06 ranger thermostat trouble

I just bought a used 06 ranger sport. It runs fine, but during the first 5 minutes of driving the thermostat will act funny. It can shoot from cold to very hot within 30 seconds. It will stay there for a minute or two, then within seconds it will drop to normal. It may go up again, but after a few minutes it does not go up again. Has anyone ever run into this?

Don’t Guess. Get The Truck Checked Immediately. It Could Be A Faulty Sender Or Gauge, But Sounds More Like Air In The Cooling System And You’ll Damage Your Engine.


With The Vehicle Cold, Has Anyone checked the coolant level in the coolant reservoir and radiator (if it has a cap) ?

The radiator should be full and the reservoir shouldn’t be empty.