Here is the situation: I recently changed my radiator, bleed the system (NO air), ran and topped-off, everything was OK. Temp gage sits at 1/2 way--perfect.

Yesterday, after my 50mile drive home, I parked letting the engine idle and did a visual inspection. I noticed that my over-flow tank was nearly empty and my fan was NOT on.

I then turned off the engine and my over-flow tank filled back up with boiling fluid?

What is the problem? Is my thermostat not opening, do I have a bad relay?

I know how to check if the fan is dead, by using a 12V source, which I will do today while there is still light, but if the fan works--what else could it be?

I am ruling out the HG, because I have NO water/coolant in my oil, and I am not blowing any smoke out the tail.

Any insight would help--Thanks.

 

When my cooling fan stopped working it was the connection to the coolant temperature sensor. One of the wires going to the sensor itself was not connected (by that I mean it was "cut") I just spliced them back together and all was good. You could check check to make sure you're getting voltage to that as well.

 

Are you sure the system is full of coolant?

 

to check your fan,

take out the connector to the thermostat sensor and stick a paper clip in three to jump it to itself.
the fan should turn on immediatley.

also chekc your radiator cap.
i had a similiar problem and turned out to be that.