All car engines burn oil.
That being the correct term, rather than “use” – which isn’t.
It’s an inevitability arising from the fact that they are designed to. Lubrication being necessary to keep the pistons from welding themselves to the walls of the engine’s cylinders. If they fit like a dowel in a piece of furniture, you’d end up with what you get when you assemble a piece of furniture using dowels; i.e., something that (hopefully) doesn’t move.
But you need the pistons to be able to move (up and down) within the cylinders, if you want the engine to run. If you want the car to move. So the pistons are just slightly smaller in diameter than the bore of the cylinders. Oil is there to prevent the two from becoming one.
It’s only a very thin – microscopically so – layer of oil and the piston rings take up almost all of the remaining (and very small) gap between the piston’s sides and the cylinder walls. But some oil remains on the walls and some of it is consumed when the spark plug fires the air-fuel mix inside the cylinder.
Normally, it is very little – as in so little you’d likely never notice it – unless you don’t change your oil more often than once every 10,000 miles – by which time you might notice the level on the dipstick is down a little.
But sometimes, it is a lot more than that. Even when you can’t see it – as in blue smoke billowing out of the tailpipe, which used to be the way you could tell a car’s engine was burning oil excessively, without keeping track of the level on the dipstick. The reason you don’ see that as much as you used to isn’t so much because modern car engines don’t burn oil. You just don’t see the result as much – because of the scrubbing action of the catalytic converters (plural) all modern cars have.
What happens is the oil that’s being burned by the engine is burned again, by the catalytic converter – which gets really hot in order to do its catalytic converting. A car’s engine has to burn a lot of oil in order for you to be able to see it – via blue smoke billowing out of the tailpipe. But just because you don’t see it happening, don’t think it isn’t happening – assuming you see the level on the dipstick going down and there’s no puddle on the ground.
And if it is (and there isn’t) it’s bad – and not just because it indicates an excessively oil-burning engine, which is also an engine that is losing compression – which means an engine that is losing power and burning more fuel to not make it. If it is burning oil excessively, it is also silently plugging your car’s very expensive catalytic converters – plural, as even four cylinder-powered cars usually have at least two. If you have a V6 or V8-powered car, you may have four of the things – two of them “close coupled” to the engine, typically integrated with the exhaust manifolds – and two more downstream. The tab to replace all four – if they get plugged up with oil/carbon residue – isn’t inexpensive.
And you’ll have to replace them, eventually – because the engine eventually won’t run at all once those converters get too plugged up. And it won’t run well long before that. Plus, you will probably not pass emissions – if you live in an area where those are required – and that also means not being to drive the car (legally, at any rate) if it fails the test.
That’s why keeping track of how much oil your car burns is important. Especially if it is a new or late-model car and still under warranty. So that if there is an oil burning problem, you don’t end up paying for it.
But how much is too much?
Some car companies will insist it is normal for an engine to burn a lot of oil, as much as a quart every 3,000 miles or so.
That kind of oil consumption indicates an engine problem. It could be poor cylinder sealing – too much oil getting past the oil control rings that girdle the pistons. Oil control rings are slightly flexible; i.e., they expand and contract, to allow the piston to move up and down within the cylinder while also sealing the cylinder enough to prevent excessive oil consumption. But sometimes, poor machine work – or low quality parts – or shoddy engineering/manufacturing/assembly – results in just that.
It could also be the result of something many new car engines are fitted with called direct injection (DI or GDI). This is a form of fuel injection that sprays the gas into the cylinders as a very fine mist under immense pressure – as high as 3,000 psi. Ordinary port fuel injection operates in the area of 35 psi or so.
That highly pressurized gas – which is a solvent as well as a fuel – can increase oil burning by decreasing lubrication, which leads to more rapid wearing of the pistons rings and cylinder walls, which leads to . . . more oil burning. Which gets worse and worse until you finally begin to see the blue smoke, which is the signal you’ll soon be seeing a big bill.
DI/GDI also increases the likelihood of carbon building up on the stems/backsides of the intake valves, which are ordinarily kept clean by the solvent action of the gas being sprayed by the fuel injectors, which are usually located just behind them – in a port fuel injection system. But DI (GDI) injectors are threaded into the cylinder walls and spray the gas directly into the cylinders. There is no “solvent effect” to keep the intake valve stems/backsides from crudding up (with carbon residue from combustion, including from combusting oil) and – eventually – they no longer seal completely when closed.
You get more blue smoke – and another big bill (to clean/de-carbonize the intake valves).
If you own a car equipped with a DI/GDI (the acronyms refer to the same thing, differently marketed) it is especially important to keep track of the oil the engine may be burning – by checking the level – on the dipstick – regularly, so as to be aware of any abnormality. You can also check the plugs. If they are oil-fouled, then your engine is burning oil – even if you can’t see it.
And burning more than a quart every 3,000 miles – or even every 5,000 miles – isn’t normal, no matter what they tell you. If your new (or new enough to still be under warranty) car’s engine does burn that much, document it – with the dealer – so that when that big bill comes, there’s at least a chance they’ll be the ones paying it.
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