same engine in a work environment will have a 250 hour or 15000 mile interval and if using quality synthetics can up that to 400 hours or 20000 miles
i run my delivery trucks 12000 miles between changes and I use the best oil I can buy , Amsoil
I use it in my motorhome too but change every year , but the used oil goes into another older vehicle , hows that for recycling
I also got 10.4 mpg average on a trip last week from detroit to alberta