Many owners of Suburban’s, Avalanches, Silverado’s, and Tahoe’s are claiming they need a new quart of oil every 1000-1500 miles without any visible leaks. This particular 2005 Chevy Tahoe had come in describing a much more severe situation. The customer had a complaint of losing approximately 1-2 quarts every 750 miles or so. Multiple tests were performed including a compression test which found little to no compression in one of the cylinders. A follow up leak down test had found that the cylinder was losing the compression both back through the intake via worn valves and pitted valve seats as well as into the crankcase through the piston rings. Cylinder head removal and engine oil pan removal was required to pull the piston from the suspect cylinder. The defective parts were verified by a visual inspection. The technician had found the oil control rings were “gummed up” and stuck inside of the piston ring grooves allowing by pass. The attached pictures show the story. The remedy in this particular case ended up being a complete engine replacement due to the high mileage currently on the truck.
About Oil Consumption —– All engines require oil to lubricate and protect the moving parts of an engine from wear. These parts include cylinder walls, pistons and piston rings. When a piston moves down its cylinder, it leaves a thin film of oil on the cylinder wall. This tiny amount of oil partially gets consumed by the combustion process and therefore it’s normal to see a small amount of oil reduction is the engine. What’s not normal, however, is to see the rapid and extreme oil consumption of some Chevrolet engines.
What Causes Chevrolet’s Oil Problem? According to a Chevrolet service bulletin, the most common cause is stuck oil control rings. Generally the stuck oil control rings are the result of excessive oil on the cylinder walls and this excessive oil can come from the PCV system and/or the AFM pressure relief valve in the oil pan. Upon inspection of an engine experiencing this problem, you will typically see an oil-fouled spark plug. Although excessive oil may also show up in the intake manifold.
If you are currently experiencing excessive oil consumption be sure to have your vehicle diagnosed by a certified automotive professional.