Will an Isolation transformer save fuel? Let's find out together.

I'm using a Wacker Neuson Light tower, LTN6 as a generator. It has a 6kVA generator head inside wired as 120V from the factory. I'll be using an isolation transformer to make 240V. Then, I run a fuel economy test to see how many kWh we can add to my solar battery bank per gallon of diesel fuel.