checking oil quality
What I did was to immediately check the color of the oil which the dealer
Claimed ti done the oil change. I found that either they did not wait
Long enough to be sucked out or drained. The oil was still
Black immediately after they claimed it was changed.
You can send out the oil for analysis which gives the
Composition especially if there are any metals.
Generally what wears out is the additive package in
Synthetic oils. What drains out the last is basically more
Of the sludge etc.
I generally change the oil out myself every 4000 miles.
Because I get the oil relatively cheap at $5.95 per quart
From my sources.