Everything about Mobil AV-1 was wonderful except the 200 hour oil change interval. It seems that synthetics have no more ability to suspend lead that any other oil and when the lead settles out problems start. The oil was particularly important to operators of turbocharged engines which are very
hard on the oil. Interestingly Mobil did not ask for the 200 hour interval, the FAA gave them that time based on testing performed at flight schools which put a lot of time on engines very quickly. The world of aviation oils would be very different today if the oil had been changed at 50 hours. The other side of your position is that the small Continentals will make 2000 hours TBO on conventional straight weight oils. The problems they suffer seem to be in the cylinder head and valve areas and do not seem to be related to oil failure. So how much of a test pilot do you need to be. The FAA approved oils work acceptably well and are well known in the aviation world. I am paying $2.00/qt for aviation oil and changing it every 20-25 hours. I don't question the value of synthetic oil and certainly there would be little turbine flight without it but conventional oil is good enough and I save 'test pilot' for other things. A mechanic I talked to about installing the El Reno filter pointed out to me that the engines were reaching 2000 hours without it and that frequent oil changes were the best thing that could be done for an engine. A little side story - Caterpillar built a natural gas fired stationary engine used to run a generator in a remote location. Because the engine was going to be running unattended and because natural gas is a very clean fuel they made a special effort to build a well sealed engine which neither leaked nor consumed oil. Contrary to expectations the engine had a very short life. It turns out that although the oil remained slippery, the additives are consumed and in normal engines replaced with the oil normally added. Without the additives the engine corroded while it was running. Bob Condon
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