My car normally has a clean smoke-free exhaust, except for some times in the morning while the engine is still cool. One route to work goes down a short steep hill with a stop at the bottom. When I accelerate from there, heavy clouds of blackish grey oil smoke pollute the air for a few hundred yards. Then it clears up. If I take another route that avoids the hill, there is no smoke at all.

What mechanically causes this? A combination of worn valve seals and a downward angle? Oil pump issues?

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma