The Rule of Thumb i always heard for diesels were.. if your just driving around locally, or longer hauls under a few hours on the highway empty or moderately loaded you can shut them down with no issues... (now an 8 hr or so trip of all highway, high RPM runs let it run for 10 mins or so)... if your pulling heavy loads (5th wheels, heavy construction equipment, max load pulls) on the highways for long periods of time its better to leave them running while your fueling. Reason being is to protect the turbo. very little oil remains in the turbo once the engines shut off.. because of this youll end up boiling the oil away from the bearings leaving them unprotected when you go to restart the engine later.

 

i have that issue even when the trucks been shut down completely for awhile... i knew the tank was full as i just filled up.. had stopped somewhere else and when i jumped back in the truck the gauge only read 1/2 tank... 1/2 hr down the road the needle jumped up to full and started reading correctly... ticked me off the first time it happened as i thought someone siphoned my tank while it was parked out of site.. from what ive read on other forums its a common issue with the superdutys..

 

I always refuel with my truck running but I fuel at my own tank which is a hand pump tank so I leave it running with the drivers door open to watch the fuel gauge. This way I don't pump my fuel on the ground.

 

Never refuel running. I ALWAYS check my oil when I buy fuel. I always have in every vehicle, motorcycle included. With the fuel lines and injectors under the valve covers on the 6.4, if I ever had a leak or oil dilution. Issue, I would spot it at fill up.