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My 2008 Jetta SE, 2.5L, seems to be burning quite some oil — engine looks clean, and there are no spots on the ground, but I've already added a few extra litres of factory-recommended synthetic 5W-40 (I'm not changing oil overly frequently, hence several litres of top-up).

The purpose of the oil is to clean the engine, and suspend particles, where the smaller particles are suspended within the oil itself, and larger ones are filtered out by the oil filter, per my understanding.

When the oil disappears from the engine, requiring a top-up, what happens to those smaller particles that were previously suspended in said oil? Do they burn-off, too? Or are they left behind to be suspended in the leftover oil?

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How often are you adding oil? How often are you changing the oil/filter. –  cinelli Jul 2 '13 at 3:02
    
@cinelli, as per mechanics.stackexchange.com/questions/12395/…, I add about a litre/quart of oil about every 6k miles, it would appear. –  cnst Sep 21 at 17:08

2 Answers 2

The metalic particles that are not filtered by the oil filter remain in the system and do not burn off. They usually build up at the bottom of the oil pan. Note that if these metallic particles are sucked up by the oil pump, which is very likely, it is very possible to cause damage to the pump as well as other internal components.

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I'm no physicist, but I strongly suspect that the small metalic ( probably heavy metals ) particles melt at a much higher temperature than the oil, and aren't burning off in the same way your oil is.

I'm not sure you need to worry though, your oil filter, provided you are changing it regularly, should be catching the particles that are big enough to build up in a way that would significantly shorten the life of your engine.

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