simply have to put a pipe plug in the unused hole.

In fact, GM did that from the factory (pipe plug in that hole) on mid/late 70's trucks that were over the GVW threshold to be considered "heavy duty" and didn't require as much emissions equipment as cars & lower GVW trucks.

I see. I searched 336790, and it comes up on vehicles from 1966 to 1979. Are you saying 67-72 came without female threads? As I mentioned earlier, the cast iron pulled from my truck was without threads.

[ray_mcavoy]

Originally Posted by 71CHEVYSHORTBED402

Are you saying 67-72 came without female threads? As I mentioned earlier, the cast iron pulled from my truck was without threads.

I can't say with 100% certainty, but I don't think 72 & earlier thermostat housings originally had that female threaded hole in them. I've seen both iron and aluminum versions of the housings without the hole ... I don't know if that was something that changed after a certain year or if it varied by application.

[leftybass209]

The 350/350 in my 72 had the original intake, water neck, and quadrajet, and was an A/C and CA emissions born truck, but no extra provisions in the cast iron water neck.
I only lend the extra info because as we've found out on these trucks before... sometimes it's just a goofy combination of parts ordered that requires different parts like this.