Theory for oil level increase

[Arde]

I am used to cars that do not consume oil showing a lower oil read after a very long highway rides. The theory I heard is that a long trip causes water that was part of the oil to boil and evaporate...

Anyway, I drove the E39 M5 to San Diego (about 8.5 hour drive) and the level appeared to be higher than when I left. Coolant level is fine, no drop. Is there a theory for this increase? I know the M5 has a much more complex oil sump system, could the oil have been hiding in sumps and only came out on a long drive?

 

[deQuincey]

very unlikely
as you have mentioned coolant level fine, that in any case would have produced milkshake
does the oil smell of gasoline ?
wish it is only a misreading ;-)

 

[Gransin]

I’ve had this problem with a Nissan Skyline R32GTR I previously owned, fuel slipped down by the piston rings causing the oil level to appear a little bit higher after a while.
But it was very clear what the problem was, as the oil smelled badly of gasoline and became thinner than it was supposed to be.

 

[Ohmess]

My e39 540 has a similar engine. I wonder if the check valve at the bottom of the oil filter canister doesn't work as well after longer runs. This would allow oil normally held in the filter housing into the engine, enabling a higher reading (even though the volume of oil hasn't changed).

 

[Arde]

Thanks for the theories. The oil looks and smells fine, I need a theory that explains why the oil level would go slightly down when doing 10 trips of 50 miles vs. slightly up when doing one trip of 500 miles. I believe, and will try to prove, that the increase is a one time event. I noticed it after the first leg of the trip to San Diego and the level is the same after the second leg home.

Anyway, here is a picture in case you are a medium...California in November looking like New England in September.