Oil Types - Explained Some oils carry a single grade number, such as SAE-50 weight. SAE stands for Society of Automotive Engineers. The numerical value, typically in the range of 20 to 50 for aircraft piston engine oils is a relative number. Lower numbers are less viscous, higher numbers are more viscous or thicker. Less viscous oil flows better at low temperature, heavier oils provide greater protection at higher temperatures. Oils get thicker when cold and thinner w hen heated. We use heavy oils in the summer time to protect the engine, and lighter oils in the winter so that it will wi ll flow in cold temperatures, especially at startup time. Oil with more than one o ne number is called a multi-viscosity oil. It is oil to which a viscosity modifier has been added to stabilize it over a wider operating temperature. A 20W-50 grade oil acts like a 50 weight oil when it is hot and a cts like a 20 weight oil when it is cold. The "W" stands for winter, hence the oil acts like 20 weight in winter temperatures. temperatures.
Oils meeting the SAE's low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). 30 ). An oil is rated for viscosity by heating it to a specified temperature, and then the n allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by b y the length of time it takes to flow out of the hole. h ole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating
#1: What does oil do? Oil is the lifeblood lifeblood of a piston engine. In protecting engines from from the harmful effects of heat, friction, pressure, corrosion, oxidation, and contamination, contamination, oil has four basic functions:
Lubrication. Lubrication. Oil protects against excessive wear between moving parts by creating a fluid barrier that keeps parts from contacting each other. Cooling. Cooling is another major function of oil. In fact, in air-cooled air-cooled piston engines, oil contributes up to 40 percent of the cooling function. Sealing. Oil provides a seal between piston rings and cylinder walls. In doing so, it helps reduce wear, provides better compression, compression, and keeps contaminants contaminants out of the cylinders. Cleaning. The fuel/air combustion process creates many con taminants, taminants, none of o f them good for the engine. As oil travels through the engine, it collects contaminants and transports them to the filter for collection and removal.
#2: What is the difference between single-grade single-grade and multi-grade oils? "Single-grades are all mineral oil and semi-synthetic multi-grades are blends of mineral oils and syntheti s ynthetics," cs," said Harold Tucker, T ucker, lubricant lubricant technical director for Phillips 66. 66 . "Simply, multi-grades multi-grades are superior for use in all temperature ranges, especially especially colder climates. Single-grade Single-grade oils are great for warmer temperatures, but when it's cold they cannot provide the quick-flow characteristics aviation engines need at start-up. For
example, during a cold start, a 20W-50 will flow as freely as a 20-weight, 2 0-weight, yet protect as well or better than a 50-weight at operating temperatures. temperatures. One thing most technicians technicians and operators don't know is that a co ld-start ld-start is any start s tart in temperatures below 60 degrees. "Aside from that, they're basically b asically the same. And most technicians technicians don't understand that," he explained. "They have exactly the same additives and base oil, the multi-grade just has a little more polymers and some other viscosity modifiers. Another misunderstanding misunderstanding technicians technicians have is that you can't switch s witch between single- and multi-grades in mid-engine life. That's just not true. All the oils conform to the same specifications specifications so you can switch between them whenever you want to." #3: Is it true that multi-grade oils break down faster than single-grade oils? Oils don't really "break down." Many people mistakenly believe that multi-grades lose viscosity or break down. But the truth is viscosity modifiers modifiers in multi-grades multi-grades make them extremely "shear stable." The fact is, multi-grade multi-grade oils remain stable throughout the normal oil change interval and beyond. That's another reason why oil change intervals are so important. Oil that goes too far beyond the prescribed time will lose some of its ability to catch and hold contaminants, contaminants, but it will not break down. #4: Are there any operational differences between single-grade and multi-grade oils? Aside from having better performance in a wider range of temperatures, multi-grade oils offer a number of operational differences. A few are: The engine will be easier to start in a wider range of outside air temperatures. Oil pressure p ressure will stabilize faster because lubrication is quicker. Engines will warm-up faster because the oil has a better volumetric flow. Operating temperatures will be more consistent. And, oil consumption may also be lowered, because multi-grade oils provide a better cylinder-ring cylinder-ring seal. #5: What happened to totally synthetic oils? They came and went pretty fast. "What we found in our testing was that th at 100-percent 100-percent synthetics provided excellent lubrication lubrication properties," said Paul Royko, senior research engineer for AeroShell. "The problem came when the engines reached 600 to 900 hours, some began to have oil consumption control problems. What we found was the piston rings were covered with lead byproducts from the avgas." He explained that by the time they added the right blending of solvents to eliminate the build-up problem, they were adding so much mineral oil that they were effectiv e ffectively ely creating a semi-synthetic semi-synthetic oil. Because of this, the decision was made to stick with the semi-synthetic semi-synthetic formulas that were already on the market. #6: Some engines use auto-gas, what about using automotive oils? Unless the airplane has a modified car engine, simply, don't even go there. There are major structural and operational differences between automobile and aircraft engines and
they have vastly different needs in their oils. Aviation oils contain fewer additives and they differ chemically from from those used in car engines. In fact, many of the detergents detergents and anti-wear additives used in auto oils are prohibited in aviation oils because of the concerns that they may actually harm some internal metal parts and they tend to leave deposits that could lead to pre-ignition and detonation problems. problems. Also, viscosities for the two oils are quite different. Because Because of the wider operating temperatures and larger internal machine clearances, aircraft engines require much heavier oils than auto engines—SAE 50 instead of SAE 30, for example. example. Sure, you'll save money with a case of Pennzoil from Kmart, but you'll do it at the expense of the engine. #7: What are the best cases for using ashless dispersant oils? "Except for break-in, ashless dispersant (AD) oils are required for use in Continental Continental and Lycoming engines," explained Steve Sunseri, general aviation industry manager for ExxonMobil. "During break-in, non-AD non-AD oils are often, but not always recommended recommended to promote wear-in and achieve better conformation of the surfaces in contact between the cylinder liners and the piston rings." [Editor's note: The use of AD o r non-AD oils during engine break-in periods is a point of great debate even among the oil manufacturers. The best way to stay on the safe side is to contact the engine overhauler or OEM and follow their recommendations. recommendations. For the most part, AD oils work fine for break-in.] #8: Do ashless dispersant oils contain detergents? No. AD oils o ils are not the same s ame as detergent oils, which are popular in automotive products. products. While detergents will loosen and remove existing deposits, deposits, AD oils will not. Instead, they will suspend contaminants and keep them from attaching to the metal surfaces until they can be filtered or drained out. For example, if an operator runs an aircraft engine for 500 or s o hours using non-AD oil, then switches to an AD oil, the new oil will not clean off the 500 hours worth of deposits deposits that have built up inside the engine. What it will do is suspend suspend any new contaminants contaminants that haven't yet solidified to engine components. components. That's why AD oils o ils seem to discolor or darken faster than non-AD oil types. The darkening simply illustrates illustrates that the oil o il is doing it's job. #10: Are there advantages to using supplemental supplemental oil a dditives? dditives? No. In fact, except in the rarest of circumstances, aircraft piston engine manufacturers do not recommend using any supplemental additives. additives. While "approved" "approved" additives may n ot harm an engine, there is little, if any b enefit to be gained from using the additives. It's agreed that it is better to put your money toward more frequent oil changes, which is proven to be beneficial. b eneficial.
#11: What are the benefits of oil analysis a nalysis? ? A lot of experienced experienced technicians misunderstand misunderstand what oil analysis can and can't do. It's not the magic bullet that can foresee engine failures. It can be a valuable tool in a more effective long-term preventative maintenance program. Oil analysis is a good way to spot trends in metal wear, viscosity integrity, integrity, fuel dilution, and air intake system leaks, among other things. "The real value comes from being able to trend the content con tent of contaminants contaminants and wear particles suspended suspended in the oil," Sunseri Su nseri said. "But trends take time to develop, and the trend analysis is much more valid if the samples are taken at consistent intervals. Whether it's at 25 or o r 50 hours, the oil o il analysis samples samples need to be taken each time you change your oil if you are looking to get maximum advantage from the data." "For example, Embry-Riddle initially found found the piston-pin plug wear problem in its Lycoming engines using the wear metal analysis from the oil analysis program," he added. "High concentrations of aluminum in their oil o il pointed to the problem in their fleet. When combined with other clues, the analysis data helped ERAU quickly identify where the problem was." "Creating consistency consistency is key ke y to effectiv e ffectively ely trending the condition of an engine," Royko added. "Owners may try to save a couple bucks by skipping analysis for a change or two. Then when there's a spike in the next analysis they freak out. In those cases, we recommend recommend the owner o wner get another analysis as soon as possible. Sometimes if the sample sample was taken improperly, improperly, there can be some outside contaminants contaminants in the sample which will sway the readings." With that in mind: #12: What is the right way to take an oil sample for analysis? "The best way to get a good sample while minimizing the chance of outside contamination contamination is to let a quart or so drain out, then t hen use a clean container container to capture the sample from the drain flow," Tucker explained. "Hold the bottle at least six inches from the drain plug. And don't pour the sample from one container to another. Also, don't dip the container into the drain tub to get a sample, that leads to contamination and inaccurate readings. The idea is to keep the sample s ample as clean as possible."
