Propane is a wonderful fuel. I built a home made unit and ran a duel fuel system on a truck for over 100K with no problems. Duel meaning I was either on one or the other, gas or propane. I could switch on the move without missing a beat.

I don't know about mixing with diesel, but as a previous poster stated, there are problems having a tank in the car. I remember that someone, either the feds or the state required the trunk to be thoroughly sealed from the interior and vented to the outside.

Also, my state of Mississippi required that I purchase and display an LP Fuel decal on the rear window. It was $100 a year. Mileage in other states may vary.

Without those two details taken care of, propane folks would not fill your tank.

Harry
86 300 SDL