Well i just purchased a 88 Si but with the D15 in it today. The temp. guage isn't working properly though. When i start it up it says cold but like 5 seconds later it rapidly goes up to Hot and stays there until the car is shut off.

The fan is turning on so it isn't that. What else could it be? Thanks in advance.

 

Sounds like there's a wiring problem. Try to trace what has been changed in the swap, and see what doesn't add up. It sounds like the gauge is getting straight power from sensor power from the ecu or something.

 

Well my first guess is the coolant temp sensor. Just because the fan turns on and everything and it turns on REAL fast, like within 5 minutes or less of driving it. So i'm going to see if that's the problem if not then i'll double check all the wiring. I didn't do the swap btw. It was the guy before me.