Thermal vaccum switch

[BigBlueIron]

Anybody every use one on purpose? I never have. But I'm thinking it might solve my drivability issue. Engine is generally cold blooded for whatever reason or another and I like to hop in this thing and go, its sluggish almost being held back at low throttle try to give it some more and a backfire through the carb. Only when cold, when warmed up absolutely no issues. Vac advance is bringing in to much timing when cold so thinking adding one of those thermal switches might be the trick?

[thatdarncat]

I had a basic understanding of how the stock system worked, and had seen it helpful in action on hot days stuck in traffic with my ‘78 Bronco. When I did the engine swap to a mild 460 in the mid ‘90’s I duplicated the thermal vacuum switch set-up on the 460. I was happy with the performance. I’d say give it a try.

[GerryP]

There are two types of thermal valves:

1) There is a valve that blocks vacuum advance to the distributor when the engine is cold.  This type valve helps the engine to warm up faster since the later burn puts more heat into the coolant.  This is an emissions control function that has been around since the 1960s.  My '67 Fairlane California car had one.  It is a Carter control box that controlled the vacuum advance based upon a thermostatic sensor inserted into the radiator fins.  I still have that in a box.

2) The second type valve has three hoses running into a thermostatic valve.  On hose in the middle goes to the distributor.  The other two hoses are both vacuum hoses from the carburetor; one hose goes to ported vacuum.  The other goes to manifold vacuum.  The way this valve works in that when the engine temperature is normal, the vacuum advance gets ported vacuum.  If the engine begins to overheat, the valve moves and closes off ported vacuum and picks up manifold vacuum, which immediately advances the ignition which raises the idle RPM and makes the ignition burn occur earlier to cool the burn into the exhaust and keep less combustion heat from going into the coolant.  The higher idle speed moves more coolant through the radiator and runs the fan faster.