It used to be a sign of a worn engine, the regular top-ups of the thickest oil you could find to counter a cloud of blue smoke or regular driveway oil slicks.
Owners would even take pride in the fact that their car didn’t use a drop of oil — a great selling tool.
The fact is that all engines burn oil. A majority of vehicle manufacturers would even consider one litre of oil used per 3000km to be acceptable. This is a hard pill to swallow for those accustomed to minimal oil use, who associate oil use as sign of engine wear.
But why? The consumer demand for lower emissions and increased fuel efficiency has prompted manufacturers to rethink engine designs. One
of the best ways to increase efficiency is to minimise friction.
The highest friction point in an engine is the point where the piston rings are in contact with the cylinder walls. The higher the ring tension, the more efficient they will be at scraping oil off the cylinder walls on the downward stroke of the piston.
In order to reduce friction and achieve additional fuel economy, engineers have reduced the piston ring tension.
This has resulted in small amounts of oil getting past the piston rings into the combustion chamber where it is burned. This is the primary cause of normal oil consumption in most properly serviced vehicles.
Another change that has affected oil consumption is the move to lighter/thinner motor oil, with extended service intervals.
Oil recommendations are shifting towards lightweight grades like 0W20 or 0W60 (previously 5W30 to 20W50) to reduce friction and better lubricate internal engine components in cold weather.
This lighter oil has a tendency to get by the piston rings and into the combustion chamber.
The use of these lighter motor oils has resulted in oil escaping through oil seals and gaskets, which is usually not a problem with heavier weight motor oil.
In an ideal car sales world, the customer would be alerted to the fact that modern vehicles have potential to consume oil. But on the other hand, if a dealer alerts this to a potential buyer, it may just send them running.
So it’s a case of re-establishing a new “norm”. We’re saving in fuel and emissions, but at the cost of a few engine oil top-ups.
If your car is under warranty and using “excessive” amounts of oil, make sure your concerns are on record with the manufacturer and in writing. You never know when there could be a problem that needs resolving down the track.
AA Motoring recommends checking your oil every few weeks. Remember that oil consumption is generally not a problem — especially if the amount used is not getting worse. One litre per 10,000km these days would be considered excellent.