I have a 89 si with a b20b, Its got a full race radiator, slim fan wired up to a switch, Motor has new water pump. The car only blows luke warm air out of the vents untill I start moving , then it starts to blow hot, Temp needle never goes hot or any where near, car always runs cool....any ideas? sound like a heater core? thermostat?

 

when I say the car runs cool I meen it runs at normal temp. sometimes it does drop down a little bit though

 

anyone?

 

....

 

You actually have two problems
"car always runs cool" is not good. Unless you have your ECU magically tuned not to watch temp then running cool isn't a good thing. You want the engine to warm up.

This is probably your problem
"slim fan wired up to a switch"

Hook your fan up to the ECT and let it do it's job.