Rotella 5w40 "synthetic" is what I've been using for about 2,000 miles so far. It's not *full* synthetic but mostly synthetic. I used to use Delvac 1300, and I don't see much difference from it with Rotella as far as engine noise and soot are concerned. The car didn't smoke with Delvac, and it doesn't smoke with Rotella. The only real reason I switched is because I don't want to change oil every 3,000 come winter time... Hopefully 5,000 would be fine on Rotella. I haven't seen Mobil1 SUV and Truck locally...

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84 300SD - bought in April '06 with 237,000 mi