Keep same oil filter for one more oil change?

[rbridges]

I keep my plane running at least the bare minimum, about 1 hr every 3 weeks to keep engine lubed. Anyway, with the way things are, we are flying a lot less. I have 15 hours since my last oil change. Would it be okay to keep the same filter for the next change?  I know it keeps a small amount of the old oil, but I wasn't sure if that was significant.

[N201MKTurbo]

When I flew a lot, I used to do that all the time. I would change the filter every other oil change. I called it an express oil change. I would hook the drain hose up after I got back from a flight. I can do it through the cowl flap, and half the time I don't even burn my arm on the exhaust. I let it drain till the next flight, which was usually the next day. Unhook the hose and fill it with oil. If you let it drain over night, most of the oil will drain out of the filter. I can tell you that there is quite a bit of oil that is left in the sump unless you put the plane on jacks and tilt the nose down, or pull the suction screen. So worrying about getting it all out is crazy.

[RJBrown]

So it sounds like you are asking if at 15 hours but about 1 year should you change oil and filter. 
yes, both. 
what you are doing is making sure acids and water are removed from the lubrications system.  
So after 15 hours the oil should not be broken down. The reason for change is moisture and acids. 
My personal opinion is oil and filter every 50 hours or a maximum of one year. 
But hey, I like my vehicles to last. Oil and filters are cheap, engines are not. 
If it has been a year I want the cowling off to inspect inside anyway. 
In reality for me this means I do the oil and filter change at 6 months and have the oil changed at annual. Oil analysis with annual not mid year unless prior trends indicates or there is metal in the filter. 
Cutting open and inspecting the filter every change is a good reason to change it. 
 

[GeeBee]

Unless your engine is making metal, most the debris in an oil filter is carbon and waste deposits. Wash your filter media in solvent, let it evaporate and see what remains and you will see what I am talking about. So you change the oil, and run it across the old carbon and deposits creating more acid only faster. What is the point of changing the oil if you do that? In terms of cost, a filter is a minority part of the oil change, so why not change it?

 

[N201MKTurbo]

11 minutes ago, GeeBee said:

Unless your engine is making metal, most the debris in an oil filter is carbon and waste deposits. Wash your filter media in solvent, let it evaporate and see what remains and you will see what I am talking about. So you change the oil, and run it across the old carbon and deposits creating more acid only faster. What is the point of changing the oil if you do that? In terms of cost, a filter is a minority part of the oil change, so why not change it?

 

Because when I was using my airplane to commute to work, I didn't have time to remove the cowl and change the filter. I could fill it back up in about 5 minutes. The filter still got changed 3 or 4 times a year.

 

There is a lot more crud sitting in the sump than in a drained filter...

[A64Pilot]

You really should change oil once a quarter.

The acid comes from moisture from burning fuel and the chemicals in the fuel. mostly sulphur I believe, it’s not from carbon in the oil or filter.

Acid is I believe Oxygen, Sulphur and Hydrogen, sulphuric is I believe H2SO4 for instance, those chemicals aren’t in carbon I don’t think.

Now I’m normally against oil analysis, as people want to think it’s an engine analysis, and it’s not, it’s what it says it is, oil analysis.

‘So one of the better uses for it is determining oil condition, so take an oil analysis and specifically ask for TBN and TAN, which oddly isn’t in a normal aircraft oil analysis I don't think.

‘Anyway TBN is Total Base number, which is a measurement of the oils ability to neutralize oil, a good TBN number means the oil is still providing good acid protection.

TAN is Total Acid Number, which is exactly what it sounds like.

‘It was Diesel engines back in the day burning high sulphur fuel that really created acid, but TBN and TAN will tell the acid story of any engines oil, there are other factors of course but they don’t really come into play with little use,15 hours isn’t going to “wear” out oil.

 

But bottom line is oil is the cheapest thing about an aircraft engine, don’t be penny wise and pound foolish.

In my opinion it won’t hurt to change filters every other time, just don’t put more than 50 hours on a filter. (just an opinion)

‘A filter should have an anti drainback valve that does what it says it does, in other words draining the pan even for a week shouldn’t drain the filter. The valve exists so that at every engine start your engine gets oil pressure quickly,if it had to refill a drained filter, then it wouldn't.

If I were in your position I’d seal the intake, exhaust and crankcase vent trying to prevent moisture from entering the engine.

‘Some will put desiccant filters on the crankcase vent, and that may be a good idea. I’d want one that you could dump the desiccant and dry it out and reuse it though 

Edited March 12, 2021 by A64Pilot

[Davidv]

Think of more frequent oil changes as an excuse to spend more time in your hangar looking at your airplane...

Once you develop a good method to get your filter off without spilling any oil it's a pretty relaxing exercise too.

[RobertGary1]

Changing the filter too often is not good. You don't be able to read the metals in it if it only has a few hours on it. I only change my filter every 50-100 hours. No need for any calendar schedule for the filter.

-Robert

[RLCarter]

Personally I change both at the same time (40~50hrs), but I don’t have a problem with those that change the filter every other time

[philiplane]

The longer 48110 (for Lycomings) or 48109 (for Continentals) filters are designed for 100 hours of service. You can drain the sump at 25 or 50 hour intervals and replace the filter at 100. You get a better debris sample at the longer interval. And if you're using filter media analysis in addition to oil analysis, a 25 hour filter won't tell you anything, a 50 hour filter will give you some details, and a 100 hour filter will give you the rest of the story. Oil filters are the same as air filters, they catch more material later than they do at the beginning of service.

[ilovecornfields]

What is a “better debris sample?” I get not wanting to change the filter because it’s extra work but that seems like some pretty ridiculous rationalizing to wait to get more crud in your filter before you realize something is wrong. If you’re depending on your oil to tell you something is wrong do you really want to wait a year to realize your engine is making metal?

If you want to know what the oil analysis would look like with twice as many hours just double the numbers. Not rocket science, guys.

Disclaimer: Not a rocket scientist but I was a chemist.

[EricJ]

4 minutes ago, ilovecornfields said:

What is a “better debris sample?” I get not wanting to change the filter because it’s extra work but that seems like some pretty ridiculous rationalizing to wait to get more crud in your filter before you realize something is wrong. If you’re depending on your oil to tell you something is wrong do you really want to wait a year to realize your engine is making metal?

If you want to know what the oil analysis would look like with twice as many hours just double the numbers. Not rocket science, guys.

Disclaimer: Not a rocket scientist but I was a chemist.

The idea is that you're looking for little metal and debris particles, flakes, whatever, caught in the filter media when you chop the filter open after removal from the engine.   Running the filter longer makes it more likely that you'll detect a low metal production rate because the filter will have caught more of the particles.

Having been through low and high metal production rates in my engine, running the filter longer to improve the ability to detect or compare particle/debris production is very practical.    If you just throw your filter out after removal from the engine and don't cut it open to inspect the media, then it's moot other than going through filters faster than you need to.

 

 

Edited March 12, 2021 by EricJ

[GeeBee]

It is true that Sulphuric acid is the primary acid you find in engine oil. However anytime you have carbon, crude carbon you have chances of creating phenol, or carbolic acid or its derivatives. Both of these are corrosive, however phenol is really hard to get out of oil because its boiling point is 359 F. So you really want to minimize carbon particles mixing with water vapor. Once it creates a phenol, the only control is the neutralizing capability of the oil.

 

[Hank]

Personally, I have never changed the oil in any engine without also changing the filter. Car, truck, lawn mower, airplane . . . . Now I just need to figure out what filter the golf cart takes.

[RobertGary1]

56 minutes ago, ilovecornfields said:

 

If you want to know what the oil analysis would look like with twice as many hours just double the numbers. Not rocket science, guys.

Disclaimer: Not a rocket scientist but I was a chemist.

The testing had limitations so doing a 1 hour oil change for instance may not be enough to detect metals. Same with filters. Our eyes are limited and we can only see a minimum critical mass. 

[ilovecornfields]

I get what you guys are saying, but unless the critical mass is 1 detectable unit, running the filter for half as long just means you have to decrease your threshold of what is “abnormal” to half as much.

This has been discussed before but the sole purpose of an oil change isn’t to change the oil but also to inspect “under the hood” and potentially detect minor problems before they turn into major ones. Just shoving a quick drain hose in the bottom and adding a few quarts of oil will not accomplish this. Just like with the preflight, most of the time it’s a “waste of time” except when you discover something potentially catastrophic. Did you guys read the NASA report this week where an airliner took off without a pitot tube which they later found on the ground?

No matter how you try to spin in (pun intended) twice the interval means twice as long until you potentially find something catastrophic. 

[N201MKTurbo]

2 hours ago, Davidv said:

Think of more frequent oil changes as an excuse to spend more time in your hangar looking at your airplane...

Once you develop a good method to get your filter off without spilling any oil it's a pretty relaxing exercise too.

When i was using the plane to commute (I did it for 20 years) the time to open and close the hangar doors and pull the plane out and put it back in is a significant factor in the trip time. 

[EricJ]

28 minutes ago, ilovecornfields said:

I get what you guys are saying, but unless the critical mass is 1 detectable unit, running the filter for half as long just means you have to decrease your threshold of what is “abnormal” to half as much.

And if that falls below the level of practical detectability, or lowers the SNR, then that is detrimental to the purpose.   It's like having an insufficient population sample size in any statistical process, if N is too small your data reliability will suffer.

Edited March 12, 2021 by EricJ

[rbridges]

Thanks. It's only been 4 months.  I run plane consistently, but just not putting as many hours between changes.  It's not about saving money, it's more about being lazy and not wanting to drop cowling to change the filter.  

[ilovecornfields]

6 minutes ago, EricJ said:

And if that falls below the level of practical detectability, or lowers the SNR, then that is detrimental to the purpose.   It's like having an insufficient population sample size in any statistical process, if N is too small your data reliability will suffer.

And what dangerous process in the oil change only shows up at 50 hours and is completely undetectable at 25 hours if you set the upper limit of normal at half the previous amount? If you were unsure of what you saw was signal vs, noise you’d still probably run it for 25 hours and check again so you didn’t really lose anything by checking early. On the other hand, if something is clearly abnormal at 25 hours then you found out months sooner than if you had waited until 50.

By that argument you should wait 200 hours between oil changes because then the SNR is really high!

I get the argument, but it just seems like a rationalization for being lazy instead of a real scientific argument based on reality. 

In the spirit of full disclosure, I don’t do my own oil changes. I text my A&P/IA when it’s getting close to oil change time and let him know when I don’t need the plane for a few days and leave out the oil, filter, Camguard and Blackstone container. He send me a text when it’s done and leaves a logbook sticker. If he finds something abnormal he send me a picture and we talk about it. I’d much rather have him looking under the hood then me because I have no clue what I’m looking for and he’s been doing this for 30 years.

[EricJ]

30 minutes ago, ilovecornfields said:

I get the argument, but it just seems like a rationalization for being lazy instead of a real scientific argument based on reality. 

In the spirit of full disclosure, I don’t do my own oil changes.

Yes, you don't have any experience but you're sure the people who do it are doing it wrong.

Uh-huh.

Sorry if the explanations go over your head, but it's a very practical issue.

 

 

 

[Skates97]

52 minutes ago, ilovecornfields said:

If he finds something abnormal he send me a picture and we talk about it. I’d much rather have him looking under the hood then me because I have no clue what I’m looking for and he’s been doing this for 30 years.

This isn't a comment about doing your own oil changes, but I would encourage everyone to take a look under the cowling on a regular basis, even if you have no idea what you are looking for. I can see a lot with a flashlight just looking through the door to check the oil and up through the cowl flaps. I didn't know much of anything four years ago about what to look for, but I would look anyway. I take a look during every pre-flight, you just don't know what you may or may not see, and if you look at it enough you will know when something just doesn't look like you think it used to.

[cliffy]

How much do you want to know about how to operate your 4 cylinder Lycoming?

There have been A&Ps who have had their license yanked when the FAA came a knockin' because they thought they knew more than Lycoming on how to maintain the engine

https://www.lycoming.com/sites/default/files/O-HO-IO-HIO-AIO %26 TIO-360 Oper Manual 60297-12.pdf

[ilovecornfields]

13 hours ago, EricJ said:

Yes, you don't have any experience but you're sure the people who do it are doing it wrong.

Uh-huh.

Sorry if the explanations go over your head, but it's a very practical issue.

 

 

 

Sorry, but I didn’t see an explanation to go over my head. I asked you to name the dangerous process that is invisible on a 25 hour oil change but readily apparent on a 50 hour oil change and instead you provided a personal attack.

I’m not sure what I don’t have “any experience” with. I’ve changed my oil, I just choose not to do it and I explained why. It really wasn’t that difficulty a task to do. Because I acknowledge I’m not an expert at something and delegate the task to someone who is that makes me a fool? Do you not understand that part of doing more frequent oil filter changes is to examine the engine and look for problems? You think I would get more out of looking at the engine than my experienced A&P/IA?

With respect to interpreting GC-MS data, I do have some experience. I used to run my own and interpret them when I was doing chemistry research (I did mention that if you’ll recall). I even ran my own proton NMRs and learned how to tune it by listening to the sounds of the protons relaxing. I’ve also spent 20 years working with statistical analysis so I think I have some experience there, too.  But I guess I don’t have the unique experience you do which make you able to definitively say exactly when oil filters should be changed, who should do it and why anyone who disagrees is a fool.

[Bartman]

Before my engine rebuild and pandemic I flew to a beach destination and back every other week. I know my plane well and my SOP was drain the oil after a return flight around 25-30 hours and refill with fresh oil before the next flight. The filter was changed every other oil change at about 50-60 hrs total. Since it’s just me flying the plane there is little risk of someone starting up with no oil, but I always put some painters tape covering the oil fill door and left the case of oil on the wing walk as another measure as a visual indicator. In the summer when I’m flying a lot I changed the filter every other oil change and do all work myself because I truly enjoy the involvement and have the skills to do it. Going into winter with less flying the oil and filter were both changed regardless of hours, and again in spring regardless of hours. 

In 2020 we completed a field overhaul and I have about 40 hours so far.  Given a new engine I am now servicing the oil more frequently and do the oil, filter, and sump screen.  I will continue this every 25 hours this year, but when I am comfortable I will likely go back to changing the oil every 25 hours and filter every other oil change, probably next year.