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Here are the main problems that will cause overheating and how to detect the culprit. First, check your coolant level in your reservoir (removing the radiator cap while it is hot will only cause you to get seriously burned and possibly get into your eyes). If the reservoir is full, it will usually be the thermostat. It's only about $5 so fix that first. There is a way to test to see if it is bad by getting it cool then dipping it in hot water then cooling it off under cold water to see if it opens and shuts properly. In my opinion, not worth the hassle over a $5 part that should probably be replaced any time you service your coolant system anyway. If your reservoir is empty, then you need to check for the leak. The radiator hoses (especially old ones) can rupture and leak, causing coolant loss and overheating problems. The most obvious of all leaks would be if your car fills up with smoke that stinks like radiator fluid before you ever even exit the car.That would be the heater core. It doesn't take much of a leak to make it noticeable inside the car and will probably take quite a while with a slow leak within the heater core compartment to actually cause an overheating issue. That will need to be replaced asap or your windows will get a nice rainbow colored streak to them on the inside, the car will stink to high heaven, and it'll be a cold ride in the winter. If you're looking at the front of the engine and you notice a leak up front, check the water pump. When it fails, it will leak out the seep hole near the bottom of the pump. You won't be able to miss the puddle if you add coolant and it pours out the water pump the second you turn the car on. If you add coolant and it disappears immediately, but you see no leak, you better check the color of your exhaust. It'll probably be blowing whitish colored smoke. That whitish smoke is because the broken head gasket is allowing the coolant channels along the block to leak coolant into the oil. That means your head gasket is blown and will need to be replaced. It will have to be fixed immediately because it will overheat very quickly when you restart your engine. Another culprit is a little tougher to catch. You'll start your vehicle and everything will seem fine like the coolant is staying in the radiator. Then you drive to where you're going and look again and the coolant is all gone. In fact, you may not even overheat. You may, may not. (personal experience, mine never actually overheated) You don't notice any obvious leaks right away. Here's what's happening. While you're driving down the road, the coolant is spraying out the back of the engine. It's spraying out because your intake gasket is shot. Quite common in mid 90's GM vehicles anywhere from 60-120,000 miles. (including my own Yukon). That should cover most of the overheating/coolant problems that I can think of.

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