2. “Pushing coolant”, or coolant in the cylinders If a break occurs in the head gasket between a cylinder sealing ring and a water passage, a couple of things can happen. Depending on the temperature and pressure in the coolant system, coolant can be drawn into the combustion chamber and burned, or pressure from the cylinders can leak into the coolant system…or both. When coolant is drawn into the cylinders and burned, you will usually notice the distinctive “sweet” smell of burning anti-freeze from the exhaust, assuming you aren’t running pure water. You can also smell this under the hood sometimes, but check for a radiator or coolant hose leak before assuming you have a blown HG. There may also be white smoke coming from the exhaust. (FYI – burning coolant produces white smoke, a rich fuel mixture produces black smoke, and burning oil usually produces blue or bluish-white smoke). You’ll also more than likely feel a difference in the car’s power, although this can vary a great deal from hardly noticeable to extreme, again depending on the size of the leak. At the very least, you’ll likely notice a miss or strange idle; at the most you could theoretically hydro lock the motor due to fluid in the cylinders, although I’ve never actually heard of this happening. When it goes the other way and air escapes from the cylinders into the coolant, you’ll get the often-mentioned “pushing coolant” scenario. What happens is the compression in the combustion chamber pressurizes the coolant system, causing it to bubble or flow out of the radiator overflow bottle. This type of failure will usually cause the car to run hot, and can quickly cause a cascade of other problems. Although you can buy equipment to test for this, there is a cheaper method that has been used for years. Remove the thermostat (with the engine cold!), start the car, and observe the fluid flowing through the thermostat housing after the engine is warm. If you see it bubbling or the level bouncing around dramatically, you may have a pushing coolant issue. Note: A few occasional bubbles in the coolant means that there is air in the system, but not necessarily from a head gasket failure. If this is the case, the air should work it’s way out of the system within a few minutes. If you are pushing coolant, it won’t stop and the bubbling will probably be more dramatic.
Posted on: Tue, 02 Jul 2013 07:26:23 +0000
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