How about that oil change? When did you say it was due? Oil is the life-blood of any engine and an oil change program keyed to a certain number of hours in service is critical. The length of service an operator can expect from a radial engine depends on it.
Operators frequently ask me, "How many hours should I go between oil changes?" That question has many answers. Many factors are involved. What type of spraying are you doing? What type of runway are you using? What temperature and weather conditions do you operate in? What is your aircraft's filtering capability? What about your engine's oil consumption?
I recommend oil change intervals of 35 to 50 hours. Of course, no one is going to shut down in the middle of a worm run to change oil because the 35 hour mark has been reached. A real effort, however, should be made to establish as regular a program of oil change and screen or filter checks as possible.
One hundred hour interval oil changes might be acceptable if the following conditions are met:
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If your aircraft is equipped with a dry air filter system in good condition and with one of the after market oil filter modifications.
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If you have installed a chip detector kit in the engine sump case drain.
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You have an operating cylinder head temperature system.
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Your home strip is asphalt and you rarely have to work off grass or dirt strips.
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Your temperatures during the season are fairly stable and your engine runs cool (165 to 175 degrees Fahrenheit).
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Your oil consumption is normal (1-2 quarts per hour).
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Your aircraft is not underpowered (working power settings averaging 2050 R.P.M. 30" M.P.).
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You are using the best aviation oil available.
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Your are on an oil analysis program and
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You have been using the same overhauler for years.
I personally believe that one hundred hours of ag operation is too long to go between screen and sump checks. Suppose you have all the good operating conditions described above except a good filtering system, you should consider intervals of 50 to 75 hours. If you operate off a dirt runway or do large amounts of heavy volume application, such as rice work, you should consider oil changes in the 25 to 50 hour range.
Pratt and Whitney engines are famous for dependability but they are also famous for letting an operator know ahead of time that something is wrong. Are you conscientious enough to look and listen?
I realize that oil isn't cheap, neither are a mechanics wages for oil changes, but if you balance that expense against unscheduled down time and shortened engine life, the economics of a good oil change schedule look pretty good!
What type of oil to use? As an overhauler, I prefer an ashless dispersant oil (AD). This does keep the engine cleaner throughout the run. However, I know many operators that have reached TBO on mineral oil. A rigid oil change schedule is more critical on an engine using mineral oil due to the amount of carbon these engines can generate. Collapsed oil screens are also more common on mineral oil engines.
As for the multigrades, I have only noticed one problem and that is lower oil pressure and higher oil temperature on some R-1340 engines in hot weather operation. I do not recommend any engine oil with an anti-wear additive be used in a freshly overhauled engine that has not yet seated in.
God bless ya'll and fly safe.
