Fuel efficient car?

Question

what do you have to do to make your car run on vegi oil?

Answer 1

Plant a cornstock in the block

Answer 2

You have to have a diesel, and to run on straight vegetable oil you need to make a conversion to the engine.  A discussion is linked below.

Answer 3

Only a diesel engine will run on vegetable oil processed into biodiesel fuel, and no diesel smaller than those used ships will run on straight filtered vegetable oil.  

Food-based fuels are not a very practical proposition.