Thanks for the articles Phil. They articulated very well the points that I was making about using multi-viscosity oils. The netters have already spoken at large about how the aviation oils 100w Aeroshell and the like are too thick for our engines (auto conversion guys). O-200's have it. It is designed for you, and you should run it. Auto engine guys, look at the temps you will be running and then match the multi-viscosity oil to that environment temp range the same way you would for your car. You would not run 20w50 during the winter in Wisconsin, so if you are an auto conversion guy running up North during the winter, run 5w30, or 10w30. Remember, it is getting colder as you climb, and not all of your engine has the benefit of the combustion chamber heat. In Phil's case, his PSRU gear drive will be sharing his engine oil, so it is even more critical to match the oil properly to the engine use and temp range, due to the oil shearing that the gears will cause the oil to be subjected to, much the same way my Yamaha transmission does to the engine/transmission oil (both drivetrain parts use the same oil reservoir).
By the same token a pilot in TN should not run straight 40w or 50w even during the summer, because he can have temps as low as 35 to 40 degrees in the Spring or early Fall and would need a thinner oil to insure that oil began circulating at startup to prevent early engine wear or even premature failure. Even in Florida I would be hard pressed to run 20w50 oil in my Corvair due to the fact that my particular style of flying is alot of high altitude cruising at 6, 8 sometimes 10,000 feet. As a CFI we were always educating our students about descents from high altitude being a problem for shock cooling and cracking of cylinder heads due to temp differences, and lack of work load for air flow cooling. This can also have a negative effect on the oil circulation. To paraphrase a statement made by WW in his conversion book, to be made aware of a modern enhancement that raises safety and then neglect to use it is irresponsible. There is a reason why no Fast Lube businesses or dealerships carry straight weight oils, only auto parts houses; they really don't belong in 99% of auto engines regardless of their use. As the article says, straight weight oils are likely to have the same additives as the multi oils do, just not say so, so it is a wives tail to believe you are getting more actual oil in them than multi oils. Even the article on motorcycles needing special oil endorse the use of multi-viscosity oils engineered for that application. I use Yamaha 10w40 motorcycle oil in my 2001 Yamaha VStar 1100cc cruiser and have had flawless performance since day one, with 16,000 miles to date. When I drag raced my 1980 Chevy Monza with a 300 hp 350 cid motor, I ran 10w30 in the beginning of the season and by summer's end ran 10w40 with no failures and no oil burning, and broke it in on straight 30w for 2 hours, then it never saw straight weight again. That same engine survived a total of 3 cars to date. I will break in the Corvair with straight 30w and then it will have 10w30 to begin with for initial testing. For a tight engine it is far more important to get good circulation than high oil pressure (barring too low a pressure ). With the exception of Larry's and several other people's endorsement of Marvel Mystery Oil, I have had more complaints and outright repairs due to "additives" from the after market than good. Just good regular maintenance will outperform and outlast all additives combined. Colin N96TA
