by Jim Miller

The engine is consuming too much oil. There may be smoke from the tailpipe.

There are many items that can cause the engine to consume too much oil. If there are leaks present, address that symptom first. The engines oiling system provides lubrication to critical moving parts within the engine. Some of theses parts, such as the rings and valve guides, require lubrication and keep the oil from entering the combustion chamber. If these parts wear, too much clearance between the mating surfaces will exist and will allow the oil to enter the combustion chamber where it will be burnt and exhausted out of the tail pipe. Over time the engine oil will become low. Engines will burn a certain amount of oil. If you change your engines oil every 3,000 miles, running a 1/2 quart low on oil at the time of oil change can be normal. The most usual cause of engine oil consumption is worn valve guides, usually the exhaust guides or worn piston rings.

Run the engine for several minutes at idle. Turn the engine off and let it sit for about 15 minutes. Restart the engine and immediately increase the engine speed while observing the exhaust. If a heavy billow of bluish smoke is exhausted then disappears and the exhaust remains relatively clean, the most likely cause is excessive valve guide wear. In this case, the valve guides or valve guide seals require service. If the above test only produces mild smoke and the smoke remains at the same level during all operating conditions, the piston rings will have to be tested. This is done by performing a compression test on the engine. The first test is referred to as a “dry test” and the second test is referred to as a “wet test”. The dry test consists of measuring the engines compression using a compression tester installed in the spark plug hole and the ignition system disabled. The engine is then cranked and the pressure is measured and recorded. A few teaspoons full of oil is then poured into the spark plug hole and the compression is then measured again. If the reading increases more than 15 PSI, the rings are worn and major engine service is probably required.

Use caution when working around hot or rotating engine parts. Compression testers are available at most auto parts stores. Refer to the manufacturer’s instructions for proper useage. When performing a compression test it is critical that the ignition system be disabled to prevent the engine from starting. This is usually done by connecting a wire to each of the spark plug wires to a good engine ground away from your work area. Refer to a manufacturers specific service manual for proper testing procedures.