I am not trying to put anyone's advice down, but heres some food for thought- It would take 40 hours to travel 3000 miles going 75 mph, now I consider that the car doing that would be at 2800 rpms under a light load, my boat on the other hand generally operates at 3500-5000 rpm's under a heavy load. Not sure if my thinking makes sense to anyone else, but oils cheap and I change mine at around 20 hours, which runs me about $60. in oil changes per year.