my 92 prelude s radiator fan wont turn on when it gets up 2 temp? but will turn on when i shut the car off? anyone have any ideas?

 

fan switch seems a likely candidate; it's part of the t-stat housing.

 

There are two fans. One uses the coolant temperature and has a relay in the fuse box. The other runs when the airconditioner compressor is on.

The relay is controlled by the ECU and goes on when the Coolant temp > 190 or so. The ECT (Engine Coolant Temp ) sensor has one red wire on it. You can remove the wire and measure resistant between the center pin and the engine. You should have 32-49 ohms when the engine is running at the right temperature. The higher the ohms, the colder the reading. The fan will likely come on around 38-40 ohms.

A likely problem is a bad ECT sensor. The engine temp tends to climb when you shut the engine off. If you want to test if, you can put a 30 ohm resistor from the red wire to ground and the ECT will think the engine is hot. The fan should come on pretty quickly.