In hindsight, my car was doing the same thing ....until the thermostat broke...in the closed position and I overheated.

The car always seemed to run cool, and in my short commute to work, would not always reach operating temp.

Easy and cheap to replace but oh so vital to the well being of your car.

Change it out and look at the bridge of the thermostat. That is where mine broke in two.

glenmore
1991 300CE