T H E R E ' S NO DOUBT THAT

preventive maintenance is the key to keeping your aircraft ready to fly while also reducing your maintenance and replacement costs. Some of aviation's

"best maintenance prac- [ubrJci tices" involve keeping your aircraft's engine properly lubricated. H e r e are s o m e o f t h e oil-related m a i n t e n a n c e areas aircraft owners often overlook, a n d some c o m m o n mistakes t h e y make when maintaining their airplane's piston engine. Oil's Well That Ends Well Viscosity--Select the right viscosity or "thickness" of oil for your engine. We often hear people say, "The heavier the engine oil, the better it

will protect my engine." Indeed, viscosity is the single most i m p o r t a n t physical p r o p e r t y of an e n g i n e oil because one of its primary functions is to separate m o v i n g m e t a l parts within the engine. H o w e v e r , t h e r e are t r a d e - o f f s w h e n choosing oil viscosity. Select-

am,

tion is .key.to keeping your piston eng,ne ,n top shape STEPHEN M. SUNSERI ing one that's too thin will result in an insufficient l u b r i c a n t film t h a t can lead to increased wear and potential metal-to-metal contact in engine parts such as journal bearings, which require h y d r o d y n a m i c lubrication (separation by lubricant film). Conversely, using oil that's too thick will result in increased fluid f r i c t i o n (or "drag") and i n c r e a s e d power requirements, b o t h of which adversely affect fuel economy. Fluid friction also causes engine parts to overheat, and increased oil temperatures can accelerate o x i d a t i o n and reduce a lubricant's life. Engine manufacturers recomm e n d oil viscosity based on an en-

gine's ambient operating temperature. Make sure y o u ' r e using the right oil viscosity for your particular engine and operating conditions. Oil C h a n g e s - - O i l is designed to get dirty. That's h o w it keeps y o u r e n g i n e clean. But this o n l y works if you change your oil w h e n you're s u p p o s e d to. If y o u r e n g i n e has full-flow filtration, you should c h a n g e y o u r oil every 50 hours or every four months, whichever comes first. W i t h o u t full-flow filtration, y o u s h o u l d c h a n g e y o u r oil every 25 hours. Because water and contaminants settle to the b o t t o m of cold oil, change your oil when it's hot. When the engine is fully warmed and then drained, a higher percentage of contaminants are removed with the oil. If you drain it when it's cold, some contaminants will remain in the oil pan and will contaminate your fresh oil. Oil Filters--Always change the oil filter w h e n you change the oil. Not changing the filter mixes a quart of dirty oil with the fresh oil you add to the engine. In addition, the first use has reduced the filter's effectiveness, and it may clog or fail during the second drain interval, leaving your engine unprotected. Oil Temperature--Maintain oil t e m p e r a t u r e in the range of 180 F to 185°F during flight. This tempera t u r e r a n g e boils a w a y m o i s t u r e t h a t has a c c u m u l a t e d in t h e oil. W h e n y o u r a i r c r a f t sits o n t h e ground, the a m b i e n t t e m p e r a t u r e heats t h e e n g i n e d u r i n g t h e day. W h e n it cools at night, water vapor in the e n g i n e condenses, creating m o i s t u r e t h a t can, of course, lead to rust on engine components. Oil t e m p e r a t u r e s t h a t are " i n the green" are n o t necessarily h o t e n o u g h to boil away moisture, so c h e c k y o u r gauge for a c c u r a c y b y placing the probe in boiling water. If y o u r oil t e m p e r a t u r e gauge has n u m b e r s , it s h o u l d read a p p r o x i m a t e l y 212°F. If y o u r gauge doesn ' t h a v e n u m b e r s , m a r k it w i t h a reference line during y o u r temperature check. Sport Aviation

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Building Basics High temperatures are a concern in turbocharged engines, and peak temperatures can o f t e n be 70°F h i g h e r than oil sump temperatures (the temperature showing on your gauge). If your oil temp is significantly above 180 ° F, check the cowling's baffles to make sure the cylinders are getting a good flow of cooling air. Also keep an eye on CHT, EGT, and lean your en-

gine appropriately. Oil C o n s u m p t i o n m S o m e oil cons u m p t i o n is g o o d b e c a u s e it indicates that your oil is providing a seal at t h e c o m p r e s s i o n ring. Low oil consumption may indicate that sealing is inadequate, leading to blowby, p o w e r loss, a n d i n c r e a s e d c y l i n d e r b o r e wear. So w h a t ' s t h e right amount? If your oil consump-

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JANUARY 2002

t i o n exceeds the limits d e f i n e d b y the m a n u f a c t u r e r (this is the n u m b e r t h a t h e l p s d e t e r m i n e if y o u r rings h a v e sealed d u r i n g r u n - i n ) , then it's too high, and you may have a problem with an unseated or broken ring. For all Textron Lycoming engines you can calculate the maximum limit with this: 0.006 x BHP x 4 + 7.4 = quarts per h o u r Expressed differently, 0.003 quarts per BHP/hour (multiply 0.003 times your horsepower to get oil consumption in quarts per hour). Again, this is the m a x i m u m rate of oil consumption allowable during r u n - i n , a n d it averages a b o u t o n e quart per hour. Following break-in, oil c o n s u m p t i o n should stabilize a t some lower rate. The lower limit is more difficult to establish because there are m a n y variables affecting oil consumption. In the early 1980s, the University of Illinois followed 12 engines through TBO and established average rates of 0.081 q u a r t s p e r h o u r a n d 0.095 quarts per h o u r using multi-grade and single-grade oils, respectively. Unless there is a problem, your oil c o n s u m p t i o n s h o u l d stabilize and r e m a i n s o m e w h e r e in the range of between 0.08 quarts per hour on the low e n d a n d t h e oil c o n s u m p t i o n test limit as defined by the m a n u f a c turer on the high end. Oil A n a l y s i s m I f c h a n g i n g y o u r oil regularly is the most cost-effective insurance you can buy for your engine, then oil analysis is certainly the most cost-effective rider you can add to this policy. As an aircraft engine oil does its job, its composit i o n changes. It a c c u m u l a t e s cont a m i n a n t s , s u c h as c o m b u s t i o n b y p r o d u c t s , dirt, c o r r o s i o n particles, a n d m e t a l l i c w e a r particles, w h i c h can i m p a i r l u b r i c a t i o n and accelerate wear. Analyzing the cont e n t of this used oil can h e l p y o u discover engine problems before they cause engine failures. The best

p a r t is t h a t oil analysis costs o n l y pennies per flight hour. You can e n h a n c e the accuracy of this analysis several ways. First, take samples properly. Filling the sample container midway through your drain gives you a representative sample, not one loaded with all the dirt on the b o t t o m of the pan. As stated previously, always drain engine oil when it is hot. Second, change your oil and take y o u r s a m p l e s at c o n s i s t e n t i n t e r vals. Finally, d o n ' t rely o n t h e results of a single sample. Unless s o m e t h i n g is d r a s t i c a l l y w r o n g , trends take time to develop. Trends e s t a b l i s h e d o v e r five to 10 d r a i n s are m u c h m o r e r e p r e s e n t a t i v e of w h a t m a y be g o i n g o n in y o u r engine t h a n any single sample. Additives If y o u ' v e p u r c h a s e d top quality e n g i n e oil (SAE J1899), y o u d o n ' t n e e d oil a d d i t i v e s a n d o t h e r p r o d u c t s in y o u r crankcase. T h e m a n u f a c t u r e r of y o u r oil h a s d o n e all t h e w o r k necessary to ensure t h a t y o u r oil will p e r f o r m the necessary functions y o u r engine requires of it. The notable exception, of course, is the L y c o m l n g additive LW-16702, an a n t i - s c u f f i n g / a n t i wear additive required for some Lyc o m i n g engines (O-320-H, O-360-E, LO-360-E, T O - 3 6 0 - E , LTO-360-E, TIO, and TIGO-541).

Automotive Oil Unless specifically r e c o m m e n d e d b y the e n g i n e manufacturer, using a u t o m o t i v e oil in your engine is, at best, a questionable m a i n t e n a n c e practice, and one certainly not authorized by the FAA. Until the early 1940s, most engine oils were straight mineral oils wlthout additives. In the late 1940s, to improve an oil's resistance to deposit formation, the industry adopted additive t e c h n o l o g y that was working well in automotive engines specifically the use of detergents containing calcium, barium, and zinc. The results for aircraft engines, as y o u p r o b a b l y guessed, were disastrous. These additives f o r m e d 1nor-

g a n l c d e p o s i t s in t h e c o m b u s t i o n c h a m b e r that caused problems with pre-lgnitlon--not the harmless ping-ping-ping y o u sometimes hear in your car, but destructive pre-lgnltion. Automotive oils contain some of t h o s e s a m e additives today. Uslng t h e m can lead to ash deposits in an a i r c r a f t e n g i n e ' s c o m b u s t i o n

c h a m b e r and cause potential pre-lgnitlon problems, c..~-.

Steve Sunseri is tile general aviation industry m a n a g e r m A m e r i c a s for ExxonMobil Lubricants & Petroleum Specialties Company. He's based in Richmond, Virginia, and can be reached at [email protected].

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