How to Properly Diagnose a Bad Head Gasket

Even if you aren't a professional mechanic there are steps that you can take to diagnose a bad head gasket. With only a few simple tools and a keen eye you can quickly determine if your head gasket is the source of your overheating problems, and save yourself an expensive diagnostic charge. Here's what you need to know to successfully test and inspect the head gasket on your vehicle.

Things You'll Need

• Inspection Mirror
• Flashlight
• Block Tester

Instructions

1. Look at the oil and examine in order to determine if engine coolant is present. When your head gasket fails it's often between a water jacket and an oil galley hole. A failure in this spot will allow coolant to enter and contaminate the oiling system. If you have coolant in your oil it will often have a creamy appearance to it, almost like chocolate milk. Even if the oil looks good on your dipstick you can drain out a small sample from the oil pan and examine it under light for the presence of water droplets.

2. Check the tail pipe to see if the exhaust smoke is white. Sometimes a bad head gasket will leak coolant into one of the combustion chambers causing a whitish, thick smoke to come out of the tailpipe. This can be hard to differentiate if the outside temperature is cold, but in warmer weather the excessive white smoke will be quite obvious.

3. Rev the car slightly while it is in park or neutral and pay attention to see if the engine wants to stall as the engine speed falls back to idle. A car with a failing head gasket will often have trouble maintaining a proper amount of engine vacuum and compression in the cylinders which will cause the engine to stall as it slows down. Be sure that your foot is on the main brake and that the emergency brake is also applied to prevent the car from moving forward while you are performing this test.

4. Inspect the surface where the cylinder head meets the engine block and look for coolant leaks. Many times coolant will seep out of the head gasket and run down the engine block. This can occur in a location that is hard to see, so you may need a flashlight and an inspection mirror. If you see coolant leaking anywhere from the gasket sealing junction, this is a definite indicator that your head gasket is bad.

5. Use a block tester to check for the presence of exhaust gas in the engine coolant. This is a tool that looks like a turkey baster and uses special dye that reacts with carbon dioxide to alert you to the presence of exhaust hydrocarbons in your antifreeze. You can purchase this tool at most auto parts stores for less than twenty dollars with the testing fluid included. While each kit will come with its own specific instructions, the general procedure is to fill the tester with fluid and carefully remove the radiator cap or the coolant reservoir cap. Then while the car is slightly warm you squeeze the bulb to suck in the fumes that float above the coolant into the tester. If there is exhaust gas in your coolant it will react with the fluid and turn it a different color letting you know that your head gasket has a leak between the combustion chamber and a water jacket.