I would like to know if my '78 F-150, 400 motor, non-CA emissions truck originally contained a PVS switch on the thermostat housing(or anywhere else). There are two plugged holes on the housing. And, if it did, was the switch a three port switch?

AND, what was the vacuum hose routing on the switch?

 

I know that my 79 351M way back when had it. You would probably need more info to figure if it had a ported vaccum switch or not. What is the reason? Do you need to take an emmision test or something?

 

My 78 Bronco 351M has one TVS on the thermostat housing, and the second hole is plugged. The TVS is a three port, but I'm not sure how it was utilized from the factory. A possibility is that one port connected to the intake port (between the carb and thermostat housing), another port connected to the carb vacuum advance port, and the third port connected to the distributor vacuum advance.

This setup would give no vacuum advance when the engine was cold, normal vacuum advance at normal operating temperature, and manifold vacuum when the engine was overheating (the manifold vacuum would cause a higher idle, thereby cooling the engine off).

This is just my best quess on the vacuum routing.......

 

I was thinking that it went to a ported vacuum, manifold vacuum and the vacuum advance and would advance the timing when cold to help it run better and warm up faster for lower emissions.

 

U didnt say if it had a air pump or not. most mods ive worked on had 3 port pvs.one coming from the intake one going out to the charcole box the other to the egr valve.hope this helps.I send most of that equipment to the landfill an hour after getting a new "old" henry.

 

Thanks for the replys. The engine came from the factory without catalytic converter and without an air pump. I think the 78 Broncos had the air pollution control(catalytic converter) because they were rated at 6000 lb GVW, whereas the F-150 (6050 GVW) did not. I was asking because I read that the ported vacuum switch also assisted in overheating situations by changing from ported vacuum to full manifold vacuum at low idle situations.

I have an overheating problem(like a lot of people) but not at idle.

What I have done to solve at this point: new water pump, new antifreeze(mixed at 60/40 - will adjust to 50/50 to see if it helps), new 180 Deg F Thermostat(Yes, it does open @ 180 deg F), new thermo clutch fan, burped air out of heater core and radiator, new radiator hoses(no kinks in upper or lower hoses). Also the original shroud is still in place and in good shape.

The overheating problem started BEFORE all the above-mentioned work was done. I am waiting for a new radiator at this point, and will post after the radiator is installed with the results.

The engine gets to the 'p' in Temp during long gradual grades. Using an infrared thermometer, I measured the temp at the top of the radiator at 220 degF and the bottom of the radiator @ 180 degF, but the temp was measured after pulling over to check the temp. The temperature drops quickly after slowing down. The engine has only boiled over just once during a 7% grade pull with a camper trailer

 

Sounds like maybe the radiator is partially clogged and at higher speeds, the coolant isn't staying in the radiator long enough to cool it. I bet the bottom portion of the radiator is clogged. At slower speeds, the coolant stays in there longer and will cool better.

 

Thank You, LXMAN1. I will post results when the new radiator is installed. It is somewhere between Chicago and ?. I just know its not here, yet.

 

The engine is also producing a lot less power and HEAT at slower speeds! http://yarchive.net/car/engine_water_restrict.html

 

I received my new radiator and replaced it. The overheating problem is still evident, but not as bad. The next item to do is to clean the fins on the a/c condenser that fits in front of the radiator. The fins were in good shape but there was a lot of bug guts and small rocks(lots of gravel roads) jammed in between the fins. Does anybody have experience with removing the a/c condenser and seeing a difference in engine temperature?