I second, or is it third, the idea of using one of the diesel rated oils. I bought a 1989 300SE in March and did the oil changes with Penzoil 10W-40 until the last one, when I switched to Chevron Delo 15W-40.

Since I owned it the car has used about 1 quart per 1,000 miles, though it doesn't smoke and the plugs are clean. Since switching to Delo the oil level has scarcely moved since I changed it, 1,500 miles ago.

Like Nipperiley, I've just started pumping the oil out through the dipstick tube. With the top mounted oil filter, it makes oil changes super easy, quick and clean. I pump the oil into clean gallon milk jugs and drop them off at my local Auto Zone.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire