Just picked up a 2000 Sportage 4x4. On the drive home the sportage wouldn't come above C on the temp gauge. It was -10f on the drive home from where I picked it up. Today the temp is 1f and the same thing. I blocked off the radiator with a piece of cardboard and It does come up to temp. (around the middle of H and C on the dash. New Thermostat and the radiator is new as well. Any ideas?