Was the oil there and then not there, or perhaps not really fully filled
the last time it was changed? I've known a bubble to form making it look
as if the sump is full - until the engine is run, when the bubble bursts
and the oil level drops in an instant. (But that was a dirty old Ford
side-valve engine, probably full of gunk - and it had an oil filler tube
that smoked like a chimney).
The classic beginner's mistake is using the dipstick while the car is not
level; another one is to check the level while the engine is cold, then
while it's hot and the oil hasn't yet drained back into the sump.
If oil really is being lost it must be going somewhere! Any idea how much
is getting lost in a given time or distance, or if the level drops while
the car is parked? Is the radiator level stable and the coolant clean?
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-- ^^^^^^^^^^
-- Whiskers
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