The WVO and Diesel will not seperate, in the tank or otherwise, unless you are using Hydrogenated (shortening) oils. It has to be the kind that is liquid, even at 35 degrees. However, the 50/50 mix is still too thick to run especially below about 80 degrees and even more especially in the newer electronic injector engines. However, on a simple engine (IDI), a simple heated fuel filter running off your heater hose makes a great alternative to big time mods, as long as it stays abovo 60 outside.