hi all. i recently bought a 1991 dodge shadow. the first things ive done to it are to change the oil and oil-filter, and to drain/refill the radiator. since ive done this my temparature gauge now fluctuates up and down between the 2 middle lines of acceptable tempuratures. it happens when i have the car in Park. The temperature needle starts to go up, till it hits the line, then I hear the fan turn on to cool the engine, and the needle falls back down to the cool line. isnt the needle supposed to stay constant?

when i drive the car, after a mile or so the needle falls to where its supposed to be and stays there, it only fluctuates when i have the car in Park mode.

any ideas?

 

Sounds like a clogged radiator or bad water pump.