If your cooling fan clutch is working right, the fan will spin up for a while, then spin down as the air from the radiator cools. With the fan engaged & spinning, you'll get cooler coolant for a little bit.

Good thought. I had the hood open and the fan was constant the whole time. If it were the fan, that could explain the engine heating/cooling, but the temp gauge and oil pressure were pulsing in unison, moving the same direction and the same amount as it pulsed. ??