The Stovebolt Site Forums The Shop Area Engine Shop thermostat

I can't figure out why my 216 will idle for 10 minutes with the temperature staying fine and then when I take it out and start running the truck down the road it starts to overheat. I pull it off the road and let it sit with the idea that I'm going to limp it back home and when I start back, the temperature is fine. This scenario has happened twice in a row. I have a new thermostat but I must be having some kind of air lock in the system. Does anyone have an idea what might be happening?

scottbit,

The problem 99% of the time is a old, plugged radiator.

A thermostat can stick, but this isn't normal. If you truck does this every time, that means the thermostat would have to malfunction the same way every time too...not likely.

You installed a new thermostat...why! Was the truck doing the same thing with the old one?

The gauge is showing hot...is the engine actually hot. You can smell/feel a hot engine.

A thermometer in the fill spout would confirm the accuracy of the dash gauge.

Did something happen to the truck before this happened. Did you tune it up and time the engine.

The plugged cooling system system would not allow the engine to cool down and run normally after sitting a spell, it would always cause the system to run hot.

I think the course of action would be to see if this actually a periodic heating, or is it really a constant problem while running the engine.

The thermostat has to be installed with the proper side to the block. If you want, you can remove the thermostat and see if this changes the chain of events.

Stuart

Take the thermostat out and place in a pan of boiling water it should open fully in less than a minute and close just as quickly when removed.

When the new stat was installed did you run the engine until it opened and recheck the coolant level.

Sometimes the coolant will drop due to an air pocket in the head finally filling. One way to reduce this problem is to loosen the sending unit to let some air out when filling the cooling system.

The radiator fan hasn't been off recently has it? If installed backward it will push air through the radiator from the engine side installed of pulling air from the grille side. It will cool well at idle but heat on the highway, the ram-air effect through the radiator is negated by the reverse air flow from the fan. I have seen this twice over the years with mechanical fans, first time my mistake, second time a customers vehicle. I have also seen this once with an electric fan, wired for a pusher when it should have been a puller.

John

I just made a little drawing, and it looks like the fan would blow exactly the same way if installed backwards.

Wouldn't the 'pitch' of the blades have to be reversed for it to blow backwards.


Stuart

The fan will pull the same direction if installed backwards but will not be as efective due to the curvature of the blades. There are fans made to go the opposite direction used with sepentine belts. Check the therm like Kip says or try another one. Iv,e had them defective when new & it will blow your mind.

One thing that hasn't been mentioned here is a collapsing rad hose and I think it could also cause this effect. Sometimes a rad hose will flatten with the higher engine speed and deny the engine the coolant flow rate that it needs.

Sure would like to know which of these, all good, suggestions it turns out to be