Oil Color

[Bob - S50]

Just a question.

We have a '78J and I've noticed that when I check the oil before flight, and the oil is cold, it is usually very dark.  However, if I check it after flight (maybe 10 minutes after shutdown), it is a nice honey color.

1.  Do others see the same thing?

2.  Why is that?

[ArtVandelay]

What is your definition of "cold"?

[DXB]

1. YUP, even with as little as 5 hrs on the oil, and low (1 qt/10hrs) oil consumption

2. dunno, wondered the same thing

[Oscar Avalle]

same with me...

[Awful_Charlie]

I've never looked after shutdown, except at oil change time, by which time it's pretty black!

[Hector]

Have not seen that. My oil starts honey color after an oil change and slowly turns darker. By around 20 hours it is a dark honey color (no longer translucent) and by close to 30 it is just dark. I change the oil around 25 hours when it starts to go dark. I'm in Florida so maybe it does not get cold enough to experience what you are describing.

[INA201]

I'm thinking that when the oil is hot it's thinner and less thickness on the stick so it appears more clear.  When the oil is cold the oil on the stick is probably twice as thick appearing darker.  

[Bob - S50]

57 minutes ago, INA201 said:

I'm thinking that when the oil is hot it's thinner and less thickness on the stick so it appears more clear.  When the oil is cold the oil on the stick is probably twice as thick appearing darker.  

That's what I was thinking but wanted to see if others thought the same thing without me influencing their input.  Thanks.

[Bob - S50]

20 hours ago, teejayevans said:

What is your definition of "cold"?

Anything from 30F to 80F.

[Bob - S50]

Glad to hear others see the same thing.  I thought maybe we were getting too much blow-by even though the compressions are good.  We currently burn a quart every 5 or 6 hours or so.  The way I know is we buy a case at oil change and put in 6 quarts.  When we've used up the other 6 quarts we usually have about 30 hours on the oil change.  We usually just do another oil change at that point rather than start buying individual quarts of oil.

[INA201]

Just my opinion but I consider cold when the plane has been sitting for 24 hours or more.  I'm burning roughly a quart every 5 hours or so in a 1978J.  

[ArtVandelay]

Just my opinion but I consider cold when the plane has been sitting for 24 hours or more.  I'm burning roughly a quart every 5 hours or so in a 1978J.  

Same year, same rate, but I think I'm losing oil thru the breather, exhaust pipe looks clean. I seem to lose at a higher rate when I'm doing multiple short hops and when oil has a few hours on it.

[INA201]

I don't have much oil on the belly, few drops under the breather after it sits a while(silver dollar size), and exhaust pipe is clean and dry. I guess mine is just burning it up for the most part with a little coming out of the breather.  Typically I fill to six quarts but haven't tried running any less to see if that would reduce the breather blow by any.

[Hank]

My last quart before a change, going in at 40+ hours, generally lasts 5-6 hours. I refill with 7 (6 for the engine and 1 for the filter), add the first usually 10-12 hours later. Each subsequent quart goes in a little sooner, often on 1/2 qt increments. Still don't quite use a case per 50-hour cycle. Higher power and higher RPMs increase oil consumption, though. When I fly lots of long distance trips, I use more oil; as local flying increases, oil consumption goes down.

Color wise, it's generally pretty good for the first two additions, and begins to darken up around 25-30 hours. By 50 hours, it looks about like my truck does around 5000 miles, when I change it. But 50 Mooney hours is over 8000 miles . . . .

[DXB]

On 12/20/2015 at 6:04 PM, Hank said:

 Higher power and higher RPMs increase oil consumption, though. When I fly lots of long distance trips, I use more oil; as local flying increases, oil consumption goes down.

I was a little alarmed recently when I flew 14 hrs total round trip to New Orleans - 8500-9500 msl, running WOT at 2500 rpm, and consumed about 2.5 quarts in the process.  I noted a bunch of oil on the left nose gear door and belly, none at the exhaust, and no sign of new leaks inside the cowl.  I thought I had a cylinder going soft.  But now that I'm back to doing local hops at 23 squared down low, I don't see anywhere near this rate of consumption- closer to my usual 1 per 10 hrs. 

I guess the additional 200 rpm produces much more blow by to pressurize the crankcase?  Is the nose up attitude for extended climbs also big factor in this in addition to the high rpms?  Also why do I have so much oil on my left nose gear door, which sits in front of the breather tube outlet??

[Hank]

You should find where the oil in the gear door is coming from, that does not sound normal to me.

What was your flight time on the trip to the Big Easy? Two and a half quarts sounds like a lot for the round trip, even if it was 5-6 hours each way. Your gear doors should stay clean. It's not uncommon for my oil burn to double on long trips like that, but I don't fly WOT; I tried that once, fuel,burn increased ~1-1/2 gph for a negligible speed increase. Instead, once I level off, I pull the throttle back enough to make the MP needle barely move, then set 2500 and lean. 

If I were to guess, higher oil consumption comes from two things:  full power climbs to higher altitude take more time, and higher RPM produces more power at any throttle setting. Our engines will never be as easy on oil as a car, simply due to the construction and need to operate in a wider temperature extreme; they aren't built as tight.

Edited April 24, 2016 by Hank

[DXB]

6 hours ago, Hank said:

You should find where the oil in the gear door is coming from, that does not sound normal to me.

What was your flight time on the trip to the Big Easy? Two and a half quarts sounds like a lot for the round trip, even if it was 5-6 hours each way. Your gear doors should stay clean. It's not uncommon for my oil burn to double on long trips like that, but I don't fly WOT; I tried that once, fuel,burn increased ~1-1/2 gph for a negligible speed increase. Instead, once I level off, I pull the throttle back enough to make the MP needle barely move, then set 2500 and lean. 

If I were to guess, higher oil consumption comes from two things:  high power climbs to higher altitude take more time, and higher RPM produces more power at any throttle setting. Our engines will never be as easy on oil as a car, simply due to the construction and need to operate in a wider temperature extreme; they aren't built as tight.

It was actually 7+ each way - so about 1 qt/ 5hrs - roughly double my usual local hop consumption - similar to what you describe.  Yeah I'd like to understand why there's oil on the left nose gear door though ( but none on the right).   And the inside of the cowl looks clean as always.  

[Shadrach]

Just now, DXB said:

It was actually 7+ each way - so about 1 qt/ 5hrs - roughly double my usual local hop consumption - similar to what you describe.  Yeah I'd like to understand why there's oil on the left nose gear door though ( but none on the right).  It's the same side as the breather outlet, but in front of it, so this makes zero sense to me. And the inside of the cowl looks clean as always.  

 

How many quarts did you depart with? Extra RPM will contribute to oil burn, but oil temp and age (read hrs on oil) also affects consumption rate.

[ArtVandelay]

I had oil coming out of the rear of the belly panel back by my stormscope antenna. Turned out it migrated along the control rods and dripped off where the linkages turn upward. Since the oil was dirty and i had a recent oil change (10 hrs) I chalked it up to a messy oil change.

The turbulence inside the cowl, landing gear can cause it to do travel in strange ways

[PaulB]

16 minutes ago, DXB said:

I was a little alarmed recently when I flew 14 hrs total round trip to New Orleans - 8500-9500 msl, running WOT at 2500 rpm, and consumed about 2.5 quarts in the process.  I noted a bunch of oil on the left nose gear door and belly, none at the exhaust, and no sign of new leaks inside the cowl.  I thought I had a cylinder going soft.  But now that I'm back to doing local hops at 23 squared down low, I don't see anywhere near this rate of consumption- closer to my usual 1 per 10 hrs. 

I guess the additional 200 rpm produces much more blow by to pressurize the crankcase?  Is the nose up attitude for extended climbs also big factor in this in addition to the high rpms?  Also why do I have so much oil on my left nose gear door, which sits in front of the breather tube outlet??

I've had the opposite experience with RPM and oil consumption.  While finishing up my commercial license I was routinely operating at 2200 RPM.  Oil consumption went from 1 quart per 10 hours to about 1 quart per 5-6 hours.  Now that I'm back to normal flying and cruising at 2500 I'm seeng 1 in 10 again.  Mike Busch mentions in his webinar on diagnosing high oil consumption (around the 59 minute mark) that this could be from the lower RPMs not allowing for as good of a seal on the cylinder rings due to low combustion chamber pressures.  That being said it could have been, like you mention, all the high deck angles during chandelles that caused the increased consumption.

[DXB]

4 hours ago, Shadrach said:

 

How many quarts did you depart with? Extra RPM will contribute to oil burn, but oil temp and age (read hrs on oil) also affects consumption rate.

I departed with 6 quarts, finished the trip with 5.2-ish, added 2qts along the way.  So 2.8 quarts consumed over 14 hrs flying.  I try to never fill above 6 except at the initial oil change.  The oil had about 7 hrs on it when I left, and this was the first oil I added.   

[Marauder]

4 hours ago, Shadrach said:  

How many quarts did you depart with? Extra RPM will contribute to oil burn, but oil temp and age (read hrs on oil) also affects consumption rate.

I departed with 6 quarts, finished the trip with 5.2-ish, added 2qts along the way.  So 2.8 quarts consumed over 14 hrs flying.  I try to never fill above 6 except at the initial oil change.  The oil had about 7 hrs on it when I left, and this was the first oil I added.   

Dev -- if I fill to 7, I'm guaranteed to be spending some belly cleaning time.

Also, I find the consumption rate is higher if I have more hours on the oil. Not sure if there some fuel dilution involved but the closer to an oil change I am, the higher the consumption rate. How many hours are on the oil?

[DXB]

4 hours ago, Marauder said:

Dev -- if I fill to 7, I'm guaranteed to be spending some belly cleaning time.

Also, I find the consumption rate is higher if I have more hours on the oil. Not sure if there some fuel dilution involved but the closer to an oil change I am, the higher the consumption rate. How many hours are on the oil?

Ah- poor wording on my part.  Meant it was 7 hrs since last oil change.  I left with 6 and never add oil to above 6.

[Bob - S50]

22 hours ago, DXB said:

...Also why do I have so much oil on my left nose gear door, which sits in front of the breather tube outlet??

That's where we notice oil too.  Comes out the breather which is located just above that door.

[Browncbr1]

On April 24, 2016 at 11:09 AM, DXB said:

I was a little alarmed recently when I flew 14 hrs total round trip to New Orleans - 8500-9500 msl, running WOT at 2500 rpm, and consumed about 2.5 quarts in the process.  I noted a bunch of oil on the left nose gear door and belly, none at the exhaust, and no sign of new leaks inside the cowl.  I thought I had a cylinder going soft.  But now that I'm back to doing local hops at 23 squared down low, I don't see anywhere near this rate of consumption- closer to my usual 1 per 10 hrs. 

I guess the additional 200 rpm produces much more blow by to pressurize the crankcase?  Is the nose up attitude for extended climbs also big factor in this in addition to the high rpms?  Also why do I have so much oil on my left nose gear door, which sits in front of the breather tube outlet??

Here is my theory.  Others may have a differing ideas on this, but this is what I have come to believe after similar symptoms.  

The right side of your prop has higher angle of attack, particularly in take off and climb and slower IAS, which results in more air being pushed through the right side of the cowl and more cooling on that side.   It produces more pressure in the cowl than the left side.   There is a certain airspeed and rpm when air starts to maybe stop or start to reverse through the oil cooler if in its oem configuration.   This difference in pressure from the right and left sides of the cowl generate tons of wind going from right to left under the motor.  And oil leaking from or around the case and dripping straight down or even on the right side of the engine will get blown to the left cowl cheek and left gear door.   I think this is why many of us have "chafe leaks" that go out the left cheek and down the left side of the fuse.   I have noticed that folks who have modified cowls perhaps don't seem to have this issue?  I assume mooney knew this and this is why the put the oil cooler on the left side    

Feel free to tell me I'm totally wrong, but I just thought this was one of the design flaws of the OEM cowls.