Originally Posted by RotorHead
Alright, I have an 88 S-10 with a 350. I am using a corvette radiator mounted where the A/C coils were. Installed is a stant 180 thermostat and a 185 on / 170 off thermal switch controlling a single 16" fan pulling. Granted it is in the 30s and 40s, but when I crank it up and watch the temp, I can watch in creep up to 185 and when the t-stat opens and the fan comes on the temp drops to 150-160. Now when I drive around, it drops to between 140-150 and won't warm up. Also, I am running an air gap intake and I do know that they are hard to warm up. I first thought it was the t-stat stuck open but I changed it, should I get a 190 t-stat or put a toggle switch in the relay circuit for the fan? I'm leaning on not going with a 190 because it is cold here and it will probably be a different machine in the summer time. Any suggestions would be greatly appreciated.
The temp shouldn't drop below the thermostat's opening temp, it's more common is to see the operating temp a little above that and pretty constant. You don't need to turn the fan on at the same temp the thermostat opens, keeping that about 10-15 degrees hotter before it switches on is sufficient, the fan is there to supply air across the core when the vehicle is not moving. Still the fan shouldn't pull the engine temp down so low because the thermostat should close and cut off circulation through the radiator.
What about the bypass circuit? That should originate on the engine side of the thermostat and loop, often through the heater core, back to the pump inlet. This connection is often at the pump with a fitting on top, it can also be back to the pump suction side radiator tank, or a tee into the suction side radiator to pump hose. The return should not go into the return side of the radiator or there will be a flow through the core when the engine is still cold. If there is a vent hole in the thermostat, it should not be more than 1/8th inch. Too large or too many will bypass too much coolant rendering the thermostat's attempts to hold a narrow range of temperature pointless.
You also need to be sure the pump is the correct rotation for the belt system. Getting this reversed leads to weird problems, among them the thermostat will be pressurized against its seating direction which can force it open before its ready to be open or hold it open when it should close.