This unfortunately is a symptom of a rupture in the engine
block/head cooling system such that it's getting into the
oil system. For example, a head gasket leak.

Check
-- the appearance of the coolant in the radiator, via the
radiator cap, in a cold engine. Same for the coolant
reservoir. If oil is present, it's looking like a head
gasket or similar leak.
-- the appearance of coolant in the oil system. Look into
the filler cap hole and check the dipstick. Look for foreign
residue on the filler cap (white?)
-- Does the car's exhaust smell like anti-freeze at all?
-- Look for foreign residue (white?) on the spark plugs.
-- Is the car overheating at all.

I would not drive the car further until this is resolved. Or
certainly do not let it overheat. This will worsen the
problem and make it more expensive to fix.

"Pauly" <paul.jonaitis@gmail.com> wrote
>I have an ongoing oil consumption problem in my 99 Accord
>(4 cyl). The
> car has 88k miles.
>
> Yesterday I checked oil after the car was parked for about
> an hour (on
> a very hot day) and the level was below the lower mark.
> This morning I checked it again (the car was parked
> overnight, so the
> engine was completely cold) and the level was almost at
> the full mark,
> about 90% full. How is this possible???
>
>
> There are no drip or leak marks under the engine or in the
> engine bay,
> last oil change dealer could not locate any leaks (oil pan
> seals, etc),
> so they asked me to start recording oil levels when I fill
> up gas.
>
> Any explanations for such fluctuation?
>