When the temperature climbs
If the gauge moves into the red, a temperature warning appears, or you see steam from under the hood, signal and pull over somewhere safe. Switch the engine off. Turning the cabin heater to full hot can shed a little heat while you find a place to stop, but it is not a fix.
Do not open the radiator or coolant cap while the engine is hot—scalding coolant can erupt under pressure. Wait until the engine is fully cool, typically at least 30 minutes, before checking anything.
Common causes
Overheating usually comes from low coolant (often a leak), a stuck thermostat, a failed water pump, a blocked radiator, or a cooling fan that does not switch on. Hoses, the radiator cap and the expansion tank are also common failure points.
A one-time overheat in extreme heat or heavy traffic may have a simple cause, but repeated overheating points to a fault that needs proper diagnosis. White exhaust smoke or milky oil can indicate a head-gasket problem—stop driving and get a professional assessment.
After it cools
Once fully cool, you can check the coolant level in the translucent expansion tank against its marks and look for visible leaks under the car. Topping up with the correct coolant type may get you to a workshop, but driving any distance while overheating risks warped cylinder heads and engine failure.
If the level is very low, you see a major leak, or the gauge climbs again quickly, arrange a tow rather than risking the engine. Tow2 can help you find nearby towing and describe the symptoms for the workshop.