My dad was at taco bell the other day and saw a guy behind it pumping used vegetable oil into his fuel tank. This person was driving a late model dodge (latest body style) with a cummins of course, so my dad went over and asked what he was doing. He told my dad that he mixes 25% diesel with 75% vegetrable oil to run his truck. Anybody else ever hear of anything like this?  

It is called "blending" look it up for more info or email me direct docfranco at yahoo..he was using WVO to blend with diesel or biodiesel can be used. It works in warm climates best. I hope he was in a 98 Dodge 12V, the newer 24V cummins have a very high pressure injection pump and it does not like blending or biodiesel not up to specs.
I will probably be doing some in the mog..the mercedes diesels are well known for burning kerosene, or most any oil....lol

ps, its not generally a good idea to pump it directly into the tank with out de-watering and filtering well..  

would i be able to blend if i was running let's say a cummins 4BT?  

here is my first basic search
http://www.4btswaps.com/forum/archive/index.php?t-1086.html  

one guy in that thread says his buddy ran veg oil with 10% gasoline for 100,000 miles no sweat on an old suburban, maybe a non electronic 6.2 or 6.5?

i am ready to just say screw it, bring on the turbo diesel, nv4500, np205 and a set of rockwells haha