Hi need some help. I need to know how many ml. of castor oil to add to one U.S. gallon of fuel to up the lube from 18% to 20%. I can pull off the math with consideration for total volume only, but I don’t know if I need to consider nitro (10%) and oil (18%) content. Thanks for your help.

You will need to add 2.56oz of oil to get 20%.

thank you

To raise the percent oil from 18% to 20%, add 3.2 oz of oil, not 2.56 oz, to a gallon of fuel. 3.2 oz is about 95 ml. What you will end up with is 131.2 oz of fuel that has 20% oil and 9.76% nitro. If you want to end up with fuel that has 20% oil and 10% nitro, you will have to add 3.29 oz of oil and .37 oz of nitro. If you search this forum, you can find links to websites that have calculators that will do this calculation for you.

thank you for the further info. I figured about 3.1-3.2 for total volume but seeing the first number in the replies thought it was to compensate for nitro and existing oil. Don't know why I care this much. The plane is still going to make a smoking hole in the ground. Suppose I can rest assured knowing the engine is going to run good all the way down.

"The plane is still going to make a smoking hole in the ground. Suppose I can rest assured knowing the engine is going to run good all the way down."
I know the feeling. I can honestly say that I have never worn out an engine, but I hope to someday!