I found a 72 Olds 350 in the boneyard today ( in a Chevy of all things... ) and noticed it had a thermal vacuum switch screwed into the front passenger side water port on the intake. It also had an electrical connector on top of it. I have an idea what this switch was used for but I'm not 100%sure. So what's the skinny in this thing?

 

Got a picture of it?

 

Trans Controlled Spark advance combined with thermal control. VHTF unbroken. Hard to remove w/o damage. 6-pt crowfoot might do it. Not terribly useful. I guess big dollar resto folks will pay well for an NOS one, just to have all the "right" pieces in place.

Consult your service manual for all the gory details.

 

yep I'd try to grab it, those are hard to come by and some folks would like to have it even if it doesn't work. yes NOS would bring big bucks but some folks would be willing to pay a lot less for a used one.

 

I get the vacuum part of it, but what about the electrical? The way I'm seeing it is, you get no vacuum advance to your distributor until the TVS heats up enough to allow the vacuum to go through. That makes sense to me, but the electrical part has me stumped. I'm assuming it functions just like for vacuum above; it allows current to flow through only after the engine warms up. What uses that?

My friend said he might buy the whole engine.

 

This might help (from the 1972 Chassis Service Manual):





- Eric

 

The electrical connection went to the tranny. There was a switch that senses high gear. When in high gear, the disty advance switched to ported vacuum. When in low gears the disty was from manifold vacuum. When in high gear, if engine temp exceeded 210*, the disty was given manifold vac to help the engine run cooler.
This device was only to help reduce Nox emissions. Bypassing it often improved drivability so they were often disconnected or removed. If in good shape, keep it and test it - might be worth some $$ to a restorer.

 

Au contraire my friend. I have a couple of these kicking around that were very easy to remove. They clean up very well. The only part that might get brittle is the plastic around the electrical connector

 

Yep, that's the switch and thanks for the explanation. I didn't realize it was so involved. If my friend gets the motor, I'll probably nab that switch from him and sell it to someone who may need it for a resto.