Why Does Oil Consumption Happen? Is It a Lot or a Little?

Let's start with a rhetorical question: is a litre of oil per thousand kilometres a lot or a little? It depends: for V6 or V8 engines it's almost within the norm, for inline small-displacement engines it's definitely a lot. You have to understand that any engine, even a brand-new one, consumes oil. Basically, the oil in the engine simply burns off in the cylinders, staying on their walls. That's literally the oil's job — to coat every internal surface with a film and prevent dry friction. And that film burns up in the combustion chamber along with the fuel mixture.

The only question is exactly how much oil is burning off in your engine and whether you need to do anything about it. The experience of a great many used-car owners shows that even with a fairly worn engine, it's usually cheaper just to top up the oil than to do an overhaul.

That's probably the right place to start. In reality, there are a few more causes of increased oil consumption than what garage “experts” simply call a “dead” engine. Oil in the engine can burn off above the norm, or it can just plain leak. And in most engines, pinning down the real cause of increased oil consumption is actually quite hard.

What's more, some causes can only be identified by taking the engine apart, which is why mechanics, after an overhaul, often don't tell owners exactly what the cause was in their case. That's because in many situations an engine overhaul is far from the best way out of the situation.