Hi! Some blow-by is normal on an old diesel, and most of the oil is thrown out by the timing chain when you lift the lid. there is less blow-by under load (driving) and more at idle (when you check)
Does it blow oil into your air cleaner?
How is your oil consumption and cold starting?
And what is it's mileage and how has it been serviced? (oil changes, valve lash adjustments?)
VERY high oil consumption and difficult cold starting are signs of engine wear..
I just bought the car and the guy was Korean and spoke little English. I could get only limited information from him. I asked about history but he gave no discernible answer.
The air filter is clean, though it appears new. There is definitely oil inside the oil filter compartment, however. Not sure how old and how long it's been there.
As for cold starting, it has not had a chance to be started in the winter. (I bought it two weeks ago.) The mileage appears to be 1.1 million (odometer: 136,000). And the oil consumption is hard to tell because it leaks.
Here is what I do know and what I can tell you to help me:
The engine does not smoke badly at all -- no white smoke and no black smoke almost at all.
The car's biggest problem (to me, at least) is that it struggles uphill, moving only 35 mph or so and hesitating very badly. On flat surfaces it drives almost perfectly. It's the hills (and grade, even the slightest) that slow it down. I can't even get on the freeway, given how dangerous it is to drive slowly there.
However, when I fill the tank up, it does drive better, tackling hills much better but still not at full power.