Bought a 1994 Hatch a week ago for a project and heres a small break down…
Complete B18C1 swap engine and trans, drove home fine noticed temp sensor not working so here it goes,I’ve replaced everything, new temp sensor, new temp sender, new temp switch, new thermostat, car has a new radiator, but the car still over heats and fans will not cut on…
I've done everything every other forum has said, ive bled the coolant system, ive jumped the switch and yes the fans DO come on, I’ve replaced every sensor and switch but it still over heats, at this point im going in circles looking over everything and just can not figure it out, please help, thanks.

 

What brand of thermostat did you use ? If you can jump the fan switch plug and the fan comes on, then you either have a bad fan switch or a bad thermostat. If these two items are functioning properly... you have a head gasket issue and this is why you are overheating. have you tested the cooling system to see if there is evidence of exhaust gas in the fluid ?

 

I believe it was a Motorad thermostat 170° F, havent checked for gasses in the coolant system, but for the main part i didnt see any bubbles (i know not fully relevant) or any coolant loss (which also isnt fully relevant to minor head gasket problems) i cant say the car “fully” over heats, never touches the red line just sits about 3/4 of the way or right on top of the little symbol , and i replaced the switch and the fans still wouldnt come on unless forced on with a jumper

 

In order to close the fan switch and turn on the cooling fan, fluid on the front side of the thermostat must reach the proper temperature to do so. If the small bleeder hole at the 12 O'clock position is too small OR too large... or the bypass circuit isn't functioning/flowing properly, coolant will not reach the proper temp on the front of the thermostat. It is my experience that only GENUINE Honda thermostats work properly and attempting to use other brand thermostats only prolongs solving your overheating issue.