Ok i have a 91 si hatch with a B18b in it and i noticed today when i went for a short drive toa friends house the motor was chilled temp when i left cause its been sitting all day in my shaded garage, well the travel to my friends house was about 5 minutes 10 at the tops. I got over there and i popped the hood to show them my new valve cover and the motor was extremly hot.
So i fired the car up and left it run idle for few minutes, the Temp gauge stood right in the middle where it was supposed to be but what we did notice is the radiator fan did not come on at all... My dad told me the fan should have came on at the turn of the key before even firing the motor up beings the motor was that hot....

So i waited awhile till it cooled down then made the travel back home and again i checked to see if the fan came on from the trip home and it didnt so me and my dad checked to see if maybe the fan harness got disconnected and that checked out fine and we checked the fuse(s) and those checked out fine...

I told my dad what we'll end up prolly having to do is, Running a toggle switch on the dash and running the rad fan 24/7... But he told me to post this on here and see what i come up with so Please help us fix this problem!!!!!

 

It might be the sensor on the back of the block it called the temperature sending unit. It has a little harness going to it. The sensor has two little prongs sticking out from it. Check your fan first before you going buying anything though. Run a from the fan directly to the battery to see if the fan comes on first. It could be a bad relay which is located on the front passenger side near the corner lamps. I have my fan hooked up to a toggle switch though. So good luck.

 

Check the coolant temp switch on your motor, chances are you forgot to wire it up when the swap was done. Your stock motor has the temp switch on the back near the oil filter as a prong male plug but the newer B18B has it as a normal 2 prong sensor on the thermostat. All you need to do is extend the wires in the harness up to the thermostat and change to a 2 prong plug and you're done.