I spent pretty much the whole day fixing a few bugs on the engine, the engine runs great, but I cant figre out why my fan wont turn on, so far I have:

Jumped the fan relay to make sure it works, it does.

Used a different relay, I used the one out of my sedan and I know that one works.

Switched the 2 wire sensor on the water neck again from the sedan.

The only thing I did not change (and I have a feeling this is it) is the 1 wire sensor that goes in to the head, is this the sensor that activates your fan? or the one that displays your temperature on you cluster?

If any of you know what else would cause your fan to not run, please let me know.

 

if your fan runs when you jump the relay terminals, then it's probably a problem with the coolant tempurature sensor. Get a multimeter out and check how much resistance your sensor has. Not sure exactly what the spec will be, but if you get a really high number or OL reading on your multimeter, I'd bet that you need a new sensor. Also may be a wiring issue, but I'd say that's unlikely.

 

This may not be as likely, but you can also check that the coolant is flowing properly. If for some reason the sensor isn't in contact with the hot coolant (i.e. air in system, poor circulation) it won't switch the fan properly.

 

Had the same problem, checked all the wiring and relays and everything was fine. Ended up being the "fan switch" that screws right into the block, a $20 part you can get at any autozone or advanced auto parts. I ended up checking everywhere for it, but instead of it being called a coolant temperature switch or sensor, it was just called a fan switch. Hope that helps, if fan works, wiring and relays check out, it is most likely your problem. Good luck