Aircraft Oil vs. Automotive Oil

Aircraft owners all know the joy of owning their own private aircraft and having the skies at their fingertips. However, aircraft owners also know the many aircraft-related fees that pile up month after month. From hangar fees to fuel and general maintenance, yearly costs can reach tens of thousands of dollars. As such, many people look for quick and easy ways to save a bit of money. This leads many aircraft owners to ask the question “can I replace aviation oil with automotive engine oil?” The simple answer is no, but this blog will go into greater detail about the differences between the two oils and why they aren’t interchangeable.

Before discussing the differences between automotive and aircraft oil, let’s look at the differences between automotive and aircraft engines. Automotive engines are water-cooled, while the majority of aircraft engines are air-cooled to keep the overall weight to a minimum. Air-cooled engines are dependent on the oil to carry heat away from the cylinder head or out to an oil cooler to help control the heat. The temperature difference between the cylinder base and cylinder here can be up to 300 degrees. This is the reason aircraft engines must have large clearances: they allow the metal within the cylinder to become distorted. By design, larger clearances allow oil to pass through the cylinder and be burned.

Adversely, water-cooled engines carry away the heat using coolant. This allows for better temperature regulation and tighter tolerances within the engine. Tighter tolerances mean the engine oil is less likely to burn. The oil used in this engine is primarily used to lubricate, though it does slightly aid in carrying heat away from the engine. Air-cooled aircraft engines are prone to shock cooling, which occurs when an aircraft is approaching landing. The aircraft is throttled back, producing less engine heat, but gaining airspeed, rapidly cooling the engine. This can cause cylinder heads to crack, but oil-cooled cylinder heads have drastically reduced this problem. The oil passing through the cylinder remains warm, slowing the temperature decrease.

Now let’s look at the difference between automotive and aircraft oil. Aircraft engines were designed before ashless dispersants were being added to aircraft oil. These dispersants help slow the formation of metallic ash and prevent contaminants from clumping together and forming sludge. The contaminants are then passed through a filter and removed from the oil. 

The main difference between aircraft and automotive oil is the additives. The split between automotive and aviation oil occurred with the addition of zinc anti-wear and detergents containing metal to automotive oil. These metal additives are not suited to the high heat environment of air-cooled piston engines. As stated, this type of engine burns a large amount of oil, and any detergents containing metals and anti-wear compounds like zinc can form metallic ash deposits in the combustion chamber. This can lead to premature ignition within the chamber and ultimately burn holes in the tops of pistons. This is the main reason why aviation oils do not contain ash.

Once again, while it may be tempting to save a buck or two by using automotive oil in your aircraft, it will only cost you more in the long run. To further ensure the continued reliability of your aircraft, be sure you are getting parts from a trusted source like Unlimited Purchasing.

Unlimited Purchasing is an online distributor of aircraft spare parts, aircraft overhaul parts, and much more for a broad scope of military and civilian aircraft applications. Owned and operated by ASAP Semiconductor, we can help you find all types of unique parts for the aerospace, civil aviation, and defense industries. Our dedicated account managers are standing by and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at sales@unlimitedpurchasing.com or call us at 1-434-321-4470.


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