Constantly Running Radiator Fan

[sm12511]

Hi guys, I'm a noob, so if someone's already covered this, I accept all redirects.

Anyway, got a 1995 ES300 with over 200k on the clock. Just recently after replacing the power steering pump by myself (what a pain that was!), the fan for the radiator blows constantly, even when the car is cold. The fan, I know, is hydraulically controlled, so what could this be? The car doesn't overheat, I just put in a brand new thermostat and coolant temp sensor, and the dang thing still is going full blast! In fact, the car never really heats up because the fan is going all the time. What gives? My son's insisting that I put yet ANOTHER thermostat in, but as we all know, that thing is tucked up under there pretty good, and I don't really want to if I don't have to. Someone please help!

[sm12511]

Maybe, could it be that darn solenoid on the bottom of the ps pump? I had to use the one off the old pump, and that's all I can think of. But something tells me those things are going to be expensive. Any yeas or nays?