Occasionally, I have noticed a small puff of blue smoke emit from the exhaust pipe when starting out from a light when the car is warm. The engine uses approximately a quart of oil every 3000 or so, its a 90 420SEL. It just received its 165K EZ service and everything checked out fine. Is this puff ok, or a sign of trouble??? Thanks for your help.

Sounds like you have the same problem as I had with my 2.6 190, ie. worn valve guides.
I completely overhauled my cylinder head now no smoke and, as yet oil consumption zero!
Not to mention the improvement in performance!!

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Typically worn valve guides exhibit a puff of smoke when starting the engine when cold. With oil consumption being one quart in 3,000 miles, I would say this would be unlikely.

Best of luck,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles