I think there must be a engine internal oil leakage causing oil from somewhere? in the upper parts of the engine to very slowly leak down into the sump.
But what could that be ? ? ?
It's an Astra-G with a Isuzu 1.7 diesel, fairly standard/simple engine I think. It does have a turbo, and a EGR valve. There's no other faults or symptoms.
The Haynes? book says I should measure the oil level 10 minutes after halting, so that's what I've done, and it's half a liter above min (or half a liter below max if you like) 10 minutes after halting.
But if I then come back a couple of hours later, it's aprox half a liter above max ! ? ?
I'm fairly sure it was not like that before, and this is my second Astra with this engine.
Before this I had oil and filter change of course. Could it be one of the oil filter gaskets ? Or a not quite compatible filter ?.
Also before this, I had a too high oil level so I sucked out a little bit using a break fluid vacum pump/hose through the dip-stick (simple and easy).
And at the same time before this I had an EGR-error indication, so I had the EGR out (for the second time), cleaned it, tested it, and put it back in. If that was because of too much oil or just ordinary usage I don't know. It's quite a bit of work and I had to do it a couple of years before as well, so I'm generally taking care not to have too much oil on the engine. But I don't measure the volume I pour into it. I just fill it up and check the dip-stick. ... So maybe that's how I got too much.
So now, I'm using the car with maybe half a liter too much, but if I check it 10 minutes after halting, it's just perfect.
There's no other faults ! ...... Power and performance is o.k. / as normal, and coolant level is steady an nice,... there's no other symptoms that I know of. The level is always the same (except as mentioned).
These Y17DT engines (of which this is my second) both had oil leakage from the cam shaft sealing (and possibly some of the other seals as well), causing the register belt to be soaked in oil (but still running though), so for both I had to change the seals, and thereafter I generally didn't have any problems with the engine. Except for the Astra-G version which had a seal in the generator as well (between the vacum pump and the generator) that was of course leaking as well, and this #¤%&#" EGR on the Astra-G, and the ECM needing replacement on the Astra-G,... but the engine itself is, apart from this, generally quite nice.
By the way, also now (and not before),... there is oil long up the dip stick after taking it out, and I have to clean it lower it and pull it up again. I don't think it was like that before. ?. ............