Well I've been wondering about this for a while. I run Mobil 1 in my Z and have in the past changed the filter and added ~1qt @ 5K mi, then change it all at 10K mi.

Now, I have 13K mi on the oil and am about to change the filter again here soon in 2K mi... I looked at it and it's still a medium to dark brown, not black at all.

Would it be safe to push it to 20K mi changing the filter and adding a quart every 5K mi? Or is that a big

The vehicle still runs strong and all...

Input is appreciated...