On steep grades, oil will "hang" in the valve cover at the rear. It normally drains back down the chain case in the front of the head.

Three posibilities -- worn rings (but you would see smoke at high load all the time, and burn at least a quart in 500 miles all the time), bad valve guide seals allowing oil to get sucked down the valve guides under the conditions you describe (possibly also worn valve guides, too), or bad valve cover gaskets that allow the oil pooling in the valve cover to run out on the exhaust on steep inclines. Hard to tell from inside the car, you will have to look under the hood and check for charred oil in the exhaust manifolds.

If you have excessive blowby from worn rings, there will be large amounts of oil in the air filter housing, too.

Expect to do chain, valves, and guides around 250,000 miles on that engine.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!