In addition to changing the oil, there's another part of keeping the engine cool that you can't overlook -- the cooling system itself. The cooling system includes the radiator, thermostat, water pump and coolant. The easiest way to protect your engine from overheating is by making sure you have the proper amount of coolant (radiator fluid) circulating throughout your engine.
The coolant circulates through your engine when the thermostat determines that the engine is getting hot and needs to be cooled down. The water pump then pulls coolant from the radiator, sends it into the engine block and then back out to the radiator to be cooled back down. To check the coolant level, lift the hood and look at your coolant tank. It's a clear tank with a green or orange colored liquid in it. Make sure the coolant is above the minimum mark but below the maximum mark.
If you notice that your car is overheating and you know that there's enough coolant, take your car to a mechanic and have them run a cooling system check. The cost to find and replace a problem with the cooling system ahead of time will far outweigh the damage done to your engine if it ever overheats.