The short answer: Pull over as soon as it's safe to do so, turn the engine off, and do not open the radiator cap while it's hot. Continuing to drive — even "just a bit further" to reach home or a workshop — risks warping the cylinder head or blowing a head gasket, turning a coolant top-up into an engine rebuild.
The moment you notice the temperature gauge climbing toward the red, or a warning light appears, indicate and move to the shoulder or a safe side street as soon as you reasonably can — don't wait for a "better spot" further down the road. Turn the engine off completely rather than idling, since idling still generates heat without the airflow a moving car gets.
One temporary trick while you're still moving toward a safe stopping point: turn the air conditioning off and the heater on full, with the fan on high. It sounds counterintuitive, but the heater core pulls heat away from the engine and out into the cabin, buying you a small amount of extra cooling margin for the seconds it takes to find somewhere safe to stop.
Never do this: Don't open the radiator cap or coolant reservoir while the engine is hot — pressurised, near-boiling coolant can spray out and cause serious burns. Wait at least 20–30 minutes after stopping before checking any fluid levels.
Once stopped and cooled, check the coolant level if you can do so safely, but don't top it up and continue driving as if nothing happened — overheating almost always has a cause (a leak, a failed thermostat, a broken water pump, or a blown hose), and that cause needs diagnosing before it happens again. Call for a tow or roadside assist rather than risk driving further on a car that's already overheated once.
Car Overheated Recently?
We'll find out why before you're back on the road, not after it happens again.