Engine coolant does more than protect your engine from freezing and cracking. Coolant also contains anti-corrosive additives and water pump lubricants to keep your entire cooling system in tip-top shape. Test the level of your coolant's freeze protection using an inexpensive tester. Suck in some coolant from the coolant reservoir and read the results on the scale printed on the tester. But don't stop there. Just because coolant tests ok on the freeze protection doesn't mean the additives are in good shape. To check that, you'll need a digital multimeter. Begin with a cold engine. Remove the radiator cap and start the engine. Set your digital multimeter to DC volts at 20 volts or less. When the engine reaches operating temperature, insert the positive probe directly into the coolant. Rev the engine to 2,000 rpm and place the negative probe on the negative battery terminal. If the digital meter reads .4 volts or less, your coolant is in good condition. If it's greater than .4 volts, the additives are exhausted, and you may be in the market for a new radiator, a water pump or a heater core in the future. All of those are far more expensive than a simple coolant change. Learn more about how to test coolant here.