Head scratching oil burn in '16 Outback 3.6

Messages
70
Location
Colorado
So here's an interesting one I can't seem to figure out and isn't making much sense to me...

I have a 2016 Outback 3.6 and love the car for what it is. Other than this "issue" the motor and the rest of the car are in great shape with plenty of abuse and 83k miles with most of any needed work or maintenance done by myself and have had since new. Oil changes have always been consistent at 6k miles give or take on synthetic when back in North Texas, then when moving here to Colorado at 5k for Syn and 4k to 5k for "conventional" blend depending on driving. So never any really long OCI's or even pushing it with this car in its life.

Anyway, the motor doesn't really burn much oil at all during an entire OCI...MAYBE 1/4 a quart if there's lots of off roading or mountain driving during but even then it's only sometimes and is really a non issue.

Here's the head scratcher I can't figure out....I still drive back and forth to Dallas from Denver every 3 to 4 months consistently. On the drive DOWN to Texas, I'll ALWAYS burn between 1/2 a quart to 3/4 of a quart of oil. I'll top off when I arrive of course the next day, however on the drive back to Denver the motor won't burn a single drop. What point I am in the OCI doesn't matter it seems to always happen to the same degree, and the brand or type doesn't seem to matter with the exception that I used a little bit less than usual on the drive down with a HM blend.

It's definitely not a situation where the oil has been short tripped (my car rarely is) for a while then burns off excess fuel, water etc. The motor barely burns any oil during an OCI or even long highway drives unless it's the drive down to Dallas and only then one way.

I can't figure it out and even fellow mechanic buddies can't seem to figure it out. Could it have something to do with changing altitudes or pressures going DOWN only? And where could it "be going"? Past the piston rings and into the cylinder? And then why? lol

The motor obviously seems just fine otherwise and as long as it's topped off afterwards has no issues. I've never even experienced a low oil light in the thing...but this one way drive is the only thing it doesn't seem to like. Anyone here have any experience with something like this before by chance?
 
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279
Lots of down grades going from Denver to Texas? This is common on stick cars also that are downshifted for engine braking.
this creates a high manifold vacuum that the cylinders have to work against and can pull oil past the rings.
I was thinking along similar lines ...
 

Subie5w30

Thread starter
Messages
70
Location
Colorado
Lots of down grades going from Denver to Texas? This is common on stick cars also that are downshifted for engine braking.
this creates a high manifold vacuum that the cylinders have to work against and can pull oil past the rings.

Hmmm....interesting thought there! It's a CVT and not a stick but RPMS tend to stay consist with more up's than down's but the effect would be similar in my mind. At least in theory. It's definitely a very gradual decline over the 800 mile drive and in fact the first 200 miles or so you're actually climbing a bit from Denver but this is an interesting theory to look more into actually....def the best idea at the moment!
 
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226
Location
eastern WA
Lots of down grades going from Denver to Texas? This is common on stick cars also that are downshifted for engine braking.
this creates a high manifold vacuum that the cylinders have to work against and can pull oil past the rings.
this is great info. i have a 65 GTO with a manual trans that has always used oil, both before and after an engine refresh. i just kinda thought old cars tended to use oil! but the car never needs brakes, because i use engine braking all the time.

this may very well be one of those rare cases where someone posts a question on the internet and it gets resolved accurately without a lot of ambiguity or argument.
 

Subie5w30

Thread starter
Messages
70
Location
Colorado
Do you drive down to TX 98mph & back at 62mph? or it's the above guy^ with the high manifold pressure.

Ha! The speed's are pretty identical just different directions and grades. I typically just set the cruise between 3 to 5mph over the speed limit sp depending where I'm at on the drive between 78/80mph and 73/75mph with exception of slowing down through towns etc.

this is great info. i have a 65 GTO with a manual trans that has always used oil, both before and after an engine refresh. i just kinda thought old cars tended to use oil! but the car never needs brakes, because i use engine braking all the time.

this may very well be one of those rare cases where someone posts a question on the internet and it gets resolved accurately without a lot of ambiguity or argument.

The more and more I think about it, and throw in the nature of CVT's in how they "take care of the engine braking" for you....the more this theory is growing on me too and making more and more sense. And in the past with all my manual cars (miss those sometimes!) moderate oil burn was definielty more of an occurrence there as well.
 
Messages
226
Location
eastern WA
Ha! The speed's are pretty identical just different directions and grades. I typically just set the cruise between 3 to 5mph over the speed limit sp depending where I'm at on the drive between 78/80mph and 73/75mph with exception of slowing down through towns etc.



The more and more I think about it, and throw in the nature of CVT's in how they "take care of the engine braking" for you....the more this theory is growing on me too and making more and more sense. And in the past with all my manual cars (miss those sometimes!) moderate oil burn was definielty more of an occurrence there as well.
my wife has a 2014 outback with a 2.5 and a CVT, about 70k miles. the car has not used any oil that I recall, but she drives only around Spokane and just not that many hills. Denver to Dallas is a very different story.
 

4WD

Messages
16,644
Location
Texas
this is great info. i have a 65 GTO with a manual trans that has always used oil, both before and after an engine refresh. i just kinda thought old cars tended to use oil! but the car never needs brakes, because i use engine braking all the time.

this may very well be one of those rare cases where someone posts a question on the internet and it gets resolved accurately without a lot of ambiguity or argument.
Wow, BiL had the two speed and 389 … and yes, used oil before/after overhaul …
But oh man … That 1st gear used to pull some outrageous burn outs …
 
Messages
226
Location
eastern WA
Wow, BiL had the two speed and 389 … and yes, used oil before/after overhaul …
But oh man … That 1st gear used to pull some outrageous burn outs …
four speed and a 505 these days! but now I want to do some testing, drive it for a few months like I normally do and then drive it for a few months actually using the brakes.

funny but whenever i drive my wife’s subaru i switch the CVT over to manual mode and do a lot of engine braking, but she never does it. i bet her car has used more oil with me driving it than with her!
 
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1,045
Location
South East Asia
My wild guess this can be related to the angle of the car during driving, since subaru using boxer engine where the piston is horizontal, when the car driven in downward/upward for prolonged period, the oil may pass the ring or valve seals
 
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2,337
Location
South Carolina
Lots of down grades going from Denver to Texas? This is common on stick cars also that are downshifted for engine braking.
this creates a high manifold vacuum that the cylinders have to work against and can pull oil past the rings.
Exactly what I was thinking. When was the last time the PCV was checked/changed?
 
Messages
15,873
Location
N.H, U.S.A.
So here's an interesting one I can't seem to figure out and isn't making much sense to me...
.......

Here's the head scratcher I can't figure out....I still drive back and forth to Dallas from Denver every 3 to 4 months consistently. On the drive DOWN to Texas, I'll ALWAYS burn between 1/2 a quart to 3/4 of a quart of oil. I'll top off when I arrive of course the next day, however on the drive back to Denver the motor won't burn a single drop.
......
Oh that's an EASY one.

And a sustained trip, You will be burning off the sump dilution of water and fuel, then having exercised the engine you will have cleaned up the rings a bit.
Cars that " don't burn a drop" actually DO, its unavoidable.
The missing lube is replaced by gas and water and other blowby products.

HTH,

- Ken
 
Messages
1,259
Location
NC
Lots of down grades going from Denver to Texas? This is common on stick cars also that are downshifted for engine braking.
this creates a high manifold vacuum that the cylinders have to work against and can pull oil past the rings.
Stick shift owner here. Going uphill isn't much of a problem. Going downhill with engine braking - I got cars backing off for a mile behind me due to the wonderful blue smoke clouds from my little oil burner (2000 Honda CR-V, 5-speed, AWD). When I had a 2014 Nissan Rogue with CVT it would adjust the RPMs while going down a mountain, so I think the downhill oil burning does apply to the CVT vehicles.
 
Messages
545
When I was driving in the West with long downgrades with my '87 Mitsubishi pickup I'd let the engine brake the speed. It would always use oil when I did that. With other normal driving it wasn't an oil burner. I believe driving from Texas to Denver with the overall gain in elevation would account for the OP's oil use in his vehicle.
 

Subie5w30

Thread starter
Messages
70
Location
Colorado
Exactly what I was thinking. When was the last time the PCV was checked/changed?

I actually changed the PVC around 60k miles just as a preventative thing, but honestly the previous one was in perfect shape as well so neither should be much of a problem.....I hope. :)
 
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