Q: There was a company that made engine pre-oilers. This would be the perfect component to add to an aircraft engine, wouldn’t it? You could go out to your hangar and turn on the pump, circulating oil over all those areas that suffer from corrosion. Why aren’t these more popular?
A: Rolf, you’ve raised an interesting question and I am probably opening a can of worms by answering it.
Engine pre-oilers have been around for many years and, if I’m remembering correctly, they were very commonplace during the big radial engine days.
It really depends on whether you are buying or selling them as to their usefulness and it’s at this point I could get myself in trouble.
I’ll share with you my personal thoughts. There is no doubt they serve the engine well when it comes to getting oil to certain areas of the engine.
However, the pre-oilers I am aware of do nothing to provide oil to the most critical areas, especially when it comes to corrosion, such as the interface between the camshaft lobe and the tappet body face, and the cylinder walls.
While these areas are the most critical when it comes to potential corrosion, they have no pressure oil feeds like the main, connecting rod, and camshaft bearings have. The corrosion prone areas I’ve mentioned are only lubricated with splash oil after the engine is started.
This raises the question as to whether the pre-oilers really serve the purpose we think they should.
While they certainly don’t cause any problems in the engine, they are incapable of doing what we’d like them to do, which is provide oil to those areas where we know there are serious issues, especially if an aircraft has extended periods of inactivity.
The best method to prevent corrosion in your engine is to fly it frequently for long enough to get the oil temperature up to at least 180°F for a half hour before landing.
Under no circumstances should you just ground run the aircraft. That is not a substitute for flying and, in fact, adds insult to injury by generating more condensation in the engine, which leads to corrosion.
Also important is to do frequent oil and filter changes (25 hours with a pressure screen or 50 hours with a full flow filter) and go no more than four calendar months.
The issue is not the lubricating factor of the engine oils, but rather getting all of the contaminates from combustion and condensation out of the engine. Those are what accelerate corrosion. By following an oil change schedule you can keep corrosion from getting its foot in the door.
Remember engine oil is one of the least expensive things you can put in your engine.