Oil is often considered the lifeblood of machinery. To keep equipment in peak condition, effective oils must multi-task in order to fulfil many different roles. For instance, an oil must lubricate moving parts allowing them to not only move freely but ensure that they do not grind together causing wear. Oils also serve as a coolant, reducing heat in working areas and transferring it to avoid damage. Oils must deliver other types of protection by sealing parts against corrosive forces such as rust. As oil pumps through a system, it also acts as a cleaner and carries out impurities and contaminants to ensure innerworkings never become clogged.
While many different automotive vehicles can run on regular oil, the engines installed in aviation transport require more specialist formulations. In this blog, we’ll examine the difference between oils used in aviation and regular oils. However, first we must consider the engines they serve.
Understanding the differences between aviation and automotive engines
Engines fitted in cars, coaches, trucks, and other automotive vehicles are cooled by water, while aviation engines are mostly air cooled by necessity, to reduce the overall weight of the aircraft. Air-cooled engines rely on oil to migrate heat from the cylinders and to the cylinder head, or to a dedicated oil cooler to manage excess heat. A temperature difference of up to 300 degrees can exist between the cylinder base to the oil-cooled cylinder head within an aircraft’s engine. As a result, aircraft engines must have large clearances that can withstand extreme temperature ranges and enable oil to pass through cylinders and burn.
Automotive engines are water-cooled and involve heat being carried away via a coolant system. This enables enhanced temperature regulation and even tighter tolerances inside the engine to reduce the likelihood of oils burning. While the oil employed in this engine type aids in cooling by carrying away heat, its main function is always to lubricate.
Aircraft engines are prone to activity called shock cooling. This occurs when aircraft are approaching land and descending from being at cruising altitude. The vehicle is throttled back, generating less heat from its engine but increasing airspeed, which causes the engine to rapidly cool down. Swift and sudden reduction in temperature can result in cylinder heads cracking but through the use of oil cooled cylinder heads, this issue can be dramatically reduced. The still-warm oil passes through the cylinder heads, slowing how fast the temperature decreases within the cylinder head.
The difference between aviation and regular oil
The engines designed for aviation were created before lubrication manufacturers started adding ashless dispersants to the oil, and their design has not altered much over time. Ashless dispersants can help inhibit the build-up of metallic ash and effectively disperse contaminants, ensuring they are suspended in the lubricating oil, stopping them from amalgamating and becoming sludge. These contaminants can then be passed harmlessly through an engine’s oil filter and efficiently extracted from the oil. The advantages of utilising ashless dispersants were first recognised in automotive engine oils and then considered for use in the field of aviation.
The core difference between aviation engine oil and regular engine oil is a question of additives. The difference between aviation and automotive oil began with the inclusion of zinc anti-wear additives and detergent additives that contained metal. These additives did not work well in a high-heat environment such as that found in the air-cooled piston engines of aircrafts.
As mentioned earlier, these engine types burn a considerable amount of oil, and anti-wear and detergent additives containing metals can cause metallic ash deposits to form in the engine’s combustion chamber. This can lead to hazards like pre-ignition in the chamber which burns holes in the piston heads. When cruising at 15,000 feet, the results would be catastrophic. As a result, most aviation oils today are mainly ashless.
Although specific additive packages are now considered extremely beneficial for automotive engine oils which use zinc for its anti-wear properties, they should never be added to aviation oil. Today, there are carefully formulated additives with no ash, that are specifically designed for use in aircraft oil. Though the aim of the additive is identical, the chemical composition is completely different.
Finally, another key difference between aviation oils and regular oil is price. The cost of ashless lubricants containing no metal designed for aircraft engines can be as much as 10 times higher compared to regular engine oils.
While those looking to reduce their bottom line will always seek out affordable alternatives, the cost of using an incorrect lubricant in an aircraft engine will outweigh any savings. From increased maintenance due to damaged engine parts to total mechanical failure leading to loss of live and financial investment, the risks of using improper oil are never worth taking. Before selecting an aviation oil for your fleet, always examine your OEM specifications to be safe.