I’ve received several questions recently about oil filters. Specifically, if you own an aircraft that came from the factory without an oil filter, should you install an aftermarket filter?
The questions were usually divided into two parts. First, will the installation of an oil filter pay for itself? And will an oil filter increase the life or increase the chance of reaching TBO on an aircraft engine?
The question of cost is relatively simple. If you fly 150 hours a year, you will save the cost of roughly three oil changes a year.
However, you do need to increase the cost estimate for each oil change by the cost of an oil filter element. The more you fly each year, the more you will save.
The benefit for the engine question is a little more cloudy.
Common sense tells us that an oil filter that removes particles from the oil has got to be a good thing. And that is basically true.
However, there is one concern here, and that is low usage aircraft.
The idea that you change the oil every 50 hours on an oil filter equipped aircraft and 25 hours on an aircraft without an oil filter is very ingrained in the aviation community. So if you fly only 75 hours or less a year, you will be changing the oil about three times a year.
If you think that if you install an oil filter on this aircraft, you can go to 50 hours between oil changes, that may cause a problem.
Changing the oil once every year or so will probably cause problems in the long run. If the low usage aircraft sits for extended periods of time, especially in a humid climate, rust will form on many surfaces like the cam and lifters.
Then when the engine is started, this rust rouge will be absorbed by the oil and act as a lapping compound for high load wear parts in the engine. A filter will reduce the amount of this rouge, but will not remove all of it.
The bottom line here is that if you fly less than, say, 50 to 75 hours a year, changing the oil every 25 hours or a minimum of three times a year will probably give you a better chance of reaching full TBO than installing an oil filter and changing every 50 hours.
People need to remember that changing the oil at least every four months is probably the number one secret to getting to full TBO. On high usage aircraft, the 50 hours with a filter then comes into play.
So is an oil filter worth the cost? It does offer advantages for higher usage aircraft.
Another reason for an oil filter is it is probably one of the best diagnostic tools for your engine.
Whenever you change the oil, you need to cut the filter apart and look for metal in the pleats of the paper. If you do this at each oil change, you should be able to note any significant increase in metal production from your engine. This is an excellent predictor of problems before they become major problems.
As always, the basics are the most important. You need to change the oil every four months.
And if you fly more than 75 to 100 hours a year, then an oil filter may be something to consider.