Synthetic oils.

I wonder if there is a little vacuum forming in the dipstick tube by sealing off at the top and drawing oil up the dipstick tube, I suspect that happens with my Nissan 3.00.

Hi Axle,
Like every thing else, I would imagine that it expands when it's hot. Thats why you always check your auto trans fluid when it's hot, and maintain the correct level in heat because the level is criticle in a transmission, but not so criticle in an engine. Perhaps synthetic oil expands more than mineral oils.

Chaz

How much of an increase - 1mm , 5mm?
Have had it happen on a worn engine with petrol getting in the sump, but yours is not worn.
You would think that if the first check was when cold, and the 2nd check was when hot, that the hot reading would be lower due to the oil moving to the heads while running. Especially being a horizontal boxer motor. How well do the heads drain back to the sump? Is there a build up of oil in the heads when cold?
What does the manual recommend? Check when cold or hot?
You did wipe the dip stick before dipping and taking the reading both times?
Silly question I know, but it does make a difference after some oil surge.
5 hours should be long enough to get the engine hot to evaporate off any water and petrol in the oil too.

Hi Axle,

Dont know if this is a cause but I have a subaru 3.0RB and was told by dealer the correct mobil synthetic was the new one in the gold container which I think from memory is 10w30. Of course it more expensive than the other.

Cheers

Kevin