Mercedes 300E 24 Valve ...Burning Oil ??

Hi
I live in Australia and have a 1990 300E 24 Valve.
I have just had the car converted to run on LPG.
My car has 200,000 km on the clock and a FULL service
history.
My problem is that the car is using oil like there is no tomorrow !
It just had its 200,000 service and I have done about 1000k since and, on checking the oil, I see it is very low.
I checking it when it left the service centre and it was fine.
The car does not leak a drop of oil.
It does not blow smoke from the exhaust or " breath " oil from the oil filler cap at all.
My question is : Where is the oil going or being used ????
Thanks,
Neil
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Your message suggests the oil consumption began suddenly and recently.
Correct?
Did it begin immediately after the LPG conversion?
If so, that conversion should be investigated.
Otherwise, the usual oil consumers are the valve guides and the piston rings. The valve stems have plastic seals at the top of their valve guides. The seals wear out and allow oil to be sucked into the intake ports. The driver usually doesn't see any smoke in the exhaust. An experienced M-B mechanic can replace the seals without removing the cylinder head. Be sure he's done one before this one.
The piston rings are usually OK for many miles unless the engine is badly overheated, then they lose their temper and must be replaced.
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HI
The oil loss was well before the lpg conversion.
I have noticed in the service history that both mineral and synthetic oil have been used at different times, which ppl tell me can cause the bore to glaze and allow oil to pass ?? Any opinion on this ??
Thanks
Neil

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I've never heard of cylinders being glazed by oil, either regular or synthetic.
Suggest you have the engine's compression tested by a "leak down test" which will determine two things: a) the engine's compression - cylinder by cylinder, and b) if the compression is low, the reason - piston rings or valves. Obviously piston rings means an expensive engine rebuild.
If the piston rings are proven to be OK then the oil consumption can only be from worn valve stem seals - and that will be the good news for that job costs between $350 and $600, depending on the shop.
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Thanks T.G.......
There is no sign whatsoever of the burning oil coming out of the exhaust of the oil filler cap...is this usual ???
Hope upon hope that it is just the valve guide seals.
Would it be usual for a 200,000 k, fully serviced Benz to need rings ???
Thanks again,
Neil

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Much more likely to need valve guide seals.
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Thanks TG....really appreciate your help.
Neil

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It seems unlikely that valve guide seals are the cause of massive oil consumption if the engine is not smoking..particularly on deceleration. This engine is notorious for head gasket problems. Could the oil be leaking into the coolant because of a failing head gasket? BTW, my 24V 300CE has 160,000miles on it and uses a quart of oil every 1500 miles so I would not call your oil consumption "normal".

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rear main seal?????
the case, minus a few cans!
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