Making their own diesel, smart folks, they are, trouble is when their vehicles go buy it smells like fried chicken.
When you make your own diesel from cooking grease and put it in a car with a diesel engine, it smells like... diesel fuel. It’s no different than the diesel you buy at the pump.
You’re thinking of diesel engines that have been converted to run on grease. They also call it WVO (waste vegetable oil.) That’s the kind of fuel that smells like french fries.