I have a friend who drives an early 2000's RAM diesel. He bought one of the waste vegetable oil (WVO) kits that mount in the bed of the truck. When he starts the engine, it warms up and switches to the WVO tank, which contains raw (but filtered) veggie oil right from a restaurant's fryer. It runs on the 100% WVO (through the stock fuel system) while he's driving. When he stops and turns the engine off, the valves change back to pump diesel and the engine runs for about 3 minutes to purge the fuel system. So he starts and stops on pump diesel, travels on WVO.
He loves it and has a few local resturants provide him with all the WVO he can carry off. He just uses a Baja filter and dumps the resturant oil right into the tank. When I talked to him about it a couple months ago, he said he just sticks to RAM's normal maintenance schedule, nothing added or altered. He said he does lose about 3-5 MPG but when you're running free fuel, who cares?!
I'm seriously considering adding a WVO kit to my truck. Only problem is, resturants now know the value of their WVO and typically charge for the oil. Chain resturants in my area want a contract to pick up the oil (usually 100-200 gals at a time) on a regular basis (sometimes weekly) and pay them for the oil. Kinda throws a wrench in the economic side of WVO systems unless you are burning a couple hundred gallons of diesel a week.
BUT long story short, Bob's been driving his RAM for over 20 years with no issues from running WVO.