The problem with any oil is the contaminants it picks up from blow by etc. If you could filter that out while running, you could go considerably longer between oil changes. Problem is, the more filtration, the less flow you get through the filter. While changing the filter every so often may be a good thing, I prefer to change oil and filter every 5000 miles using Mobil 1. I used either Pennzoil synthetic or Mobil 1 in my 2000 V6 and it didn't leak or use a drop after 177,000 miles. It'd still been running if it wasn't attacked by a telephone pole.
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RE: does Synthetic oil go bad - 
