The only problem I had with old veggie was animal proteins.That is the grease from fried meat.
Cold filtering sloved this problem. Also rushing to filter(if out of diesel money) caused problem with water.A Stanadyne FM 100 5 micron water seperator helps.But you need to wait a week to settle water out.
New oil never no problem as long as injectors are 175 degrees,and I never run 100% oil.I always mix 30% diesel in.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran