It may be hard to believe, but all internal combustion engines (ICE) consume a bit of oil during the combustion process. Whether you have a gas or diesel vehicle, the engine will burn oil, and it doesn't matter if it's a new car or old jalopy. The real trouble begins when the car consumes more oil than what the manufacturer deems acceptable. There are no government standards regarding oil consumption in ICE engines, so only the manufacturer can tell you if your car's engine is toast or within the prescribed limits.
So, how much is too much? If you find yourself refilling the engine with a quart of oil every 1,000 miles or so, it's probably time to visit your mechanic, especially if you notice dramatically low oil levels when checking the dipstick. Oil manufacturers claim passenger cars can burn 0.1 to 0.3 liters of oil for every 100 liters of fuel. But if your dipstick is suddenly showing low readings, your engine may have oil leaks from worn seals or gaskets, which can degrade and turn brittle over time. It could also mean your engine is losing oil while driving, and you'll need to refill it with oil more frequently to combat imminent damage.
If there are no visible leaks, the problem could be deeper, such as leaky head gaskets, damaged cylinder walls, worn-out valve seals, or degraded piston rings. Whatever the case, repairing those issues is sure to burn a hole in your pocket, so you'd better be wary if your engine has no leaks but keeps losing oil. On a brighter note, a clogged or malfunctioning PCV valve can also cause excess oil consumption, and it's worth checking before deciding on an expensive overhaul.
As if always buying a quart or two of oil for refilling is not enough of a burden, an engine that burns too much oil will inevitably develop other problems later on. Driving with an illuminated oil light is unsafe for the motor and could grenade the engine if the sump runs dry, which is why you should pull over and turn the engine off when the oil light turns on. Your engine doesn't have much time with dwindling oil reserves, and you're inflicting premature wear and tear each time it runs with insufficient oil.
Meanwhile, inadvertently burning oil with the air and fuel mixture produces soot and carbon deposits that gum up moving parts and choke the engine's performance. Motors that burn oil are also prone to the formation of sludge, a thick and gooey substance that necessitates a comprehensive (and expensive) overhaul if bad enough.
Furthermore, along with the increased carbon deposits are more harmful emissions, which can take no time in clogging your catalytic converters. If the sudden oil consumption comes with other symptoms, like excessive black or bluish smoke from the tailpipe, poor acceleration, and rough idling, you could be dealing with worn valve stem seals.
One reason why choosing the right oil is important is to prevent sudden oil consumption. Each engine requires a specific type and grade of motor oil, and using the wrong kind of oil can cause your engine to degrade from within. Of particular importance is the oil viscosity, as there can be severe consequences if you get it wrong.
Using lower viscosity oil may improve the flow on cold starts, but it could degrade or evaporate quickly, resulting in low oil levels, as well as fail to provide adequate lubrication for the internal parts. On the other hand, using thicker oil may induce more wear on cold starts. It can also cause the engine to work harder and increase engine temperatures, contributing to increased wear and tear.
Some cars have engines that are notorious for consuming oil, including models like the 2010 to 2015 Audi Q5, the 2012 to 2019 BMW M5, and the 2010 to 2013 Chevy Equinox/GMC Terrain. So, if you own one of these vehicles, there isn't much you can do, apart from keeping up with religious oil maintenance. That said, adhering to strict oil change intervals and insisting on manufacturer-recommended oils is your first defense against excessive oil consumption, regardless of the type of car you own.