An engine that burns oil not only wastes oil but can damage spark plugs, cause the ignition to misfire and eventually affect the catalytic converter. The burning oil can also cause higher emissions, resulting in failed emissions tests due to excess hydrocarbon production
REASONS FOR ENGINE OIL BURNS
1.Worn Valve Guides
Over time, the valves wear down the cylindrical chambers, or valve guides, that keep them on track and create a gap in the chambers, this gap allows oil to flow into the combustion chamber, where it then burns. Once the gap becomes too big, the valve seal cannot prevent the oil from making it into the combustion chamber.
2.Bad Valve Seals
The valve seals prevent the flow of oil into the engine. If the valve seals fail or are broken, cracked, worn down or improperly installed, the oil will be sucked into the engine and cylinders,the compression may not be affected by the leaking oil but the engine will use a lot more oil than necessary.
3.Pressurized Oil Pan
If carbon, a byproduct of the engine, builds up in the positive crankcase ventilation (PCV) system, it can clog the system. Generally, the PCV system acts as an exhaust or breathing passage for the engine, but build-up pressurizes the oil pan. This pressure pushes oil into the engine through the fuel delivery system, and the oil burns.
4.Worn Piston Rings
If the piston rings that seal the engine's combustion chamber wear out, the pressure is sent back down to the oil pan, creating the same end result as when carbon builds up in the PCV system.If the rings are installed upside down, twisted onto the pistons or not staggered correctly, the result will be the same as if they had worn out.
Diagnosing the problem
-Check the oil. Open your car's hood and pull out the oil dipstick. Wipe the dipstick clean with a clean rag and insert it back into its tube. Pull the dipstick back out and check the level of the oil. Add oil until the dipstick reads full. Repeat this every 500 miles. If it reads a quart low in 500 miles, you have an oil burning problem.
-Check the exhaust. Blue smoke coming from a car's exhaust pipe while it is running is a sign of oil burning. Smell the exhaust. An engine that is burning oil produces higher emissions. It will also fail to pass an emissions test due to elevated hydrocarbon emission.
-Monitor the engine to see if it is misfiring or running rough. An engine that is burning oil will foul the spark plugs, causing it to run rough.
-Inspect the spark plugs. Pull the spark plug wires off one spark plug. Use a spark plug wrench to remove the spark plug. Examine the spark plug. An oily, wet or sooty spark plug terminal is a sign of oil burning. Replace the spark plug and wire. Repeat for each spark plug, working on one spark plug at a time.
DIAGNOSING INDIVIDUAL CAUSES
Remove the PCV valve with the engine running. There should be a strong vacuum pulling on the valve. If there is no vacuum, the system is clogged with sludge and carbon. It should be cleaned and the valve replaced.
Valve guides and valve seals
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.
Worn out Piston rings
remove the spark plugs and test each cylinder individually for the total PSI of compression. If you find that one cylinder is low, then wet test it. To wet test the cylinder, remove the gauge, squirt oil into the cylinder, and then retest it. If the compression in that cylinder comes up, then that cylinder has worn piston rings. How do we know this? Because when oil was squirted into the cylinder, it filled the gap between the worn rings and cylinder wall, sealing the ring gap and thus increasing compression. In this is the case, consider rebuilding or replacing the engine.
NOTE:Compression testers are available at most auto parts stores. Refer to the manufacturer’s instructions for proper usage. 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
Hope this helps you .Cheers!