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      02-08-2012, 11:29 PM   #1

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Reason for Oil Use

I just had to put a quart of oil in my engine for the first time since I owned the car. I had read that this is necessary. However, I was wondering why this is.
I'm new to the site so don't flame me. I'm sure there is an simple answer as to why the engine is designed to use oil. I just want to know the reason.

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      02-09-2012, 02:22 AM   #2
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E90 M3 Jerez Black/Bamboo Beige 6MT - BMW CCA
Dinan Rear Exhaust, Secondary Cat Delete, Dinan High Flow Carbon Fiber Intake, IND Painted Reflectors, BMW Edition Grills
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      02-09-2012, 11:04 AM   #3
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no reason... our cars just drinks oil period.... LOL

i put 1 qtz of oil every 7-8k miles.. some add 3-5... depends on how you drive...

always carry a qtz in the trunk just incase...
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      02-09-2012, 03:31 PM   #4
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Here's a post that I wrote in the thread posted above that explains the technical reasons for oil consumption:

Originally Posted by M3PO View Post
Oil consumption is caused by a few different things.

One of them is blowby. Expanding gases in the combustion chamber blow past the piston rings and entrain some of the oil lubricating the rings. This oily blowby is then evacuated from the crankcase by the PCV system and returned to the intake system; the oil is then burned in the combustion chamber.

Reverse gas flow is another one. During evacuation of the cylinder during the exhaust stroke, the cylinder pressure is actually lower than the pressure between the first and second piston rings. This causes a reverse flow of gas into the cylinder and it "sucks" some of the oil in liquid and/or vapor from the piston ring system into the cylinder.

Oil is also consumed as acceleration and deceleration of the piston throws oil from the top ring land into the combustion chamber. This is called "throw-off". Throw-off type oil consumption is worst at low loads.

In a similar way, aggressive driving can cause increased oil evaporation from the top ring land. Consumption due to evaporation also takes place at the cylinder liner. It's magnitude is highly dependent upon oil composition.

In older engines, there was some oil leakage from the valve guides but newer valve seal designs have virtually eliminated that as a source of oil consumption.
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