All internal combustion engines suffer from four basic problems; corrosion, wear, sludge/carbon, and dry leaking seals. Additives can address all four of these issues, but the chemical combinations can get complicated. A number of chemicals are available to address all of these problems, however caution must be used. Some additives can convert to harmful chemicals, even acids, as an engine operates. Different molecules within the chemicals are attracted to other molecules, whether in the oil or in the metals of the engine. The additive designer has to know all of the qualities and how to best combine the components to create an additive that provides the benefits while having no harmful effects.
To better understand oil additives one must first understand oil, lubrication, and the fact that almost every type of oil has some sort of additive. Today there are two types of oil generally used in reciprocating aircraft engines: mineral oil which is a basic petroleum stock, and synthetic/semi-synthetic oil.
Let’s begin by looking at the nature of oil and the chemistry of an additive package at the molecular level. Oil carries heat to a cooler or back to the sump. Oil's primary cooling job is to splash onto the bottom side of the piston, cooling it and keeping it from melting. It then runs into the case and sump. Secondly, it provides two types of lubrication. Under pressure it creates an oil wedge, and fills the spaces between metal parts. This is hydrodynamic lubrication and is dependent upon oil movement through the parts. It also provides boundary lubrication where there is definite metal to metal contact, like the cam lobe/lifter face. Thirdly, oil works to contain combustion gases in the cylinder and works with elastomeric seals on any rotating shaft to seal the case. Finally, oil carries sediments and impurities which are either filtered out or carried in suspension.
To do anything else oil must contain certain additives. The science of additives is real and technical, and when used in the proper combinations and ratios with oil they produce remarkable effects. Additive packages are designed to perform certain tasks and are the most expensive component of a quart of oil. We all want the same thing in our aircraft engines, so the goals are pretty cut and dried. There is a difference, however, in what chemicals can or should be used to achieve desired results.
For operational flexibility, the handiest additive ever developed is the Viscosity Modifier (VM). This gives us the ability to operate in different parts of the country or to fly through seasons with different temperatures. The VM is a star shape molecule. When cold these clench up like a fist, and as the oil heats they relax, open up and begin reacting with each other, preventing it from thinning out as its temperatures rise. Multi-viscosity oils will always allow easier engine startup and faster oil pressure.
According to Ed Kollin, a formulation chemist who focuses on high performance lubricants, the best AD base oils out there are Shell 80 and 100 straight weights, and for multi-viscosity, Phillips 20-50 XC. These are also the most economical as there are no up-charges for additives.
Engine operation does cause problems
Corrosion in an engine is primarily caused by water combined with acids in the oil. Water is a by-product of the combustion process, creating a gallon of water per gallon of fuel burned. Most of this water is blown out the exhaust, but some gets past the rings and into the crankcase where it is churned into the oil. As oil cools, it expels the water, which is attracted to metal parts. Additives can prevent water and acids suspended in the oil from contacting a metal surface by creating an impermeable, one molecule thick film over the inside surfaces of an engine as soon as oil flow stops until the flow starts again.
Wear is addressed by a sacrificial film forming molecule. Cam lobe/tappet contact produces up to 125,000 psi. This pressure causes frictional heating and converts the molecule into a film, preventing contact at startup and while running.
Deposits and sludge both start with varnish (like in the can) that is formed from partially burned blow-by fuel. Once the dispersant is used up, this varnish polymerizes (crosslinks with its neighbors) and paints the inside of the engine. Sludge is that grey goop that forms in an engine. It is a combination of sticky varnish and lead particles from the fuel and settles in areas of the engine where there is little oil flow. We see sludge affecting the oil control rings resulting in higher oil consumption. This issue is particularly seen on high-power small-sump engines operating with 6 quarts of oil in the engine. Additives can contain components that stop the chemical reaction that forms the sticky varnish, preventing both varnish/carbon films and sludge from forming.
Seals deteriorate over time because of heat and age. The stain or film around a push rod tube cover, or weeping around a seam can be eliminated by using certain additives which contain specific components to condition/recondition any seal it touches, keeping it flexible as if new. The result is a much cleaner engine compartment.
Additives
Traditionally, additives have been marketed rather flamboyantly with a lot of promises, and have created equal numbers of devotees and skeptics. Many would ask, are they snake oil or elixir? One of two FAA accepted oil additives, CamGuard, was developed in a partnership between Greg Merrell with Aircraft Specialties Services, and Ed Kollin, a formulation chemist who’s focused on high performance lubricants. Tested in a high performance airshow aircraft and accepted by the FAA in 2006, Kollin designed this additive package for use with any good base oil at a ratio of 1.6 ounce/quart, at oil change or when top off oil is added. Any additive can be added to the more expensive fortified oils (Elite/-Plus, etc.), however, it may not be economical.
CamGuard uses chemistry to prevent the four problems, using 11 chemical components. It is designed to prevent any water and acids suspended in the oil from contacting a metal surface by creating an impermeable, one molecule thick film over all inside surfaces as soon as oil flow stops. It remains in place until the flow starts again. The formula contains components that stop the chemical reaction that forms the sticky varnish, preventing both varnish/carbon films and sludge from forming, and it contains specific components to condition/recondition any seal it touches, keeping it flexible as if new. The result is a much cleaner engine compartment.
There is a definite economy that goes with adding oil additives to engine oil seen in lower maintenance and overhaul costs and every time you add oil. But, for the aircraft owner, knowing what is going in an engine creates a peace of mind that is intangible.
For more information visit www.aslcamguard.com or www.aircraft-specialties.com.
Jim Cavanagh is an aviation writer with three books and thousands of articles to his credit. He is a dedicated Sport flying pilot, winner of a number of Air Races in his highly modified American Yankee, and has built homebuilt airplanes and rebuilt a number of certified aircraft. If there is a subject in aviation, he has written about it. He can be reached at [email protected].
