poikids, I own a 1992 300CE with 158,000 miles and oil consumption might be 1/2 quart every 5,000 miles. Valve stem seals are a possibility. I run Mobil 1 15W50, change oil every 7,500 miles and fill to the mid-point on the dipstick marker. Trying to maintain the oil level at the full mark could be contributing to your excessive oil consumption.

Other possibilities are leaking head or valve cover gaskets. I presume your engine has no leaks. Our daughter's 1991 300CE's engine had a significant oil leak before the head gasket was replaced.

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Fred Hoelzle