DXB

Do ambient temps or oil type affect oil consumption?

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I track my oil consumption obsessively, borescope my cylinders regularly, and do my own spark plug maintenance.  Last spring I noted a sudden change in my oil consumption from 1qt/12-15hrs to 1qt/5-7 hrs. The only cylinder that has not been IRAN'd or replaced in the last few years had oily top and bottom plugs and extra oil pooled in the combustion chamber. Because compression was fine, I assumed a stuck oil control ring.  In August I flushed that cylinder with MMO, and I was satisfied to find the plugs were no longer oily, and there was less oil pooled inside.  Oil consumption seemed to decrease slightly (to 1qt/7-8hrs) but did not return to baseline.  A few weeks ago after the first cold snap, I changed from my summer oil (Aeroshell 100W + Camguard) to my winter oil (PhillipsXC 20W50 + Camguard). I've since put 14 hours on the fresh oil and still haven't consumed a full quart!  Looking back on it, the sudden decrease in oil consumption in the spring coincided not only with the first warm temps but also my changing from winter to summer oil.   What's going on here?! Some half-formed ideas:

- Did an oil control ring get stuck and then unstuck coinciding perfectly with the season change?  I seriously doubt it.  The MMO trick did really seem to make the aging cylinder of concern pool less oil though.  

-Do the two different oils have different tendencies to burn or get blown out the breather?   I again  doubt it.  Also, I did notice a bit less consumption in September and October, which makes me think it is really the outside temperatures.  This was a period when I had 100W approaching 50 hours on it, so consumption should have been increasing instead.

-If ambient temps are the critical factor, then is it oil temp, CHT, or air temp at the breather outlet that is the critical factor?  My CHTs are under reasonable control by C model standards (summer: hottest cylinder always <400 in cruise, can reach ~420 in climb; winter: no CHT issues at all in climb or cruise).

Does anyone else see this phenomenon? Do you know the mechanism?  Google was of no help. And  I reviewed Mike Busch's "On Engines" opus without any insight.  Could someone maybe ask Mike for me?

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CHTs are very often higher as OAT increases...

Higher CHTS lead to softer materials, more prone to wear...

Higher CHTs also lead to higher OilTs that have a tendency to lower the viscosity and ability to lubricate...

Over a long period of time...

  • rings wear...
  • cylinder surfaces wear...

Using a bore scope, you can peer into the cylinder looking for the cross hatches to see how worn they are?

As the cross-hatches wear, the oil tends to escape more...

It may be time for new rings and a cylinder OH...(?)

Start with the bore scope...

PP thoughts only, not a mechanic...

Oil type has a lot of viscosity differences... the thinner the viscosity (more water like) the more chances it has to escape as clearances increase...
 

See if Brian has some thoughts... @orionflt  Brian, Got a bore scope? :)

Best regards,

-a-

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34 minutes ago, carusoam said:

Using a bore scope, you can peer into the cylinder looking for the cross hatches to see how worn they are?

As the cross-hatches wear, the oil tends to escape more...

It may be time for new rings and a cylinder OH...(?)

Start with the bore scope...

Oil type has a lot of viscosity differences... the thinner the viscosity (more water like) the more chances it has to escape as clearances increase...
 

See if Brian has some thoughts... @orionflt  Brian, Got a bore scope? :)

 

Anthony - I borecope myself regularly- the cross hatches are visible on the 3 cylinders that have been reworked or replaced, absent on the one old one that was previously oily but is now much improved.  Oil viscosity for my summer vs. winter oil should differ when cold but be the same at operating temps - so I don't see how that alone could account for the observation.  I have no symptoms that could convince me to pull one or more cylinders at this point.  I'm just curious about this striking change in oil consumption with season change - what really surprised me is that consumption went way down again with cold weather!

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Anthony has some good points, I’ll just comment further to say that at operational temps in cruise the 20w-50 vs straight 50 is the same viscosity, or very very close.

Only difference is the 20w 50 is thinner at cold temps so in theory more could get though larger tolerances until warmed up but I think we’re splicing hairs.

If the oil became over heated say 250f. The 20w-50 oil would be thicker than the 50 because the viscosity modifiers will continue to reduce the rate at which the 20w oil thins, until the point it gets to hot and the modifiers shear, but that’s really really hot like 300f ++.

Off topic, as i am a big fan of multi weight oil as it protects the engine Better at at start up and in overheat conditions. 50w, is better at storage as when it cools it thins at a slower rate, so at room temps it is thicker (50w vs 20w) and stays on cylinders for a longer period of time during storage.

Just a private pilot (not a chemist). That line was for Anthony .


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49 minutes ago, aaronk25 said:

Anthony has some good points, I’ll just comment further to say that at operational temps in cruise the 20w-50 vs straight 50 is the same viscosity, or very very close.

Only difference is the 20w 50 is thinner at cold temps so in theory more could get though larger tolerances until warmed up but I think we’re splicing hairs.

If the oil became over heated say 250f. The 20w-50 oil would be thicker than the 50 because the viscosity modifiers will continue to reduce the rate at which the 20w oil thins, until the point it gets to hot and the modifiers shear, but that’s really really hot like 300f ++.

Off topic, as i am a big fan of multi weight oil as it protects the engine Better at at start up and in overheat conditions. 50w, is better at storage as when it cools it thins at a slower rate, so at room temps it is thicker (50w vs 20w) and stays on cylinders for a longer period of time during storage.

Just a private pilot (not a chemist). That line was for Anthony emoji3.png.


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Your comments and Anthony's are tangential to my query.  I am quite familiar with the viscosity properties of multiweight oil, which make them more favorable to limit wear at startup in winter. And I agree the oil grade itself is an unlikely explanation of my observation:  markedly reduced oil consumption in cold ambient temperatures. That link is admittedly tenuous and anecdotal in my case, and so I was wondering if anyone else has observed the same thing, and what a mechanism might be. My increase in oil consumption in last summer could have resulted from progressing cylinder wear, but the dramatic (almost 2-fold) improvement as soon as temps dropped was pretty unexpected without any engine work or a major change in  usage profile.

Also there is no basis I'm aware of for saying that multiweight aviation oil provides better startup protection at summer ambient temps or overheat protection at any ambient temp.  Synthetic oils do breakdown less at high operating temps I believe, but I don't use the part synthetic aviation oils (Aeroshell 15W50, Exxon Elite 20W50), so that is not an explanation. 

Edited by DXB

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Your comments and Anthony's are tangential to my query.  I am quite familiar with the comparable viscosity of strait weight and multiweight oil at operating temps. And I agree the oil grade itself is an unlikely explanation of my observation:  markedly reduced oil consumption in cold ambient temperatures. That link is admittedly tenuous and anecdotal in my case, and so I was simply wondering if anyone else has observed the same thing, and what a mechanism might be. My increase in oil consumption in last summer could simply result from progressing cylinder wear, but the dramatic (almost 2-fold) improvement as soon as temps dropped was pretty unexpected without any engine work or a major change in  usage profile.
Also there is no basis I'm aware of for saying that multiweight aviation oil provides better startup protection at summer ambient temps or overheat protection at any ambient temp.  Synthetic oils do breakdown less at high operating temps I believe, but I don't use the part synthetic aviation oils (Aeroshell 15W50, Exxon Elite 20W50), so that is not an explanation.  I am quite familiar with the viscosity properties of multiweight oil, which make them more favorable to limit wear at startup in winter.


Ed Collins did a seminar on multi-weight oil. Covering both topics, I think I layed the logic out why multi weight protects better at higher oil temps. A 50w oil is still pretty thick compared to 20w at 65f, Given most of the engine wear occurs at start the sooner oil can be pumped the better. A lighter weight oil will always offer quicker cold start lubrication compare to a 50w.


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Just had an idea while procrastinating from my real work.  Could it be that my plane dumps oil out the breather mainly at high deck angles, and the cold of the winter makes me pitch up much less initially to get good climb rates?  I'm not sure this makes total sense only because I typically maintain a steady 5 degrees nose up  in either season once I'm above 1000 ft AGL during initial climb .  I also fill the sump to 6L only, so overfilling is not part of the problem.  

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Dev,

I wrote some additional ideas... but the memory required to keep it all straight still eludes me...

So... now you hit on one of the topics I was going to share is the last thing you wrote...

So... I’ll try again... somewhere in the middle, I can’t recall if summer or winter causes your oil to go missing... but the logic may help your thought process...   :)

See if Aaron can add any order to this as well...

Best regards,

-a-

...........
interesting...

One thing that does change in winter...

The ICP increases... internal cylinder pressure increases with the MP...

If there was a large oil usage... related to T/O power in the summer... and then better in the winter...

Bit of a stretch here... the seal improved with higher ICP... (?)


So... if the oil usage is good all winter... and gets even worse as summer approaches...

Sounds like the viscosity change is responsible for oil escaping...

An example where this is done intentionally... is oil for high mileage vehicles... where the viscosity is increased to keep it from escaping...

The cost is in higher operations cost of a less efficient motor... more gas, to operate the engine you already own...

 

Other things to keep in mind...

How the oil may also escape.... Does cold weather make it get out of the case vent any easier? Do you climb at a higher angle in the winter because you can? (Opposite of what Dev is seeing)

 

I would really think about the oil viscosity being responsible... the names used, are really quite ‘nominal’... where the actual viscosity under real operating conditions may be the reason...

You might actually be seeing an improvement with oil use, because of its actual viscosity at the temp and time...

 

rings are a two way street...

  • They hold back the exhaust from getting in the oil...
  • They hold the oil back from getting into the cylinder above the piston...

When things really wear out...

  • the oil gets foamy and smells like exhaust... and turns far black in a few hours after an oil change...
  • The oil pools in the bottom plug, shows up at the exhaust tip, and disappears by the quart in less than the usual 9hours...

Viscosity of old oil also seems to change...

The first quart to need to be replaced after an oil change seems to be done at 10 hours... then 9 hours for the next quart...  As you get towards 50 hours or more on the oil... the replacement rate seems to increase...

This is an oddity, I never quite got a hold of... too many variables for a proper experiment...

It would be really interesting if we could measure viscosity Changes of our own oil... 

Even if we could get our oil to last forever.... the stability packages will still wear out... from a chemistry / oxidation point of view...

 

What would happen if you were to leave the summer oil in the plane in NJ all year...?

  • Warm up may take a bit longer... to make sure the OilT is in the operating zone...
  • waiting for the warm up of thick oil can pose a challenge to the engine parts that are waiting for splash lubrication...
  • Oil usage would drop back to summer style...

 

 

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Have you noticed how many hours before the oil turns darker after an oil change with each oil? This would be an indication of bypass through the rings. If one type of oil turns darker quite faster than the other then he difference in viscosity is making a difference on how much bypass you are getting through the rings. I can tell you in my plane it takes around 22 hours or so before the oil loses its translucent new appearance. I use XC-20/50 year round so unfortunately I can’t give you a point of reference but you use both oils and I’m wondering if you have noticed any difference.


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10 hours ago, Hector said:

Have you noticed how many hours before the oil turns darker after an oil change with each oil? This would be an indication of bypass through the rings. If one type of oil turns darker quite faster than the other then he difference in viscosity is making a difference on how much bypass you are getting through the rings. I can tell you in my plane it takes around 22 hours or so before the oil loses its translucent new appearance. I use XC-20/50 year round so unfortunately I can’t give you a point of reference but you use both oils and I’m wondering if you have noticed any difference.


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It's a good thought and I wondered the same thing - I am indeed super OCD about watching this stuff ;).  I notice the oil still turning dark at pretty much the identical rate as before even though consumption plummetted now- first seeing it is looking slightly dusky at 7-10 hours.  I expect it will take 15-20 to turn pretty dark if it is  the same as before.

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14 hours ago, carusoam said:

One thing that does change in winter...

The ICP increases... internal cylinder pressure increases with the MP...

If there was a large oil usage... related to T/O power in the summer... and then better in the winter...

Bit of a stretch here... the seal improved with higher ICP... (?)

I actually like this idea - I've no idea if it's true, but at least it fits my observations.

14 hours ago, carusoam said:

Sounds like the viscosity change is responsible for oil escaping...

An example where this is done intentionally... is oil for high mileage vehicles... where the viscosity is increased to keep it from escaping...

I remain skeptical of the oil viscosity explanation. Fresh winter and summer weight oils really should be pretty similar in viscosity at operating temps I would think.  Also oil consumption did also improve a bit in September and October, before I changed to winter weight oil.  That summer oil had 30-50 hours on it during this period and so should have been disappearing faster, not slower, if the ambient temps were not a factor.  Of course I did flush the rings of the problem cylinder with MMO in early August, so I have a hard time separating any benefit from that intervention.  

14 hours ago, carusoam said:

How the oil may also escape.... Does cold weather make it get out of the case vent any easier? Do you climb at a higher angle in the winter because you can? (Opposite of what Dev is seeing)

I was thinking along similar lines, as I note in my last post above.  But in the end I have no clue if my deck angle is any different by season - one could imagine that I might not climb at a decreased pitch because I get the climb rate I want more easily, but I kinda doubt it - instead I probably exploit the extra performance by using a similar pitch.  The climbs in summer would certainly take longer in the summer, which might be part of the explanation. The oil also gets hotter in climb (200-210F) in summer as opposed to winter (low 190s max).  

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12 hours ago, Hector said:

Have you noticed how many hours before the oil turns darker after an oil change with each oil? This would be an indication of bypass through the rings. If one type of oil turns darker quite faster than the other then he difference in viscosity is making a difference on how much bypass you are getting through the rings. I can tell you in my plane it takes around 22 hours or so before the oil loses its translucent new appearance. I use XC-20/50 year round so unfortunately I can’t give you a point of reference but you use both oils and I’m wondering if you have noticed any difference.


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I have this issue in my Saratoga. The oil  turns dark very quickly, and I am also using quite a bit of oil. The engine is about 1700 since overhaul (overhauled in 2001) but it runs great; all of the other parameters are excellent, compressions, temps, egt spread, etc. . What is the solution to this short of a top overhaul (which I wouldn’t do this close to TBO),  if any? I am assuming that not all of the cylinders have blow by, so would the answer be to isolate the offending cylinders and re-ring?

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There are a few things about oil consumption that I know, and a lot that I don't.

What I know:

Oil escapes by way of rings, valve guides, crankcase vent, leaks. You have to figure out which when chasing oil consumption.

Some oil necessarily gets past the rings because the cylinder walls need lubrication or they will wear out more rapidly. As the walls wear, the cross hatching disappears.

What I don't know:

Why do Continentals seem to consistently use less oil than Lycomings?

What's the best oil level for a Lycoming IO-360 for minimum consumption? Everyone seems to have their favorite. My experience with a lot of Lycoming 320-360 cu in engines over the years was to run them at seven and add a quart when it got down to 6. Many seem to find lower oil consumption with lower levels. I  tried running between 6-7 for about 50 hours and 5-6 for about 50 hours after break-in in my Lycoming factory rebuilt IO-360-A3B6 and there was no difference. 

Does oil type (single viscosity or multi-viscosity) affect consumption? I recently changed from AS W100 to Philips XC 20W50 and in seems that the consumption has decreased, but it is too soon to have statistically meaningful data. I also added CamGuard to the Philips. Did that make a difference in consumption? (Hard to see how, but who knows?...)

Here's a document I found a while back from AeroShell that states that "tighter engines" (I think he means cylinder to ring tightness) burn less oil on multi-viscosity oil, but he doesn't explain why.

video-transcript-oil-consumption.doc

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28 minutes ago, Bravoman said:

I have this issue in my Saratoga. The oil  turns dark very quickly, and I am also using quite a bit of oil. The engine is about 1700 since overhaul (overhauled in 2001) but it runs great; all of the other parameters are excellent, compressions, temps, egt spread, etc. . What is the solution to this short of a top overhaul (which I wouldn’t do this close to TBO),  if any? I am assuming that not all of the cylinders have blow by, so would the answer be to isolate the offending cylinders and re-ring?

I think I would try the Marvel Mystery Oil trick described in this thread, and probably do it to all of your Saratoga's cylinders.

https://mooneyspace.com/topic/31082-mmo-or-other-oil-control-ring-tricks/?tab=comments#comment-521368

After that, run the engine for a few hours, and if your oil gets black again quickly, check all of your spark plugs.  Re-ring the one cylinder (or 2) that has the most oil on the spark plugs.  Worst case, if you can determine which cylinder is the culprit, remove and IRAN to repair the cross hatch of that cylinder.

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26 minutes ago, PT20J said:

There are a few things about oil consumption that I know, and a lot that I don't.

What I know:

Oil escapes by way of rings, valve guides, crankcase vent, leaks. You have to figure out which when chasing oil consumption.

Some oil necessarily gets past the rings because the cylinder walls need lubrication or they will wear out more rapidly. As the walls wear, the cross hatching disappears.

What I don't know:

Why do Continentals seem to consistently use less oil than Lycomings?

What's the best oil level for a Lycoming IO-360 for minimum consumption? Everyone seems to have their favorite. My experience with a lot of Lycoming 320-360 cu in engines over the years was to run them at seven and add a quart when it got down to 6. Many seem to find lower oil consumption with lower levels. I  tried running between 6-7 for about 50 hours and 5-6 for about 50 hours after break-in in my Lycoming factory rebuilt IO-360-A3B6 and there was no difference. 

Does oil type (single viscosity or multi-viscosity) affect consumption? I recently changed from AS W100 to Philips XC 20W50 and in seems that the consumption has decreased, but it is too soon to have statistically meaningful data. I also added CamGuard to the Philips. Did that make a difference in consumption? (Hard to see how, but who knows?...)

Here's a document I found a while back from AeroShell that states that "tighter engines" (I think he means cylinder to ring tightness) burn less oil on multi-viscosity oil, but he doesn't explain why.

video-transcript-oil-consumption.doc 67 kB · 2 downloads

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Thanks - the first expert commentary I’ve seen that suggests what I’m observing might be a real phenomenon - maybe I should try running multigrade next summer and see what happens.

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If your plane is similar to my J the winter oil temps at say 5c are 165-170, unless the oil cooler gets the winter block off aluminum tape across 1/2 of it. In the summer 25c oil is 190f-200.

We know viscosity Is thicker at lower oil temps. Is your oil temp lower in the winter? If so the thicker oil may not be consumed/blown overboard at the same rate as thinner (hotter) summer temps.


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9 hours ago, aaronk25 said:

If your plane is similar to my J the winter oil temps at say 5c are 165-170, unless the oil cooler gets the winter block off aluminum tape across 1/2 of it. In the summer 25c oil is 190f-200.

We know viscosity Is thicker at lower oil temps. Is your oil temp lower in the winter? If so the thicker oil may not be consumed/blown overboard at the same rate as thinner (hotter) summer temps.


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Also a reasonable hypothesis  - though I generally get oil temps up to 180 in the winter so I don’t need to block the oil cooler. 

Edited by DXB

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Interesting claim on the Phillips X/C aviation oil website: "It provides distinct performance benefits compared with single-grade engine oils, including...reduced oil consumption in most engines." I'm now wondering if that's not just marketing BS.  It's certainly consistent with my observations, though I still have no clue what the mechanism would be, or whether it could account for an almost 2-fold difference in my case. Maybe the ambient temps are irrelevant.  I'm may keep running it into summer next year and see what happens.

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1 hour ago, Rinj said:

Any particular reason you don't just run the phillips all year long?

That’s what I do as there are often temps in the 30s or 40s in the morning followed by 80s in the afternoon in the higher elevations out west.  

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2 hours ago, Rinj said:

Any particular reason you don't just run the phillips all year long?

Mainly Mike Busch's strong recommendation to use W100 straight weight whenever possible, because it adheres to critical components longer after engine turned off and cooled, thus in principle providing longer corrosion protection.  I'm not sure of the hard evidence for it though, so I am open to change at the moment. 

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Isn't that what Camguard is for?  So you can run a 20w50 oil for starts that are easier on the engine, especially at lower temps, or if the temp delta is significant, but to still have the corrosion protection from Camguard?

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56 minutes ago, tmo said:

Isn't that what Camguard is for?  So you can run a 20w50 oil for starts that are easier on the engine, especially at lower temps, or if the temp delta is significant, but to still have the corrosion protection from Camguard?

I am not aware of any evidence that Camguard fully negates loss of corrosion protection when multiweight oil runs off the cam /lifters faster at higher ambient storage temps - are you?

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No, I am not, hence the questionmarks - genuinely asking.  Especially that I have 20w50 in my engine and will likely replace with same, for various reasons.  Adding Camguard sounds like something that makes sense - won't hurt anything, might help.

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