When changing the oil, how important is it to drain the crankcase oil? It seems last time I changed my oil less than a 1/2 quart came out of the crankcase....also, just recently I forgot to drain the crankcase oil, but changed everything else out.......should I re-do my oil change, just drain the crankcase or leave it alone?

I did, I’m just going to re-do everything, oil filters and all......that’s what I get for not paying attention....

Agree - just cut the interval. Oil changes do a few things: get dirt out of the engine, get worn out oil out and replaced with fresh oil, get metal and other drebis out, get water out. So you just removed maybe 80-90%. So I would just cut the interval down. Oil changes aren’t always even 100% changed anyway. There is always old oil left somewhere in the engine, oil passages, oil coolers and lines, etc.

I don’t think oil ever wears out, per se, it just gets dirty and full of contaminants.

Thanks guys.......I’ll just cut the interval in half...I agree with Murphyslaw1978, I believe I got 80-90% of the old oil out.....should be ok, unless someone says different....

Listen to Steve. We have air cooled cars. Oil is motor life.

I guess it depends on what is meant by wear out. Oil is a chemical formulation mixture. If we are just talking dirt that can be filtered out by running the oil through an intense filtering/cleaning process, then correct, oil doesn’t wear out.

If we are talking contaminants that change and break down the additives and can change the chemical formulation of the oil, then that that level of wear cannot be fixed no matter how clean we make the oil unless we put back those missing additives.

There are some that say that even the base stock oil can break down under intense temperature and pressure, but that’s usually under race conditions, not on the street.

I just changed mine yesterday. Entire process really doesn't take that long. However, adding the last four quarts of oil takes a lot of patience. I feel so much better about myself now that it is done.