There is always much discussion about what oil to use in radial engines. Some people say to use straight mineral oil for break in. Then switch to an AD oil. Others say to use the mineral oil forever. I prefer to use an oil designed specifically for radial engines. It’s Phillips 25w60. You can use it for break in and then for the life of the engine. Mineral oil is a good choice but just understand that it does not keep particulates and contaminates in suspension. It deposits the gunk in the corners and crevices of the engine. It won’t carry them to a filter. An AD oil, on the other hand, carries all that garbage to the filter and the AD components Help keep the inside of the engine clean. One caution….if you have hundreds of hours on mineral oil and then switch to an AD oil, be advised that there is going to be a lot of gunk in your filter. Not a bad idea to change oil and filter more often until the engine gets cleansed out. Also, the 25w60 is multi-viscosity so can handle higher and lower temps better than the straight 100 mineral oil.