Engine maintenance is crucial for optimal performance. An engine thrives on three things: clean oil, clean fuel, and clean air. While we filter and monitor the oil and fuel, the air requires more attention. Engine washing, when the engine needs cleaner air, can work wonders in maintaining its health and efficiency.
A clean engine is a happy engine. Pratt & Whitney Canada’s maintenance manual provides insight into types of engine washes, guidelines for washing and why they are important. However, the maintenance manual does not explicitly tell us when to wash. How often do you wash your PT6 engine?
It is time to discuss the types of engine washes that you should be doing and my thoughts on how often you might do each type. If you have sat through an engine discussion, washing almost always comes up as a topic of conversation. The maintenance manual defines three internal types of washes: Desalinization, Power Recovery and Turbine. I also remind folks to pay attention to the external engine wash. Not only does it give you a chance to look your engine over, but it also provides an opportunity to make sure you have cables and components lubricated. Not cleaning these components and caring for their proper lubrication can lead to premature wear and failure. You want to be looking for early signs of corrosion as well. The earlier you catch corrosion, the better. I have had several discussions lately troubleshooting worn or parts being affected by the operating conditions (corrosive environment).
All internal engine washes are performed while the engine is running. This process provides two additional things to watch out for: first, ensure that you do not overheat your starter/generator and allow for proper cooling between motoring cycles. The second concern is the potential to siphon the oil from the oil tank and flood the accessory gearbox, which is more common in large PT6 engines. An indicator of this is oil coming out of the inlet case. When washing a large PT6 engine, we aim to do as few motoring cycles as possible.
Begin your internal washes by engaging your starter. When the Ng is between 10% to 25%, the water or cleaning fluid is injected into the engine at a rate of 2 to 3 gal/minute. Make sure to read your maintenance manual to see the complete washing instructions. All internal engine washes are performed while the engine is turning. Let’s define the wash so you can make the best choice as to what type of wash you need.
The first internal wash is the desalinization wash. This wash is performed to remove salts, deposits and light dirt. This wash is performed with drinking-quality water, provided minimum standards are met. People who live in areas with a high mineral content in the water should use demineralized water. Desalinization wash can be a daily or weekly wash, depending on the atmosphere in which you fly. We talk about salt air, pollution, dust, and sand, but what about corrosive products delivered with ag aircraft? Can these materials make it through the air filtration? I suggest checking the cleanliness of your compressor during your 100-hour inspection. This check will let you know if you need to increase the frequency of your desalinization (plain water) washes. If you are doing a lot of fertilizer, run some water through your engine. Some chemicals quickly cause corrosion on and in the engine when not taken care of.
The second internal wash is the performance recovery wash. Pratt & Whitney Canada recommends this level of washing if there is a noticeable difference in engine performance. If you are doing regular desalinization washes and the compressor still shows signs of dirt/salt/chemicals, add a performance recovery wash to your regular schedule. This wash is like the desalination wash with the addition of a cleaning solution. Important note: ONLY use approved chemicals in the cleaning solution. Several options are available, listed in the engine maintenance manual, along with the proper mix ratios. Don’t put non-approved chemicals in, as this could cause even more damage than not washing.
The final internal wash is the compressor turbine desalinization wash, which is another wash that is a rinse. This wash sprays clean water directly on the compressor turbine blades. A tool is required to perform the compressor turbine desalinization wash. A water rinse of the turbine is recommended when doing a performance recovery wash as the final step. This wash removes residue from the CT blades and limits the opportunity for sulphidation to attack blade coating and parent material. You need to perform this wash if you notice dirt or other things “sticking” to your com “ressor t” rbine (CT) blades. The blades are inspected at each nozzle interval via borescope, so you will watch how they are doing. If anyone has had to replace CT blades, then you know just how valuable this small amount of preventative maintenance can be.
I encourage everyone to wash their engines based on what they see in and on them. Some customers wash daily, some weekly or every 100 hours. It is all based on condition. Make sure you reference the manual for all the proper steps. Make sure all the drains are open and draining. Make sure to disconnect the air system going to the fuel control from the engine. People should wash before the work day, giving you the best opportunity to dry the engine after the wash – an important step in the process. Cleanliness can make a world of difference not only in the performance of your engine but also in providing an opportunity to save you money as a preventative step.
Robert Craymer has worked on PT6A engines and PT6A-powered aircraft for the past three decades, including the last 25+ years at Covington Aircraft. As a licensed A&P mechanic, Robert has held every job in an engine overhaul shop and is an instructor of PT6A Maintenance and Familiarization courses for both pilots and mechanics. Robert has been elected to the NAAA board as the Allied-Propulsion Board Member. Robert can be reached at robertc@covingtonaircraft.com or 662-910-9899. Visit us at covingtonaircraft.com.
