Losing oil?

Honest John Back Room » Technical matters
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Wed 18 Feb 2004 16:10
Losing oil? - Roger Jones
This tip comes from Paul Gibbons in an MB W124 discussion group, with his permission. His disclaimer is "this opinion has been formed over 33 years of tinkering with cars, not cast-iron facts passed down from on high". If he's right, it's very useful; if he's wrong, I'm sure we'll hear from some of the technical experts in the Back Room.

"To diagnose where the oil is going, find a long hill and get up to a reasonable speed at the top of it, say 120mph (alright 50 then). Drive down the hill on a trailing throttle.

At the bottom put your foot down and watch for smoke from the exhaust.

If it smokes a lot in this situation it's almost certainly the valve guide seals (but check the PCV plumbing just in case).

If it smokes when accelerating most of the time, it's probably going past the rings."
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Wed 18 Feb 2004 20:30
Losing oil? - Dizzy {P}
This sounds about right for older cars where a high depression in the air intake system can cause oil to be sucked past the inlet valve stems. I'm not so sure about newer cars that may have devices to prevent high intake depression in the interest of reduced emissions.

For example, 25 years ago some carburetted cars had little poppet valves within the throttle butterfly valve to reduce depression on the over-run so as to lessen emissions.

Flatlanders like myself who have no local hills could try sharply decelerating on the flat and in 3rd gear from, say, 70 to 30 mph and then accelerating again. This should give the same results, i.e. smoky exhaust if the inlet valve stem seals are badly worn.

All this applies only to petrol engines of course. Closing the throttle on a diesel interrupts the fuel supply but still allows full air flow.
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