I own a 2012 Volvo T5 S60. It’s a good car, with 135,000 kilometres. This summer, I noticed the oil levels on the dipstick registered empty. Since then, I’ve had to refill/top up oil to keep the levels up. The oil appears dark brown and smells slightly burnt. Still, the car doesn’t smoke when I start it, no leaking below and no warning lights about low engine oil levels.
My mechanic is going to check the PCV valve soon, but warned he thinks this might be something else. Do you have any suggestions?
Thanks – Denis A.
While checking the positive crankcase ventilation system (PCV) is a necessary step in any oil consumption diagnosis procedure, I doubt in your case that it will yield a fix. I say this because there is a known problem within your engine that is likely the culprit. Here is what I believe you are dealing with.
Almost every modern engine, regardless of manufacturer, uses pistons that have three ring lands that encircle the piston that the piston rings sit within. While the top and middle rings are single rings, the bottom oil control ring is an assembly using a three-piece-ring setup. The only job of this bottom ring assembly is to scrape oil off the cylinder walls; oil that is squirted onto the wall as part of the internal lubrication process. The majority of oil is supposed to drop back into the engine oil pan during this process.
Historically, piston rings were hefty with plenty of tension that did the job very well. Then, along came fuel conservation initiatives and, in an attempt to increase an engine’s fuel efficiency, carmakers were forced to scrutinize every part of the combustion process. Consequently, over the past several decades these heavy-duty rings which had significant drag have been replaced with low-friction piston rings that are as close to drag free as they can possibly make them.
Low-friction piston rings increase fuel efficiency but can also be problematic especially in older vehicles. Piston rings are meant to be free floating, rotating freely within their lands so that wear is distributed evenly. The reality is that these lighter, flimsier three-piece oil control rings become easily infused with carbon and seize in one position. A seized ring will wear unevenly and stop performing its job effectively. Engine oil will now slip by all the rings and end up in the combustion chamber where it will be burned and sent out the exhaust.
Detected early enough, a service called an oil flush can help a bit but rarely outright fixes the problem – it merely slows the oil consumption. The ultimate repair is to replace all the engine’s pistons and rings, which is a costly procedure probably exceeding the value of your car. Your technician will likely recommend an oil flush at some point soon just to see if it will help. It may but most likely you will be faced with a large decision to either keep the car and spend significant dollars or to get rid of it.
Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.
Shopping for a new car? Check out the new Globe Drive Build and Price Tool to see the latest discounts, rebates and rates on new cars, trucks and SUVs. Click here to get your price.