We have 6 Promaster 3500 extended vans. The 2014 had to have a flex plate & radiator @ 235,000 miles but otherwise is still running well. It has had to have at least 10 headlight bulbs but I think that is primarily because the headlight bulbs are VERY difficult to change without touching them on something, probably contaminating the bulb, which causes premature failure. We have learned that taking the headlight assembly out increases bulb installation time to about 30 minutes but greatly improves bulb life because of a cleaner install.
All we have are gassers running 5w-20 Mobil-1, changing every 10,000 miles. We don't feel buying diesels pays off. Our Promasters have up to 250,000 miles and have had no other major problems. The 2014 model seems to have been more troublesome. Our 2015s and 2016s are doing well. We haven't had to replaces any brakes on any of them at all. Surprisingly, none have had any transmission issues, which we believed was the weak link of the drivetrain. Fortunately, this has not been the case.
You can expect up to 19 MPG if you hold it under 63 MPH, or 17 MPG if you run 70 MPH.
We put in polyurethane coated plywood floors with two rows of E-track running lengthwise mounted flush with the plywood surface. This setup works great in nearly every situation!
