This is what it says in my VW Jetta diesel manual...Mind you it is an '85...
"If winterized Diesel No.2 is not available, mix Diesel Fuel No.2 with up to 50% Diesel Fuel No.1 or Kerosene. Engine power may drop. Therefore keep percentages of No.1 Diesel Fuel or Kerosene as low as temperature allows.
Only if Diesel Fuel No.1 nor winterized Diesel Fuel No.2 are available, use up to 30% leaded or unleaded gasoline.
Do not use Premium gasoline
Mixing Diesel Fuel No.2 with No.1 with Kerosene or gasoline, must be done before wax starts to seperate. Later mixing may be effective in the fuel tank but not the rest of the system.
Always add the correct amount of No.1, Kerosene or gasoline to the fuel tank first, and then fill up with Diesel fuel No.2.