Adding three ounces of oil to a gallon increases the total percentage by a bit over 2%. 1 ounce increases it less than 1%. Both of these are negligible amounts. I fly in the winter and it gets cold up here. I use nothing but 20% castor fuel. Temperature makes no difference in the consistency of the fuel. I have put fuel in the freezer at zero degree overnight and it is still nice and "watery" with no thickening.

The amount of oil that gets on a plane after a ten minute flight isn't really all that much. After a days flying all it takes to clean it off is a couple of paper towels and a few squirts of 409. Think about this 20% of 8 ounces is 1.2 ounces and of that amount, very little ends up on the airplane.

Now I will say this. In the winter when it's cold, the oil that does end up on the plane is thicker and a bit more difficult to clean off but not enough to traumatize anyone.