Joe,

Count me as a skeptic for the moment.

Assuming you intend to do this try to establish a good database. In my plane and bus I record every single gallon of fuel that has ever passed through them. I do that primarily to establish what is normal, and if anything changes it shows up right away in consumption.

Why I don't see this propane as a money saver is my belief that you cannot get something for nothing. Your diesel fuel has a specifc BTU content and that defines how much work it will do per gallon. You can increase the efficiency to an extent with driving practices and by making sure the engine is using the fuel efficiently, but in the end it is all about BTUs.

When bio-diesel came to our area the news media was all over that story like stink on a skunk. We were going to save the planet and it was cheaper. Then some smart ass reporter did a little digging and found the numbers did not work. The new fuel was not giving the same mileage as pure diesel fuel, and when the cost per mile was calculated it had actually been more expensive. The other factor was the range due to the lower efficiency of the fuel so drivers had to fuel up more often.

When you add propane you add something with less BTU content than diesel. As a result something is going to be less efficient. Now if your truck is running lean (something I would expect so the efficiency is greater) and you add a greater fuel charge to the cylinder the truck will feel more powerful, but is the work performed going to be greater than the cost to do the work with pure diesel?

Unless you have detailed data of an unmodified truck to compare to one modified, and the operating parameters are unchanged you can only guess at the results.