Why is my car overheating

External coolant leak, a pressure should show that one. Blown headgasket or a cracked cylinder head, you can purchase a DIY kit from your local parts store for testing, or have your favorite independent shop do the test for you.

The most common reason for coolant vanishing is a broken water pump or a leaking radiator hose. I'm guessing the car is overheating too. Just look under the car to see the puddle. Coolant leaks are usually just minor repair items on older cars and everyone has to deal with them occasionally.

If coolant is found on the ground, you simply have an external leak. If coolant is simply vanishing leaving a low or empty radiator, I’m afraid you have an internal leak which is costly and will quickly lead to a much further broken engine if you keep driving it. There are some over the counter stop leak liquids you can try (go to your local car parts place and ask) but these usually only solve the leak short term and make the vehicle untrustworthy. External leaks can still be costly, but if you don’t drive with out coolant, your engine should be okay. If you drive with it dry, you’ll murder the engine in an eye wink. Use regular tap water to refill until you get it fixed and be careful to not overheat the engine if possible