Oil Consumption in Modern Cars: The Truth
Does your car have a drinking problem? A destructive relationship with engine oil? Is the manufacturer brushing you off as it churns and burns oil between services? Plenty of people complain to me about this.
Here are the facts.
Now look - there’s nothing I like more than the repetitive application of lubricant. Maintenance is very important.
Frankly I get several hundred complaints by e-mail about alleged excessive oil consumption. Often in relation to Audi, Holden Colorado, and Subaru.
Luke’s question on this is typical - I’m just picking his because it’s the most recent. And he’s literate - he uses sentences and everything, which is not always the case.
“I have a 2014 Holden Colorado with 67,000km on the clock. I’ve owned it since new and it is using two litres of oil between 15,000km services. Car has been fully serviced. Holden has replaced the dipstick and continued to monitor it for a year and have now put 5W40 in it at the last service but it hasn’t helped. I have recently been told in writing by my local Holden dealer that “Anything below 2.5l per 10,000km is considered acceptable, and additional top ups between services are not uncommon. Is this reasonable?”
To do this question justice we need to do a crash course in engine design basics - past versus present:
In the past, engines were built tight, and they consumed, essentially, no oil for years (if you maintained them). Then, inevitably, wear would overcome them, and the piston rings and/or valve guides would give up the ghost.
After 150,000 kilometres, or whatever, mechanical wear would take over, blow out the clearances, and as a consequence, a great deal of engine oil would burn, and every takeoff at the lights would make you look like the Batmobile in ‘smokescreen’ mode.
Wear would then accelerate and your engine would be a dead man walking.
Then, about a decade ago, maybe 15 years, manufacturers started to get real serious about fuel consumption, and there are three ways to tackle that.
The easiest way is just to make cars lighter - but since that also makes them, typically, smaller, and less brimming with the cool toys you expect, manufacturers are disinclined to do that. Cars keep getting bigger and heavier.
The second way is to improve combustion efficiency - which is what variable valve timing, direct injection, variable geometry turbos, etc. - all the cool engine engineering toys - are about. Burning the same amount of fuel and extracting more useful work from it.
And the last way - in many ways the most accessible way to make real efficiency gains - is to tackle resistance. Things like aerodynamics, rolling resistance, and internal friction. Losses. These are the things you can’t feel, but which your engine needs to battle every rev, just to get your car out of the blocks and moving.
Internal friction in your engine is one of those big-ticket ‘losses’ items. So, in an effort to reduce fuel consumption, manufacturers have for several years now waged war on internal friction in engines, and they’ve wound back the tension in the piston rings and valve guides, in particular.
This saves fuel (and it saves you money - let’s not forget that while you’re bitching about oil consumption - you’re saving money on fuel here) but it also opens the door to oil consumption. And this understandably sets off warning bells in some owners’ minds at least.
This oil consumption is a feedback effect - looser piston rings and valve guides slide easier but allow some oil to be burnt. Classic example of an overall positive change also generating negative feedback.
