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Oil dilution Back when I was in the Air Force in the mid fifties we used oil dilution in the great radial engines on the era so that they could be started on cold mornings. This was accomplished by using a switch on the aircrafts flight engineer’s panel. The flight engineer would hold the oil dilution switch on for a predetermined time so that aviation gasoline could be injected directly into the running radial engine crankcase. These engines were of the dry sump type and did not hold reserve oil in the crankcase but rather in an 80 gallon tank that was vented to the atmosphere. By injecting gasoline into the crankcase as the engine was being shut down the residual oil in the crankcase was diluted to a very thin consistency. If the engine was not shut down in antisapation of a cold morning start then the engine starter and all the power units on the base could not start these huge engines. Here we are talking anywhere from 3350 cubic inches on one engine to 4360 cubic inches on one engine. Dilute the engine when shut down start the next cold morning! The gasoline would evaporate eventually into the atmosphere from the vented tank. Not to worry about the potential for an explosion because the whole airplane was a potential for an explosion!!!!!
The story goes according to some of the old WW2 men that were still in the AF at this time that a mechanic over in England who was having a heck of time starting the engines on his squadrons planes in the cold damp mornings came up with the idea to pour gasoline into the crankcase after the engine was shut down and then restart and run for a couple of minutes to mix the oil and gasoline. The CO noticed that his planes had no problem at all being started in the morning so he called the Sgt. In and asked him what his secret procedure was. When the Sgt told his what he had been doing the CO hit the ceiling and had the Sgt busted. After all he told him, gasoline is very combustable! The Sgt told him it was while in the gas tank too. What was he going to do about that? No answer to that question! A couple of months later when the weather really got cold and nothing could be got up and going unless heaters were used all night on the engines he called the private back in and re-instated his rank with back pay and had him go out and instruct all the mechanics on the base to begin his oil dilution process when a cold morning was in the forecast. He was promoted and given a citation after the invasion of Normandy. This is a true story. Zane
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