Is this ground run up necessary?

When it comes to engines, we want to make sure we provide as much relatable experience to our troubleshooting as possible. An interesting point inspired this blog post when our up-and-coming pilot son did our last oil change on our Piper PA28-180 and we took an oil sample to get tested at Fluid Life.

The plane was started, the engine was ground-ran for approximately five minutes, not quite reaching 1700 RPM and then shut down. This was followed by the oil being drained and sampled and the filter was changed. This is common practice we know is done on a regular basis by pilots doing elementary maintenance on their aircraft.

Fast forward a couple of days, once we received the oil analysis, the sample data we got back indicated water present, and we know why, there was water in the sump that was not able evaporate during the ground run-up.

Normally for an engine at a cool state, you will find traces of water in the sump. These water traces need to evaporate out of the engine at a higher temperature than what it will reach during a five-minute ground run-up. The engine should be at full operation around 170 degrees Fahrenheit or (85 degrees Celsius) to achieve the evaporation. This is easily achieved by taking your plane out for a quick 45-minute flight! In our experience, it is better to take your plane out and burn off that water than simply ground running. Here is why…

When your plane was last flown, water would have been introduced into the oil from condensation and as a by-product of combustion. This small amount of acidic water will sit there until your next flight and will be evaporated with minimal issues. If the aircraft is regularly flown, this amount will not be much. But what happens when you just ground run? The engine will not reach an optimal temperature to evaporate the acidic water, so over time, this will continue to accumulate in the sump  and the next time you take the aircraft out, this larger amount of acidic water will be pushed through the aircrafts lines and into the engine, causing increased amounts of corrosion, and will eventually cause damage to the tappet bodies and destroy the bearings.

We recommend the following for private aircraft owners that do not fly regularly and are planning to leave your aircraft without flight for an extended period (winter for example).

  • Do not just ground run the plane once a month and walk away, if you do not intend to fly it’s not necessary to start up the aircraft monthly—leave it be.

  • Take your battery out

  • Drop the used oil and consider adding fresh AeroShell Oil 100 and a preservative oil like AeroShell Fluid 2XM. (please click here to see their preservation recommendations)

  • Approximately a month before you intend to go flying, drain half of the oil that has been sitting and replace it with fresh. This will remove anything that may have been sitting in the sump since you last flew. At this point, run your engine to get the new oil over the parts and ready to fly!

If you have any questions about this process, contact us!

Share this post