[lazydawg]

Just broke in new engine today but the elec fan would not come on so we jumpered the relay and continued the break in.
After a little trouble shooting it looks like it is the thermo sensor, but I have no idea how to check it. Does a single wire sensor internally ground when it reaches "on" temp to complete a circuit to ground for the relay? Suggestions please!

 

[S10 Racer]

Just broke in new engine today but the elec fan would not come on so we jumpered the relay and continued the break in.
After a little trouble shooting it looks like it is the thermo sensor, but I have no idea how to check it. Does a single wire sensor internally ground when it reaches "on" temp to complete a circuit to ground for the relay? Suggestions please!

A one wore switch operates like you think, completing the ground when it reaches the switch setting. Is the switch an original equipment or did you just buy one and install? The reason I ask is that I did the same thing with a 327 in an S10 and found out that the switch they sold me was for a computer system and not a mechanical. It would not allow it to complete a ground no matter how hot it got. I replaced it with an older model switch and it worked fine. Just a thought.

 

[lazydawg]

Bought it fm Summitt for generic use. Used in SBC with Cooling Components CCI1770 fan and AAW 70 amp wiring harness and relay.
Summitt did call me about the part they sold and asked me to read the printed numbers on it as some were part of a recall of some type, but allegedly this was not one of them. BUT it sure makes me question it!!

 

[XNTRCI-T]

You probably already know this, but just in case... did you use thread sealant on the switch? If so, it may be preventing the completion of the circuit.

 

[lazydawg]

No did not have sealent (teflon tape) as I think they said not to use it. Unfortunately it was weeping while running and no matter what tightening was done the leak continued. So I put on some teflon paste and at least the leak stopped.
I did figure out that I could test the sensor with an ohm meter and heating it up with a heat gun, only problem was I could not determine what the opening and closing temps were. Sure hope the paste only fills in microscopic areas and that some where the threads touch the block