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Hi All

When I bought my 99 M5 a couple of years ago at 47k miles it drank a litre of oil every thousand miles. I noticed it improved quite quickly and in the 50 and 60k miles I was adding a litre every 3000 miles.

I hadn't really monitored it closely, but I just checked the oil level this morning (104k miles) and it's about 1/3 off the top, and the car's gone about 4000 miles since the last service...so at this rate I'll get about 12000 miles out of a litre.

Dealer uses Castrol RS 10-60, and I top up with Castrol RS.

Has anyone any idea what can cause a 12 fold improvement in oil consumption over 60k miles ??

Thanks

Guy
 

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Guy10 said:
Hi All

When I bought my 99 M5 a couple of years ago at 47k miles it drank a litre of oil every thousand miles. I noticed it improved quite quickly and in the 50 and 60k miles I was adding a litre every 3000 miles.

I hadn't really monitored it closely, but I just checked the oil level this morning (104k miles) and it's about 1/3 off the top, and the car's gone about 4000 miles since the last service...so at this rate I'll get about 12000 miles out of a litre.

Dealer uses Castrol RS 10-60, and I top up with Castrol RS.

Has anyone any idea what can cause a 12 fold improvement in oil consumption over 60k miles ??

Thanks

Guy
Ignoring oil leaks & drips from seals and gaskets, oil comsumption should not increase unless a car has abnormal cylinder wear, cylinder varnish or ring land deposits that would impede the piston rings ability to maintain seal against the cylinder bore.

A well-maintained and serviced motor on premium synthetic oils should not show an increase in oil consumption until well beyond the 250K mile mark. At this point, cylinder roundness & clearances and ring tension will "begin" to deteriorate to the point that it has a negative impact. This goes for a $15K 6 cylinder Ford car or a $100K Mercedes.

I am not a "fan" of the alusil/nikasil BMW cylinder design. It can show accelerated wear compared to steel sleeves or iron block designs. I still feel the alusil motors can last well beyond the 250K mi mark without cylinder problems. Certain S62 motors may have a ring tension issues, I'm not sure. Some '97 and '98 M62's are approaching 300K mi without issues.

Oil consumption of a used car with moderate miles can drop over years due to many variables:

1) The original owner drove the car differently. Under this scenerio, the original owner putzed around at light throttle and the engine saw more ring land buildup and varnish. Over time, this buildup can dissipate if the new owner occasionally drives the car like he stole it.

2) The original owner used a different type of oil. The new oil could have improved detergency or produce less deposits. Over time, the old deposits could diminish and ring seal could improve.

3) The original owner used a different service interval. If you switch from BMW's 15K or so oil change cycle to some aggressive schedule, the detergents & additives in fresh lube could flush the varnish and other crap out of the motor and improve ring seal.

4) A different brand of gas can affect ring land deposits which impacts oil consumption and blowby.

5) Driving behavior & use greatly affects oil consumption. Oil use will be minimal if the car sees long trips under light throttle. Oil consumption will be highest when the car sees hard throttle and/or short trip use.
 
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