Four stroke fuel has less oil in it. Some four stroke engine manufacturers tell you NOT to use four stroke fuel in their engines because of this. Most four stroke engines are ringed and typically like synthetic/castor blends...heavy on the synthetic. Most two stroke engines are ABC and like the same blend but heavy on the castor, there are some exceptions. Typically four stroke fuel will have 15-18% oil and two stroke fuel will have 18-22% oil, there are some exceptions. I personally use the same fuel, 10% nitro/20% oil (mostly castor), in all of my glow engines...period! My planes are a little greasy at the end of the day...SO!...my engines are in excellent shape!

It is ALWAYS good to err on the side of a little more oil if you want the longest possible life out of your engines. Speaking of oil...don't forget an after-run oil after each day of flying either! If you use a heavy castor oiled fuel in a ringed engine this is imperative! I use Marvel Air Tool Oil...you can get a quart at a auto supply house for ~$6...cheap!