Thermostat Housing Switch

[71CHEVYSHORTBED402]

Just curious if anyone still has the complete assembly, and if you do props, does it work. I may never assemble one, but I'm wondering, what do the lines route to? Thanks.

Looks like this, perhaps

[ray_mcavoy]

I believe that's off a newer engine ... probably mid/late 70's or 80's ... not original for 67-72.

Those thermal vacuum switches (TVS) were used to control a variety of things ... like EGR valves and other emissions equipment.

[kwmech]

Originally Posted by ray_mcavoy

I believe that's off a newer engine ... probably mid/late 70's or 80's ... not original for 67-72.

Those thermal vacuum switches (TVS) were used to control a variety of things ... like EGR valves and other emissions equipment.

Sometimes even the vacuum advance on the dist.

[71CHEVYSHORTBED402]

Originally Posted by ray_mcavoy

I believe that's off a newer engine ... probably mid/late 70's or 80's ... not original for 67-72.

Those thermal vacuum switches (TVS) were used to control a variety of things ... like EGR valves and other emissions equipment.

Pretty sure that housing is 336790, which shows for a number of truck years, including 71-72. But the switch might be different.

Might be worth mentioning the housing I removed from my 1971 is cast iron, stamped 1595. It's vintage IMO, though I'm not sure it's truck original, and it doesn't have female threads for a switch.

[ray_mcavoy]

Originally Posted by 71CHEVYSHORTBED402

Pretty sure that housing is 336790, which shows for a number of truck years, including 71-72. But the switch might be different.

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.

[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.

[RichardJ]

I use one of those to control one of the electric pusher fans. The switch is a 208* switch from a Honda Accord. I had to make the thread adapter. The other fan is controlled by the AC. Both fans are from '90s Cadillacs.

[Palf70Step]

My 81's 250 6 had that. Mostly for smog stuff. I think I still have them. I've seen them use the thermostat housing for a seperate temp sensor for electric fans.
Ibelive the 6 stuff will work on small block also.

[special-K]

That is a newer housing. 67-72s didn't have that stuff. A story: I used to stop in the my Chevy dealer on a regular basis to have the parts guy look up parts availability and order what was available. One day I had him check 69-72 truck steering wheels. "It shows they are available but only in black". I couldn't get the words "Order me up one" out of my mouth fast enough. It came in as the current '80s truck steering wheel. That's when I learned GM's concern for supplying parts for their vehicles is offering what will work, not what is correct for a restoration. They print supplemental parts books to list superceded parts numbers for depleted parts numbers

[71CHEVYSHORTBED402]

Thanks for the education

I forget or never knew. Original housings have a hole for a spring I guess, what for?

[Steeveedee]

Originally Posted by 71CHEVYSHORTBED402

Thanks for the education

I forget or never knew. Original housings have a hole for a spring I guess, what for?

That was for the throttle return spring on a lot of vehicles.

[special-K]

I really like those housings with the tab & hole for return spring. I keep those when I find them

[KQQL IT]

Some opened/closed the hot air stove door in the air cleaner.