Overheating Diagnosis at Johnny's Automotive

The moment the needle heads for the red, get off the road and shut it off. Heat damage happens quickly, and the difference between a cooling system repair and an engine repair is often the few miles somebody drove after the gauge went up. Pull over somewhere safe, turn the key off, and pull the hood latch so heat can escape.

Don't open the radiator cap or the coolant reservoir while it's hot. That system is under pressure, and opening it hot sprays scalding coolant. Everything needs to be cool enough to touch first, and that takes longer than it feels like it should.

Then have it towed. Limping it in feels like the cheaper choice and it usually isn't. A car that overheated once and was shut off is normally a cooling system conversation. A car driven until it stopped is a different one.

Once it's here, the order is the same every time. Pressure test the system to see whether it holds and where coolant is escaping. Check the cap, because a cap that won't hold its rated pressure drops the boiling point all by itself. Confirm the thermostat opens at the right temperature instead of assuming it's stuck. Watch the fans actually come on at the trigger point, and check that air can get through the radiator at all. If the system holds pressure and still runs hot, a combustion gas test looks for exhaust gases in the coolant, and that answer moves the conversation to head gasket work.

Guessing here is expensive, because coolant looks the same no matter why it's leaving. Testing is what tells you which part is at fault, and you get that answer with a written quote before anything gets replaced.