Mooney Oil Change Interval (Poll)

[201er]

When do you change your oil? Do you do it based on hours or months?

[Mooney 217RN]

I religiously change my oil and filter at or before 25 hrs Nothing wrecks an engine faster than dirty oil.

Edited March 20, 2022 by Mooney 217RN

[Utah20Gflyer]

I’ve been doing oil analysis at every change at approximately 50 hours and they always come back with the oil being in good condition.  This could be influenced by the fact that I am adding a quart every 6 hours, essentially I do an oil change between each oil change.   If the oil analysis indicated the oil was in less than stellar condition at 50 hours I would shorten the interval until it did. 

[toto]

I selected “25” because that’s the Mooney interval but my complete answer is “both 25 and 50.”

In the Mooney, I change every 25 hours and currently running XC with CamGuard. I normally do every other oil change myself. In the Piper, the change happens at 50 hours with Aeroshell 15w50 and the shop has to do it because of a recurring AD on ECi cylinders that requires a compression test at 50.

For what it’s worth, the 50-hour interval running synthetic oil got about 2600 hours out of the O-360 in the Piper before voluntarily taking it down for overhaul. The engine was perfect at that time, with clean oil analysis and good compression, but I was getting superstitious about the TBO and felt like it was on borrowed time. The engine hasn’t run as well since then  

[ohdub]

I generally try to change it at 25 hours or 4 months, whichever comes first. If I'm flying a lot, I'll sometimes let it go to 30ish hours.

[larryb]

Every 25 hours.  And I do it myself. I like to take my time and really check over the engine compartment for wire and hose chafing, missing screws, loose screws. I lube exhaust slip joints with Mouse Milk. I lube the cowl flap linkage. I do have an oil filter cutter and cut open and inspect the oil filter every time. Check for exhaust leaks and fuel leaks. 

[EricJ]

40 hours.   Which isn't an option so I can't vote.    It's rigged!    :'(

 

 

[47U]

25 hrs, and four(ish) months.  My typical flight is less than 2 hrs.  If I’m on a long cross country, I’ll extend the hours until I get home.

I cut the filter and pull the sump screen every time.  I had an engine shop tell me that even more important is to get a paint filter (that goes over the top of your pail) from Home Depot and screen the oil as it drains.  I also use a clean pail and inspect the bottom for shiny stuff after I dump the oil into my haz waste transport can.

 

[Mooney 217RN]

2 hours ago, larryb said:

Every 25 hours.  And I do it myself. I like to take my time and really check over the engine compartment for wire and hose chafing, missing screws, loose screws. I lube exhaust slip joints with Mouse Milk. I lube the cowl flap linkage. I do have an oil filter cutter and cut open and inspect the oil filter every time. Check for exhaust leaks and fuel leaks. 

Almost every one of my oil changes I do on my own.  For the reasons you mention above.  The only real downside to the Ovation is that the oil change is a bitch compared with the E Model I flew for almost 20 years.  I had a LoPresti Speed Cowl on the E Model.  I could disengage the linkage on the cowl flap, pull it down, and easily reach the quick drain without removing the lower cowl.  The Ovation requires complete cowling removal to do an oil & filter change.

[A64Pilot]

Four times a yr, every three months, which means I don’t get to 50.

We don’t change oil because it breaks down, even garbage oil will go way past 50 hours.

We change oil because it gets loaded up with contaminates, acids and carbon and lead for example, so of course the oil will test fine, because it is. So we change oil to get rid of the contaminates, not because the oil is breaking down.

Aircraft oil leads an easy life, it doesn’t get very hot, and the loads placed on it are actually pretty low, but aircraft engines are loose so there is lots of blow-by and that dirties up the oil.

[Mooneymite]

7 hours ago, Mooney 217RN said:

I religiously change my oil and filter at or before 25 hrs Nothing wrecks an engine faster than dirty oil.

Obviously, there's no such thing as changing oil "too frequently", but I come up with a big zero when I try to recall damaged engines from habitually infrequent oil changes.

Today's oil is pretty darn resilient.  If your engine goes past TBO with annual oil changes, is that "good enough"?

Some $90 lawn mowers are sold today that never need oil changes...  I suspect a $40,000 aircraft engine may be able to withstand 50 hours, or 1 year between oil changes.

 

 

[carusoam]

There are interesting heat related, and chemistry related break downs of oil molecules on some engines…

Low oil flow in really hot places can be tough on the oil’s chemistry…

Exhaust valve lubrication is one area…

Turbo bearing lubrication is another…

As long as oil continues to flow through these areas as designed… everything is good….

Sometimes the flow gets diminished, and its residence time increases…. And the molecular break down becomes autocatalytic….

If you have heard of reaming carbon out of valve guides…. This is oil that has broken down and is becoming a diamond in a diamond factory….

Other discussions circulate around turbos and their infamous cool down periods after landing… there are proper ways of keeping the oil healthy in this situation as well… the cool down period isn’t one of them…. The heat at the TIT sensor is pretty high… well above the degradation temp of oil… keep the oil flowing through here… it has a really high flow rate as it lubricated and cools the turbo parts…

 

Acids are the by-products of combustion… acids can be tough on the oil’s molecular weight as well…

Lots of oil details going on at the same time… 
 

Go MS!

Best regards,

-a-

[A64Pilot]

Turbos are a little different, you need to let them cool enough so the oil doesn’t burn off and form coke after shutdown, same thing is going on in valve guides, excessive oil is getting in and it burns off and forms coke.

Many auto turbos have gone to water cooled center sections to prevent that, but that’s not an option for us, usually all it takes is two min at idle to cool a turbo enough to prevent coking.

Bottom line is the oil is at its best coming out of the bottle, from then on its a downhill slide, you get to decide how far down it gets before you have to change it.

IF we had a very fine bypass oil filter, then maybe I could get behind extending oil change intervals, but we don’t so I’ll waste a little money on oil changes, although I’ll admit to never having seen an aircraft engine fail from not having its oil changed, but I have seen bearings etched and corrosion on valve stems etc that likely came from acid.

What oil analysis is exceptionally good at is determining the condition of the oil, unfortunately it’s most often sold as an engine analysis, but if you do oil analysis, pay particular attention to TAN, TBN, fuel content etc, analysis can tell you if your not getting your oil hot enough. Not getting it hot enough is more of a problem than overheating, oil max oil temp limits are no where near the max for oil, they are engine temp limits, oil can easily handle much higher temps.

Average Auto oil temp is in the low to mid 200’s, and it lasts what 10,000 miles? Average auto speed isn’t as high as we think, it’s really less than 30 because we spend a lot of time stopped or in slow traffic, so 10,000 miles is more than 300 hours.

Now aircraft engines are not auto engines, but I’m trying to point out that at 50 hours aircraft oil itself is in great shape still, but it’s full of stuff you don’t want in your oil

[slowflyin]

I started with the turbo cool down method but have since moved on.  I think it's probably as cool as it's going to when exiting the runway.   I've been back and forth over the years, but the GAMI guys swayed me eventually.  

[EricJ]

17 hours ago, Mooneymite said:

Obviously, there's no such thing as changing oil "too frequently", but I come up with a big zero when I try to recall damaged engines from habitually infrequent oil changes.

Today's oil is pretty darn resilient.  If your engine goes past TBO with annual oil changes, is that "good enough"?

Some $90 lawn mowers are sold today that never need oil changes...  I suspect a $40,000 aircraft engine may be able to withstand 50 hours, or 1 year between oil changes.

Oil breaks down in heat, even really good synthetic stuff, and eventually you get too much dirt and other crap suspended in it.   

 

[A64Pilot]

It does break down in heat, but maybe that heat is hotter than we realize. When I put 29” tires on my Maule in Summer in S Ga the oil temp would hit 225 in a climb and run about 200 in cruise. I chased everything, vernatherm etc to find nothing wrong, so I called Exxon to ask if I should shorten oil change intervals as well the high temp problem was obviously mostly from reduced airspeed more than anything being wrong and I couldn’t fix it.

Guy pretty much laughed and said from an oil perspective my temps were right where they wanted, oil wise they don’t get concerned with temps until over 300 or so, however he did reiterate that I should be concerned if my temps were outside of the engine manufacturers limits, that those limits were engine, not oil limits.

Turbos can be a different animal, especially if the oil flow is low they can heat the oil in the turbo quite hot, and as we measure oil temp before it goes through the engine we may not see that localized heat.

Oil break down from heat results in a viscosity breakdown, and oil analysis ought to catch that. I believe straight weight oils get thicker, while multi viscosity oil get thinner, due to the breakdown of the Viscosity Improver package. 15W-50 oil is of course 15 weight oil treated to not thin out as it gets hot.

Edited March 22, 2022 by A64Pilot

[Mooneymite]

On 3/21/2022 at 11:31 AM, EricJ said:

Oil breaks down in heat, even really good synthetic stuff, and eventually you get too much dirt and other crap suspended in it.   

I agree with you.  Everyone would agree with you.  Oil does get dirty and degrades over time.

The issue isn't, "Does oil get dirty?", the poll is about how frequently oil needs to be changed.

While we can change oil after every flight and not hurt it, it begs the question of how frequently it must/should be changed.

Lycoming recommends O-360 (with an oil filter) oil change at 50 hours.  Since Lycoming sets TBOs, I suspect this hour-based recommendation is conservative.  The big variable is oil consumption.  If one burns a quart every 10 hours, how "used" is the oil at the 50 hour recommended change?

Yes, I know there is a recommended time interval as well, but are we actually shortening our engines life expectancy, by going the full 50 hours?

 

[EricJ]

1 hour ago, Mooneymite said:

I agree with you.  Everyone would agree with you.  Oil does get dirty and degrades over time.

The issue isn't, "Does oil get dirty?", the poll is about how frequently oil needs to be changed.

While we can change oil after every flight and not hurt it, it begs the question of how frequently it must/should be changed.

Lycoming recommends O-360 (with an oil filter) oil change at 50 hours.  Since Lycoming sets TBOs, I suspect this hour-based recommendation is conservative.  The big variable is oil consumption.  If one burns a quart every 10 hours, how "used" is the oil at the 50 hour recommended change?

Yes, I know there is a recommended time interval as well, but are we actually shortening our engines life expectancy, by going the full 50 hours?

 

I suspect 50 hours with a filter is conservative, since most such guidance is.

BMWs (iirc) used to have an optical sensor that looked at passing oil and indicated a change when it got too dark.   That's a proxy for dirt/crap suspension, but doesn't evaluate how much breakdown has happened due to heat.   In the race cars if we ever had an overheating event past a particular temperature we'd change the oil, regardless of how fresh it was, because it would have lost much of it's best lubricating capabilities.

Without specific knowledge or testing of a particular engine's oil or close examination of temperature history, there's not much way to know exactly when is an optimal time to change it.   So generally we use the guidelines, which are probably conservative.    My oil turns black pretty quickly after a change, even though the compression measurements are very good, so I try to change it around 40 hours, maybe a little less in the summer if it got hot during a climb or two.   YMMV.

I think this is also why a lot of people say it's not a big deal to extend an oil change in a pinch or skip a change in the filter.   Unless it's really dirty or been hot, it's probably fine, but enough engines get dirty and/or hot that the guidelines probably cover the majority of cases.

[ArtVandelay]

Given the oil filters are back ordered until who knows when, my 2 week spruce order status is still on hold, I might be increasing my normal 35 hour interval.

[daytonabch04]

1 hour ago, ArtVandelay said:

Given the oil filters are back ordered until who knows when, my 2 week spruce order status is still on hold, I might be increasing my normal 35 hour interval.

What size oil filter?  This one is in Stock.  Ordered mine 2 weeks or so ago and received it- no issues. 

Champion Oil Filter 48110-1 (vansaircraft.com)

Edited March 23, 2022 by daytonabch04

[Vance Harral]

For what it's worth, after years of agonizing over this, we stopped changing oil based on hours, and instead consistently change it based on calendar time every 4 months.

Yes, I know this doesn't make sense at first glance.  But hear me out.

The annual/100-hour inspection guidelines for our airplanes require the oil be changed at annual.  Of course we had incidents over the years where we wound up having an oil change at annual with an absurdly low number of hours on the oil and filter, which is frustratingly wasteful.  Changing oil based on calendar intervals eliminates this problem.

Changing oil based on calendar intervals also simplifies the problem of ordering supplies: we order from the same providers at the same times - usually a year's worth of supplies at a time.

This strategy does mean engine run hours between changes varies, but honestly not that much.  In a "good" year we might put 140 hours on the airplane, with almost half of that occurring during the nice flying months in the middle of the year.  In a "bad" year we might only put about 70 hours on the airplane.  But in general, the oil winds up being changed somewhere between 25-60 hours of operation, with the longer hour intervals occurring over shorter time periods with slightly more make-up oil inbetween.  Altogether, this is an entirely reasonable strategy.  I know anecdotes are not data, but we've been running things this way for the past decade, and our engine is currently at 31 years and about 2300 hours since overhaul.  Nothing adverse showing up in compression checks, oil analysis, and borescope inspections at every change, our only complaint is that we're beginning to get a number of small seeps at the oil pan gasket and crankcase spine thread, just because everything is three decades old.  But we can live with that, and we'll keep running it this way until it talks to us.

[A64Pilot]

I agree with the calendar oil change, it’s what I do.

See oil should be changed upon hitting x number of hours or a recommended calendar interval, whichever comes first. For me the calendar interval does, if I flew a lot more hours, then I may hit the hours first, but I don’t and think I’m not in the minority.

[Mooneymite]

3 minutes ago, A64Pilot said:

I agree with the calendar oil change, it’s what I do.

This poll starts at 6 months for calendar changes, but all the responses (so far) have been hours.  If you fly 200 hrs/ year, the 3 months and 50 hours might happen at the same time...for the rest of us, the calendar is our friend.

[ArtVandelay]

What size oil filter?  This one is in Stock.  Ordered mine 2 weeks or so ago and received it- no issues. 
Champion Oil Filter 48110-1 (vansaircraft.com)

That’s the one…interesting spruce show “no stock”.
I’ll give it a little more time before I cancel it.