The truth about oil consumption in modern cars
Does your car have a drinking problem? A destructive relationship with engine oil? Is the manufacturer brushing you off as your car burns oil between services?
Plenty of people complain to me about this. Here are the facts.
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?” - LUKE
To do this question justice we need to do a crash course in engine design basics - past versus present:
OLDER ENGINE DESIGN
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.
TACKLING FUEL CONSUMPTION
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.
At the risk of sounding like Morpheus, feedback is everywhere. It is all around you. When you go to work, when you pay your taxes, and when you help your landlady carry out her garbage (I think that last one was actually Agent Smith). Anyhoo…
Feedback is the reflective effect of changing a system. It can be positive or negative, expected or a complete shock. This issue is entirely expected, and ngative.
It’s like this: If you are caught pumping up the boss’s secretary, because (I dunno) maybe she keeps going down on you, and nobody likes a deflated PA, then the primary change to your system is all the enjoyable recreational third-party inflation, and the feedback effect is being kicked out of the family home and seeing your kids every second weekend for the next 15 years - if you’re lucky.
So the feedback here is oil consumption, off the back of reduced friction. But this oil consumption is not like 1980 engine Batmobile smokescreen ‘engine pooping itself’ oil consumption. It’s not indicative of early wear or a defect unless the consumption rate increases substantially. It’s just how your engine rolls.
Frankly, I don’t believe it’s that much of an imposition to tip in one litre of engine oil every six months (which for ordinary drivers is about 7500km). Especially since, whatever the oil costs, you’ve saved more in fuel than that.
Manufacturers are very bad at communicating this - because any way they sex it up, it would turn some subset of potential buyers away. If a manufacturer alerts you to the potential oil burning effect pre-purchase, some potential owners will run.
So they talk up the fuel efficiency and shut up about oil consumption.
Frankly - many manufacturers are also fairly crap at the implementation of expected oil consumption. And dealerships are often bad at the hands-on aspects with confused customers.
In R&D they should be smart enough to build additional sump capacity into the engine, so that (say) a design limit of two litres of in-service oil consumption does not take the dipstick from the ‘full’ mark to the ‘add’ mark between services.
They need to make this a non-issue for owners. This would be a robust, responsible way to deal with the issue. If they did, for most owners, it would become a non-issue overnight.
As things stand, it’s nuts to impose this mid-service-interval ‘add oil’ responsibility on owners - and yet it appears to be a standard operating procedure for some companies.
There’s also something intrinsically shifty about the entire awareness and communications process. It’s almost as if they’ve become so adept at bullshitting you that they use bullshit even when complete honesty would serve everyone better.
And the feedback for them, ultimately, is customer dissatisfaction blowback. Often to the extent that the customer never buys that brand again. So easy to fix...
WHAT YOU MUST DO
My advice to you, if your engine has a thirst for oil, is this: get your concerns on record with the manufacturer, in writing, in case there is a problem and it needs resolving after the warranty expires.
Check your oil regularly - not that hard, and a good idea once a week. Remember that oil consumption is generally not a problem - especially if the rate of that consumption is not accelerating. If it’s one litre every 10,000 kilometres (or whatever) then that’s a relatively good sign.
And remember that while you’re bitching over the service counter about this alleged drinking problem, it’s also actually saving you cash.