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why do we change our oil filters so often?

KayS

Well Known Member
Happy Easter Everybody!

lycoming says to change oil with screen at 25 and with spin on filter every 50 hours. oil filters should be replaced all 50 hours and probably most of us stick to that advise, me too. but why?

i see one advantage that is checking the filter for abnormal abrasive on a regular basis. but other than that?

when i look at the large filter area i think that if a filter stops doing it's job due to glogging debris and coked stuff, the engine would have stopped long before.

i don't want to start an oil/filter interval war, just trying to understand our engines.

Kay
 
The design and history of our engines is the reason. They have 70 plus year old ditch pumps and tractor motors in their history. Low compression, lots of blow by, lots of lead, oil gets contaminated easily compared to modern engines.

Regular oil and filter changes are the cheapest maintenance you will ever do to a Lycoming or Continental and give it a long and healthy life.

We change oil and filter at either 25-30 hours or 6 months whichever is sooner. The calendar time is just as important due to the contaminants in the oil.
 
1) if you don’t replace the filter you retain old oil left in filter. putting 6-7 quarts of fresh oil that mixes with the ~1 quart of dirty oil in the filter seems like wasting fresh oil. Before even starting the engine the oil is already 15-20% dirty or think of it already having 15 hours on it.
2) oil filters are cheap, about the same cost as a quart of oil.
3) Gives me something to do while oil drains
4) you can’t real make a big oily mess unless you change the filter.
 
We change oil and filter at either 25-30 hours or 6 months whichever is sooner. The calendar time is just as important due to the contaminants in the oil.

Did I miss something? :confused:

Here’s what Lycoming recommends in their service letter:

A. 50-hour interval oil change and filter replacement for all engines using a full-flow oil filtration system.

B. 25-hour interval oil change and screen cleaning for all engines employing a pressure-screen system.

C. Even if the aircraft is flown only a few hours, a total of four months maximum between changes for both systems listed under “A” and “B.”
 
oil filters are cheap, about the same cost as a quart of oil?

"oil filters are cheap, about the same cost as a quart of oil."

where? Last aircraft oil filter I bought was $23! The oil was 5.75/quart.
 
I follow the manufacturers recommendation because I want the engine to perform and last as long as the manufacturers claims. Best way to get the life and performance out of the engine is to follow the manufacturers recommendation.

50 hour oil and filter change sounds reasonable. Most internal combustion engine manufacturers have similar recommendations. Many autos have 10,000 mile oil changes. IF my RV-6 is flying at 180 MPH, the 50 hour change is 50*180=9,000 miles. If only 150 mph, then 50*150=7,500 miles. Toyota has a recommended 10,000 mile oil change on the Prius and GMC has 7,500 mile change on the old 4.3L V6 pickup. John Deere has 100 hour oil and filter change for a Kawasaki engine on the commercial zero turn mower I cut my yard with.

As I get older, I tend to change oil based on calendar time in service before I get the recommended time limit because of lack of use.

Oil and filter is cheap compared to the cost of a replacement engine.
 
Carlos,

What we do is similar enough... I wouldn't leave oil in for 50 hours unless it was flying daily ;)
 
50 hour oil and filter change sounds reasonable. Most internal combustion engine manufacturers have similar recommendations. Many autos have 10,000 mile oil changes. IF my RV-6 is flying at 180 MPH, the 50 hour change is 50*180=9,000 miles. If only 150 mph, then 50*150=7,500 miles. Toyota has a recommended 10,000 mile oil change on the Prius and GMC has 7,500 mile change on the old 4.3L V6 pickup. John Deere has 100 hour oil and filter change for a Kawasaki engine on the commercial zero turn mower I cut my yard with.

As I get older, I tend to change oil based on calendar time in service before I get the recommended time limit because of lack of use.

Oil and filter is cheap compared to the cost of a replacement engine.


Our planes have a four month oil change recommendation, but I’ve never seen a time period put on vehicles. Why? Can the time recommendation safely be disregarded?
 
Our planes have a four month oil change recommendation, but I’ve never seen a time period put on vehicles. Why? Can the time recommendation safely be disregarded?

Most automobiles have a recommendation to change oil at least annually.
 
Our planes have a four month oil change recommendation, but I’ve never seen a time period put on vehicles. Why? Can the time recommendation safely be disregarded?

Actually newer vehicles have a time limit on their oil changes just like our aircraft. Most now have sensors to let you know when it's time to change the oil and the mileage varies with your style of driving (speed, idling time, towing, etc). If you dig into the owners manual, you most likely will find a time limit for the oil change. Either that or it will show up on the dashboard screen as to when you are due regardless of the mileage since the last change. All black magic stuff :D
 
Ah come on! What else do you have to do with all your money. Changing oil is fun, right?
I change mine every 25 hours or so.
Our aircraft engines have so much clearance piston to wall it would drive and auto mechanic crazy. They are built way looser than race car engines and they are loose.
Oil is the cheapest part of the maintenance of an engine.
Pour it in. Art
 
Our aircraft engines have so much clearance piston to wall it would drive and auto mechanic crazy. They are built way looser than race car engines and they are loose.
Oil is the cheapest part of the maintenance of an engine.
Pour it in. Art

Piston wall clearance on a Lyc is .0025-004, if I remember correctly. Exactly the same as an old school Chevy small block. Low end on the ring gap is also the same as a small block (around .025), though the high end of tolerance is a bit wider. I am failing to see how an .003 piston wall clearance increases blowby. Morr than enough clearance in the ring lands to keep this from getting the ring out of alignment with the wall.
 
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lycoming says to change oil with screen at 25 and with spin on filter every 50 hours. oil filters should be replaced all 50 hours and probably most of us stick to that advise, me too. but why?

Why not?

For my part...I see the cost of oil and filter change as a very small percentage of the total cost of ownership of an airplane. And...as with all of my other vehicles, I'm not prepared to second-guess the engine manufacturer regarding maintenance of the engine that they designed and built, so I just go with their recommendations. I figure that they're smarter about these engines than I am.

I know little about airplane engines. I have to take someone's advice regarding their maintenance...seems like it makes for sense to go with the engine manufacturer's advice rather than SGOTI.

YMMV (literally)
 
Let’s see: 50 hours @ 200 mph = 10,000 miles. Most car manufacturers want you to change your oil more frequently than that. :rolleyes:
 
Unleaded

When we finally get to using unleaded fuel, I will consider a longer oil change interval. But with all the lead we are pumping through the oil nowadays, I think the present change interval is reasonable.

I really really want to change to unleaded fuel. It will make the sticky valves go away, allow the use of full synthetic oil so we will have virtually no wear ( as long as we have roller cams!), allow the use of fuel management devices so will have a “both” position on the low wings to prevent running out of fuel with one tank full, and be healthier. Did i already say I cant wait?
 
Let’s see: 50 hours @ 200 mph = 10,000 miles. Most car manufacturers want you to change your oil more frequently than that. :rolleyes:

Comparing aircraft engine longevity/oil change intervals to autos is not exactly apples-to-apples.
For one thing, auto engines rarely run continuously at 75% power.
 
Comparing aircraft engine longevity/oil change intervals to autos is not exactly apples-to-apples.
For one thing, auto engines rarely run continuously at 75% power.

Amen. So, even more justification for changing airplane engine oil.:D
 
The Lycoming is considered a heavy duty engine. Somewhere in the history is a plot of particles in the crankcase vs hours. These typically begin the increase after oil change then stablize. Particle generation does not stop, but the filter captures them at the same rate they are produced.

The change period is adjusted based on field experience, many oil parameters for corrosion, wear, oxidation, viscosity increase, water collected and lead.

We have basically the same engines, same fuel, same oils and same considerations, so I change at 50 hrs or less.

Fact: oil with a higher particle count wears all contacted components faster than clean oil. This is why diesels will have centrifugal separators and bypass filters that are much more efficient than the standard full flow filters. Bearings were more shiny, bore wear, valve stem, cam rollers and other parts all showed less wear. Although common sense, it has been validated and quantified with multiengine data.
 
Hey folks: the original question was for a technical explaination why to change our filters. Pupose was educational.

now that discussion jumped of rails completeley. statements like "it's so cheap", "manufactureer says so" and "have nothing to do anyway" aren't helpful. this thread turned into information garbage.

I herewith withdraw the question but feel free to add to the nonsense.

edit: thank you Bill for the good explaination. just saw your post after pressing the submit button.
 
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Technically

Well technically, not changing the oil filter while changing the oil is liken to taking a shower and not changing underwear. Technically, it can be done , but ewwwww.
 
that discussion jumped of rails completeley

a trait of VAF...

There might be more answers to your question, but IMHO the two most important ones are:
- early detection of oil contamination, I call it On Condition Maintenance. As an example, a C-90 last year on my field was found having plenty of aluminum chips in the filter. Given any more time, those could have caused a blockage of any of the internal oil passages, resulting in a catastrophic engine failure. I borescoped said engine and found that the piston pins on 2 cylinders were producing this aluminum. Replacement of those 2 cylinders and this engine happily hums along today :)
- might have heard of the term detergent... this means the oil will take in a lot of the nasty stuff the engine produces, such as acids, carbon residues, and more. Oil can only take so much, similar to a sponge... fresh one will absorb better ;)
 
1) if you don’t replace the filter you retain old oil left in filter. putting 6-7 quarts of fresh oil that mixes with the ~1 quart of dirty oil in the filter seems like wasting fresh oil.

There is no way that an oil filter holds a quart of oil. Ain't gonna happen. Having said that, I change the filter anyway. I wish I could change the oil in the cooler and other places that hold oil, but you can only get so much oil out of an engine. I find that 25 hour oil changes work for me, and pretty much agrees with the time in service recommendation.

-Marc
 
Most automobiles have a recommendation to change oil at least annually.

I once let my 2003 GMC 4.3L V6 go more than a year but less than the recommended oil change time. The valves started making noise till the engine warmed up. Added an additive to the oil, ran till cold noise went away, changed the oil and have changed the oil every 12-months even if it does not have the recommended miles.

IF there were no recommendation, one may hear the engine talk to you to change the oil if you are lucky.
 
I saw an episode of Top Gear / Grand Tour where one of the hosts said that the fuel injection system in a modern Ford Focus has more computational power than the entirety of NASA during the Saturn V missions. Comparing a modern car engine with all the automated controls, sensors, etc with an aircraft engine that gives you just RPM and temperature is a bit of a mismatch. As I build my plane and install my engine, it really is becoming apparent to me that when I leave my car and enter my hangar, I appear to be warping in time back about 60 years in the level of technology. Maybe more.
 
Back to the OP:

Ten years ago I did an oil change after coming home from a long cross country of about 22 hours.

Upon inspecting the oil filter at that change, I caught the huge problem shown in the picture below.

This was the crankshaft gear, which runs some important stuff. It was easy to spot some of the missing metal in the oil filter.

If I'd blown off cutting open the filter (or not changed it), the outcome most certainly would have been an engine failure.

Don't ever take cutting the oil filter open as a box checking exercise, as doing so may save your engine, plane and perhaps your life.
 

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Back to the OP:

Ten years ago I did an oil change after coming home from a long cross country of about 22 hours.

Upon inspecting the oil filter at that change, I caught the huge problem shown in the picture below.

This was the crankshaft gear, which runs some important stuff. It was easy to spot some of the missing metal in the oil filter.

If I'd blown off cutting open the filter (or not changed it), the outcome most certainly would have been an engine failure.

Don't ever take cutting the oil filter open as a box checking exercise, as doing so may save your engine, plane and perhaps your life.

Alex, your evidence is a good reminder to all of us.
Guilty, I have a filter waiting for me on the bench.
 
Hey folks: the original question was for a technical explaination why to change our filters. Pupose was educational.

now that discussion jumped of rails completeley. statements like "it's so cheap", "manufactureer says so" and "have nothing to do anyway" aren't helpful. this thread turned into information garbage.

I herewith withdraw the question but feel free to add to the nonsense.

edit: thank you Bill for the good explaination. just saw your post after pressing the submit button.



These threads on VAF wander this way and that - that makes them so useful. Yes, your original question may have been answered, but the thread acts as a reminder to others to have a think about how they want to operate their aeroplane. The manufacturers recommendation is usually a good base line, but in this case it assumes a lot more use than we give our engines - hence some caution and practicality being expressed.

Getting sniffy about replies won't aid the discussion. I would politely suggest you have a look at some other posts and see that they meander this way and that and some gems of advice from many of the Sages that frequent this organ are given ;):p
 
Slight thread drift

I’m surprised no one has mentioned the K&P/Challenger permanent oil filters. They are a little pricey, but the only replacements are an inexpensive o-ring and a long interval filter element.

Cleaning the element is easy in an ultrasonic cleaner and you get a good look at whatever debris was trapped.

Happy with mine on the RV-7 and a new one is mounted remotely on the firewall of our yet-to-fly RV-10.
 
Challenger oil filter - yep. I’m in to the “free” territory on mine. Plus ez To see debris and to clean.
As to oil in cooler, I had a drain plug added to my 9row, firewall mounted cooler. Still drain it all at 30 hours.
 
The OP has an interesting question.
As I see it the filter is a media filter only. It does not treat the oil.
Therefore the dirtier it gets the better it works. The dirt becomes a filter in itself. Air conditioning air filters are that way. If you change your air filter once a month you may be doing yourself a disservice. A waste of money and the filter would have filtered better left a little dirty.
Expensive commercial air filters are changed when the air restriction becomes larger than desired. The equipment usually has a manometer to measure the resistance.
So, as DanH says, measure and make a decision from the results.

I change my oil filter every oil change. About 30 hours.
 
The OP has an interesting question.
As I see it the filter is a media filter only. It does not treat the oil.
Therefore the dirtier it gets the better it works. The dirt becomes a filter in itself.

I take exception to this school of thought. I'm pretty sure that the oil filter manufacturers have a different idea about dirt in an oil filter. Indeed, at some point the filter could become so dirty that the bypass opens and the filter is useless.

Air conditioning air filters are that way. If you change your air filter once a month you may be doing yourself a disservice. A waste of money and the filter would have filtered better left a little dirty.

HVAC air filters are a whole 'nother animal. Filter performance is controlled by the MERV rating. The designer/manufacturer of the system should have a recommendation about the efficiency of the filter media as it also affects airflow and performance of the system. You can read about MERV ratings here:

https://www.grainger.com/know-how/e...nn4aoRRhmTQTS93KXFhoC5nwQAvD_BwE&gclsrc=aw.ds

Engine manufacturers also have recommendations but I'm willing to bet they don't say "Dirty is better".

-Marc
 
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I take exception to this school of thought. I'm pretty sure that the oil filter manufacturers have a different idea about dirt in an oil filter. Indeed, as some point the filter could become so dirty that the bypass opens and the filter is useless.



HVAC air filters are a whole 'nother animal. Filter performance is controlled by the MERV rating. The designer/manufacturer of the system should have a recommendation about the efficiency of the filter media as it also affects airflow and performance of the system. You can read about MERV ratings here:

https://www.grainger.com/know-how/e...nn4aoRRhmTQTS93KXFhoC5nwQAvD_BwE&gclsrc=aw.ds

Engine manufacturers also have recommendations but I'm willing to bet they don't say "Dirty is better".

-Marc

I've been around for a while and have never seen an oil filter dirty enough to bypass. I know that cleanable filters such as the K&N air filters used in some RVs filter better when they are a little dirty.
 
Piston wall clearance on a Lyc is .0025-004, if I remember correctly. Exactly the same as an old school Chevy small block. Low end on the ring gap is also the same as a small block (around .025), though the high end of tolerance is a bit wider. I am failing to see how an .003 piston wall clearance increases blowby. Morr than enough clearance in the ring lands to keep this from getting the ring out of alignment with the wall.

A good friend of mine was reading the thread and would like to correct Larry :)

Comrade,

LR172 made a huge error in his representation of piston to cylinder wall clearance, almost by a factor of 10. I am very
surprised nobody commented on it, because it is a very important number. I think it would be very informative to the group to know that
air cooled engines have up to 10 times the piston clearance as car engines, hence that loud clacking noise at idle before the piston heats up.
Because an air cooled engine can see 500F cylinder temps, and a car 200F, running clearances must be much bigger. This is also why a proper
warm-up is vital before takeoff.

The service limit at the top ring land of the piston is .032, not .003, like LR172 states. Definitely contributes to blowby and dirty oil.

Ivan
 

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I’m not a pilot, but I would like to become one, I am not a filtration expert, but I used to change filters for them. So, with that understood I may be able to elucidate some general ideas about large filter operations that may be applicable to aircraft engines.

This applies only to mechanical filtration, chemical filtration using media beds or ion exchanger, and centrifugal filters think Dysons, old Alfa Romeos and some large diesels work very differently.

Generally, a well-designed mechanical fluid filter will remove more and smaller particulates the longer they are in service, this is called ripening or conditioning the filter. In some applications filters are ganged in groups and the group that is in-service the longest is the final, or polishing filter. The reason being this filter has caught the most particulate and it is currently capable of removing the most and smallest particulates in the working fluid. This also allows the filters further up the chain to ripen into effectiveness.

As a filter ages or ripens in-service the pressure required to move the fluid thru the filter increases, at some point this pressure can over-come whatever is causing the system circulation, alternatively the media of the filter can physically tear failing the filter. For this reason, filters are changed. I would suspect both of these would be bad in an aircraft engine, but bypasses may allow the engine to continue to be lubricated and cooled, and if they open before the media tears, I would suspect very little damage to the engine. (I'm not a pilot, and the only air-cooled engine I maintain runs a lawnmower).

In large filtration operations each filter or gang of filters is fitted with pressure gauges on either side of the filter, the delta between the gauges is used as a proxy to how much life is left on the filter, and how loaded with particulates (dirty) the filter is. When those gauges display a predetermined delta, the filter is changed.

So, it may be that you are costing yourself more in filters and unnecessarily fouling engines by changing the filter at every oil change. I would suspect putting pressure gauges on either side of the filter could generate some useful data as to when a filter should be changed.

Please understand this is a very simplified version. There are some points such as, particulates that are mechanically held by a filter chemically polluting the working fluid that might also come into play here. Also if the filter is not correctly designed it may not become more effective at removing particulates over time (ball bearings caught in a colander won’t keep silt out of your drink).
 
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Hey folks: the original question was for a technical explaination why to change our filters. Pupose was educational.

now that discussion jumped of rails completeley. statements like "it's so cheap", "manufactureer says so" and "have nothing to do anyway" aren't helpful. this thread turned into information garbage.

I herewith withdraw the question but feel free to add to the nonsense.

edit: thank you Bill for the good explaination. just saw your post after pressing the submit button.


Dear Kay, don't be exasperated. I am not aware that any of Doug's rules for VansAirforce specifies that the person who starts the thread owns the thread forever. I have personally found that starting a thread on VansAirforce is a bit like having a child...you always have expectations, but in the end they tend to go their own way, and more often than not they usually turn out OK.

If the cattle wander however, you are certainly permitted to politely round them up a bit, but in this case I doubt that is necessary. Actually I think that the wandering has in fact produced some quite interesting and informative comments.

Personally I change filters at 50 hours but change oil at 25 hours. My oil always remains slightly transparent. I like that. I suspect the engine likes it too. :)
 
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.... I have personally found that starting a thread on VansAirforce is a bit like having a child...you always have expectations, but in the end they tend to go their own way, and more often than not they usually turn out OK.

If the cattle wander however, you are certainly permitted to politely round them up a bit, but in this case I doubt that is necessary. Actually I think that the wandering has in fact produced some quite interesting and informative comments. ...
Well said, Bob!
 
now we have some very interesting inputs, thanks. i herewith withdraw from withdrawal.

posting rules on VAF don't ban to meander, but they also don't ban to be snapped a bit.

i got the idea of changing filters now and think 50 hours intervals are reasonable.

btw... a filter here is much more expensive than a quart of oil. i paid 35 euros for a filter lately which equals to around 4,5 qts of aeroshell 100 W plus. so over time filters become a significant number we have to take into account.
 
I'm told that a Mann 940/4 filter is a good alternative - I just bought 3 from Amazon.fr and will have a look at the dimensions. All the youtube videos I've seen seem to show that Mann filters are good. And they are made in Germany. I could not find this exact filter on Amazon.de for some reason.

Also strangely, I paid only 6.76 Euro, but now the price is over 13 Euro.

Mann Filter W9404 oil filter amazon.fr order.png
 
Are there any automotive or other (tractor, boat, motorcycle....) oil filters that can be used?
 
Oil cooler

1) if you don’t replace the filter you retain old oil left in filter. putting 6-7 quarts of fresh oil that mixes with the ~1 quart of dirty oil in the filter seems like wasting fresh oil. Before even starting the engine the oil is already 15-20% dirty or think of it already having 15 hours on it.
2) oil filters are cheap, about the same cost as a quart of oil.
3) Gives me something to do while oil drains
4) you can’t real make a big oily mess unless you change the filter.

I too used to think like you but you also have a quart in the coooler that doesn’t get changed.

Gary
 
I've been around for a while and have never seen an oil filter dirty enough to bypass. I know that cleanable filters such as the K&N air filters used in some RVs filter better when they are a little dirty.

I maintain that there is no correlation between air and oil filters, and I'm pretty sure that K&N would never say "Don't change or clean your filters until they become a little dirty because they work better."

The whole "dirty is better" notion is not supported in any Lycoming Doc that I have seen.

-Marc
 
I would politely suggest you have a look at some other posts and see that they meander this way and that and some gems of advice from many of the Sages that frequent this organ are given ;):p

Excellent advice, and it's always enjoyed more when so ably written by Mike in the Queen's English! :)
 
Back to the OP:

Ten years ago I did an oil change after coming home from a long cross country of about 22 hours.

Upon inspecting the oil filter at that change, I caught the huge problem shown in the picture below.

This was the crankshaft gear, which runs some important stuff. It was easy to spot some of the missing metal in the oil filter.

If I'd blown off cutting open the filter (or not changed it), the outcome most certainly would have been an engine failure.

Don't ever take cutting the oil filter open as a box checking exercise, as doing so may save your engine, plane and perhaps your life.

Years ago there was a filter (ADC I think) that was a flat filter that had about a 6" disc screen that filtered down to about 20 microns. This filter held only about a tablespoon of oil. As the disc did it's work, there was a switch that would let you know when to clean it. There was also a metal detection indicator that would let you know of a problem.

It all sounded so good...... but back then filters were cheap.
 
I maintain that there is no correlation between air and oil filters, and I'm pretty sure that K&N would never say "Don't change or clean your filters until they become a little dirty because they work better."

The whole "dirty is better" notion is not supported in any Lycoming Doc that I have seen.

-Marc

Actually, K&N says exactly that on their air filters. I cut ever filter and wash the element. Never find more than a trace of "stuff" after 50 hours. Car engines have gone from oil changes every 1,000 miles to many recommending 10,000 mile intervals. I do Blackstone Labs oil analysis every oil change and the additives are never depleted after 50 hours. I still go with 50 hour oil changes out of force of habit.
 
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