Oil change interrvals
Oil is cheap, hard parts real expensive. Engines cost $4K-$34K (600's)
short trip driving in winter max 3 months.
Long (more than 15 mi) in warm weather probably OK at 5K with 10W30, 10K with synthetics. Diesel stick to MB manual max.
Highway 18 wheelers go 20-40K or more, but have comprehensive oil analysis, large filters, large sumps, and often run up 3000 miles a week!