What to do if your Engine Overheats - 4
If the steps listed so far didn't help, you should have the car towed to a competent garage right away. Do NOT drive with your temperature needle in the red as it will destroy your engine.
If the mechanic nails it down to a faulty thermostat that refuses to open, ask him to remove it as a temporary quick fix. This will keep your car running cooler than normal, yet that's better than excessive heat.
Other overheating causes are a faulty pressure cap (unlikely if you are using OEM parts), a snapped fan belt (older cars only), blown head gasket, water pump failure, incorrect engine timing or a sensor gone bad.
Once you are back home:
The above-mentioned remedies are listed only to get you out of a sticky situation. Remember to have your car completely checked at a competent garage at the earliest opportunity. Also, using 100% water in the radiator was meant to be a stopgap measure. You should flush out your radiator and fill it up with a manufacturer-recommended ratio of coolant : water.
Lastly, remember to flush your radiator every two years.