What to do immediately
Turn off the A/C and turn the heater on full — this pulls heat from the engine. If the gauge keeps climbing, pull over safely and shut off the engine.
Never open the radiator cap on a hot engine. Pressurized coolant can cause severe burns.
Common causes
Low coolant from a leak, a failed thermostat, a bad water pump, a clogged radiator, or a broken cooling fan. In older vehicles, a failing head gasket can also cause overheating.
Why you shouldn't keep driving
Driving an overheating engine can warp the cylinder head and blow the head gasket — turning a $300 repair into a $3,000 one. Tow or call for help.
How to prevent it
Flush coolant every 60,000 miles, inspect hoses and the radiator cap, and watch the temperature gauge — especially in summer traffic.