I recently switched to Mobil Delvac 1300 industrial grade oil. Should I still change my oil every 3000 miles? I put on several hundred miles a week (anywhere from 200-600) so 3000 mile oil changes could get quite frequent and expensive and may negate the added cost of the better oil. Could I possibly change my oil every 5000 miles? 6000 miles?

Also, today I found a 5 gallon barrel of 15W40 Rotella oil for $40. Is this a reasonable price? I really like the idea of having a large bucket that I could keep refilling with oil and filling my engine with a hand pump (although I guess I couldn't count how much oil was going in unless I first filled a quart bottle then poured the bottle in). Thanks!

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside