I would first buy a Taylor cooking thermometer, 100 to 400 deg. range & when the motor is up to operating temp & while still running, CARFULLY remove the rad. cap & drop the thermometer in to 'calibrate' the reading on the truck temp. gauge. Using that as a starting point, I would try to not go much past 200 deg. with it due to possible hot (steam) spots in the motor.
Doug
