Most sensible people who run on veg oil use a twin tank system , (on road vehicles anyway) ,the second tank is usually installed in the boot ,one tank contains diesel the other tank contains veg oil ,through a series of solenoids and console mounted switches ,the engine is started on diesel and run up to operating temperature ,then the diesel is switched OFF and the veg oil switched ON ,as the engine is warm ,the veg oil thins as it passes through the fuel lines putting less stress on the fuel system components ,towards the end of the journey the veg oil is switched OFF and the diesel switched ON ,by doing this it purges the fuel system of any veg oil ,you can add veg oil directly to diesel and it will mix ,BUT veg oil has a far higher gel point than diesel and can clog up fuel systems during cold weather ,using veg oil that's been converted into BIODIESEL ,can be added just as you would do normal diesel without any complicated engine/fuel system modifications ,using the correct additives , biodiesel can be run all year round ,even in the harshest winter
until it all gels up in winter