'92 Aerostar with 117,000 miles. Current fill is Redline 10w30. The oil was changed Oct 05 and now has 8 months and 4000 miles. I used a Maxlife Filter, oversized (FL1A size instead of spec FL400 size). Since the oil is Redline, I am wondering if the filter may be getting clogged from the cleaning effect (not here to debate whether or not Redline actually can clean an engine). Past two OCIs were Group III synthetic. Prior to that it was Durablend or Maxlife. Anyway, I was going to run this oil for a year, but see no reason I could not go beyond a year to 15 months or more. Has taken 2.5 quarts makeup oil since Oct 05, so there is a lot of freshening up going on and if I spin a filter, there will be about 26 oz more fresh oil.