Check the antifreeze (coolant). The engine cooling system should be filled with a 50/50 mixture of antifreeze and distilled water to prevent freezing and boiling over. Antifreeze testers are available at your local auto parts store to test the mixture. To keep the cooling system operating at peak performance, follow the manufacturer’s recommendations for changing the antifreeze (flush and fill). In addition to changing the antifreeze, pressure testing the cooling system on an older vehicle may expose a minor leak before it becomes a major problem. Most repair shops charge a minimal fee for pressure testing, and some shops will do it for free.