The problem with straight grade aviation engine oils is that the correct viscosity grade for a normal operating temperature is often too viscous to flow easily at start up, and the correct viscosity grade for easy flow at start up is not thick enough at normal operating temperatures. It also affects the oil’s ability to circulate quickly throughout an engine during start up. It is the single most important property of any lubricant as viscosity influences the oil’s ability to keep moving metal surfaces separated during high and low temperature operation. Viscosity is the measure of a fluid’s resistance to flow. The key differences between “straight grade” and “multi-viscosity” oils Plus, over road engine oils contain cleanliness additives that are not present in aviation oils. Mineral oils with a greater solvency provide for a much cleaner engine with better heat transfer, better combustion control, and less sludge and carbon.įull and semi-synthetic oils are proven to be effective in car and truck engines, but the over road engine oils are not exposed to the lead byproducts associated with the use of avgas containing tetraethyl lead (TEL). The greater solvency eliminates the accumulation of lead byproducts and keeps contaminants in suspension, allowing these contaminants and lead byproducts to be removed from the engine during the oil change. This advantage is associated with the superior solvency of mineral versus a semi-synthetic oil. The four-month limit removes water which can condense within an engine during periods of inactivity and from not achieving an engine oil operating temperature around 180 F.Īs recognized by various engine rebuilders, there is a distinct advantage associated with the use of a 100 percentmineral oil (such as Phillips 66 X/C Aviation Oil) versus semi-synthetic aviation engine oils. For many general aviation engines that are flown infrequently and operated 50 or less hours per year, the four-month limit is a more important criteria than the 25- or 50-hour limit. Since contaminants accumulate during engine operation, certified engine manufacturers recommend that oil should be changed every 25 operating hours in an engine not using an oil filter, and 50 hours when an oil filter is used, or in either situation every four months. Engine oil contaminants originate from several places, including combustion blow by (raw fuel + exhaust gases), lead byproducts from the use of avgas, outside air ingestion associated with the engine air induction system, and engine wear particles.
#AVIATION MINERAL OIL VISCOSITY FREE#
For maximum engine life, this thin film of lubricant must be clean and free of contaminants. Engines depend on a thin film of oil to eliminate sliding friction and wear associated with metal-to-metal contact between moving engine surfaces.
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