In World War II it was common practice to dilute the engine oil of aircraft that were operated in Arctic conditions by adding gasoline to the oil. In fact many of those big radials could not be started in extreme cold conditions if the oil had not been properly diluted with gasoline. However, it needs to be noted that those aircraft had a huge oil tank that continuously added oil to the engine to make up for loss, which was considerable. Therefore, after a while of running the majority of the initial oil that had been diluted would have been burned out of the engine and replaced with oil from makeup supply, which although I have no actual data about, probably was not diluted or at least not as heavily diluted. Keep in mind that they did not have multi-grade oils back then.
Years ago an elderly gentleman who was an aircraft mechanic during World War II told me about how they used to dilute the oil with gasoline on those aircraft. He also told me that for the Corsairs they used to shim the wing where it met the body to adjust the angle of attack of the wing with respect to the rest of the aircraft to get the aircraft to be able to fly at a higher rate of speed than it would be able to initially fly without that shimming, but that's an off topic subject. If I remember correctly, I think we actually said was they adjusted the angle of Attack Of The Wing by removing some of the shims that were on the back part of the wing.