One of the easiest types of preventive maintenance for your cooling system is to make sure to replace your radiator cap and thermostat every 20,000 miles or every couple of years if not driven that much. Thermostats stay in a closed position, allowing very little waterflow through until the engine heats up to a certain temperature. If the thermostat gets sticky, then it might not fully open up which in turn will not allow enough coolant to run through the system. The radiator cap usually holds either 13 or 16 pounds of pressure within your cooling system. If the cap is old or faulty, proper pressure will not be held and your cooling system could boil and overflow, emptying your cooling system of its vitals.