Watch the Temperature Gauge
Nothing ruins a car faster than overheating. Just because you're nice and cool in the passenger compartment doesn't mean that your engine isn't dying of heat.
If you do notice your temperature indicator starting to rise, turn on the heat in your car. Your car's heater core will divert a little more of that heat away from the engine (remember--the heater core is another little radiator). Sure, the passenger compartment will get hot--maybe unbearable--but you might save the engine. Overheating can ruin an engine. So, if the temperature gauge is running hotter than it normally does, take these precautions, slow down and get some help at the next opportunity. If the engine is actually overheating—that is, the needle is near or in the red zone, or the “hot” light is on--stop driving. It may seem inconvenient, but you will almost certainly ruin the engine if you drive while it's overheated.
You should have your Air Conditioning system checked also.
Things to Bring on Your Summer Road Trip.