Why do engines burn/consume motor oil?

[Rex]

My question is about oil consumption in the engine. Some engines use oil, others do not. Not all engines use oil at the same rate. So I ask..

What is the number one reason why oil is consumed during use? (Engine characteristics, oil quality, other?)

If it’s the specific engine design, what would be the best solution to eliminate and/or minimize oil consumption (different oil weight or oil manufacture, adding an oil additive, or other?).

If it’s the oil used inside an engine that’s known not to “burn” oil, what is it about the oil that breaks down to the point of its consumption?

I’m looking for the serious respondents only with quality answers. Big thanks!

 

[QUIKSVT]

Oil will get by piston rings, valve seals and thru the PCV system. A lot of variables.
Josh

 

[Merkava_4]

People get consumption because they're using a thinner oil than necessary.

 

[jhellwig]

My truck uses oil because of a lovely gas saving feature. It has done it since about 30 thousand miles.

 

[zach1900]

Umm because they internal made to burn a small amount of oil.

 

[zach1900]

My engine burns a ton of oil. Help!!!!!!! That's the topic title when a bitoger engine burns 5oz over 10K miles.

 

[demarpaint]

Originally Posted By: jhellwig
My truck uses oil because of a lovely gas saving feature. It has done it since about 30 thousand miles.


That gas saving feature wouldn't be DI would it?

 

[jhellwig]

Originally Posted By: demarpaint
Originally Posted By: jhellwig
My truck uses oil because of a lovely gas saving feature. It has done it since about 30 thousand miles.


That gas saving feature wouldn't be DI would it?

Nope. It is due to the active fuel management ie dissable 4 cylinders and let the oil that carys over the poorly designed pcv baffle and coke the rings till it uses even more oil mode.

My wife's car is di and doesn't use any oil.

 

[demarpaint]

Originally Posted By: jhellwig
Originally Posted By: demarpaint
Originally Posted By: jhellwig
My truck uses oil because of a lovely gas saving feature. It has done it since about 30 thousand miles.


That gas saving feature wouldn't be DI would it?

Nope. It is due to the active fuel management ie dissable 4 cylinders and let the oil that carys over the poorly designed pcv baffle and coke the rings till it uses even more oil mode.

My wife's car is di and doesn't use any oil.


I was looking at your sig line trying to figure it out, thanks!

 

[KrisZ]

If we're talking about excessive oil consumption, like 1 or 2 year old Subaru cars puffing blue smoke upon startup or fairly new cars that need oil topped up between OCI's, then I think the use of very thin oils, gentle break ins and long initial OCIs probably are to blame.

 

[thunderfog]

Originally Posted By: Merkava_4
People get consumption because they're using a thinner oil than necessary.

 

[Chris Meutsch]

Originally Posted By: Merkava_4
People get consumption because they're using a thinner oil than necessary.



Then why do Euro cars burn oil using 40w? Are we advocating a 50w in these?

 

[zach1900]

Originally Posted By: KrisZ
If we're talking about excessive oil consumption, like 1 or 2 year old Subaru cars puffing blue smoke upon startup or fairly new cars that need oil topped up between OCI's, then I think the use of very thin oils, gentle break ins and long initial OCIs probably are to blame.
isn't 1 or 2 year's old still fairly new?

 

[TFB1]

Originally Posted By: Merkava_4
People get consumption because they're using a thinner oil than necessary.


For a engine with all it's clearances in spec, wight of oil makes very little difference...

If it's a burner(more than a qt in 1500-2000mi) because of worn rings/cylinders, no oil or miracle in a can is likely to do more than slightly slow it down... If it's bad valve stem seals, heavier oil will make very little difference, though in some engines high mileage oil or the can miracle may produce significant improvement...

 

[Rand]

Originally Posted By: KrisZ
If we're talking about excessive oil consumption, like 1 or 2 year old Subaru cars puffing blue smoke upon startup or fairly new cars that need oil topped up between OCI's, then I think the use of very thin oils, gentle break ins and long initial OCIs probably are to blame.


I call [censored].
I have yet to see a 1 or 2 year old subaru puff smoke.

the FB25 issue was a small % of engines and even then they wouldnt burn enough to puff.. because it was a ring issue.

Puffing is usually more related to valve guides or other causes.

I did see a subaru wrx sti with broken ring land smoking... but it wasn't 2 years old.

I have actually had 5 of the fb25 powered subarus

2 were long term rental and the other 3 were owned.

Only 1 had an issue and it was a 2013 outback that used

about 1qt per 1500-2300miles

That is STILL not nearly enough to smoke.

It got new rings which didnt totally fix the issue.

It then got a new shortblock.. It now uses 0 oil.

my 2015 forester uses 0 oil.
my 2011 forester used .5qt/3000miles at most.

And the 3 owned fb25 vehicles were all the dreaded
"manual transmission oil burners"

Which makes it out to seem like a majority of the MT equipped vehicles burn oil.

 

[weasley]

Let's not forget that even a perfectly run-in engine with all tolerances in spec and running the correct oil will 'use' oil through volatility - some of the oil simply boils away and escapes out of the crankcase breather.

 

[Chris142]

Ring end gaps.valve guides and low tension rings are 3 reasons

 

[donnyj08]

My vehicles use oil because they have combustion engines which use oil by nature. All combustion engines use "some" oil.

 

[KrisZ]

Originally Posted By: Rand
Originally Posted By: KrisZ
If we're talking about excessive oil consumption, like 1 or 2 year old Subaru cars puffing blue smoke upon startup or fairly new cars that need oil topped up between OCI's, then I think the use of very thin oils, gentle break ins and long initial OCIs probably are to blame.


I call [censored].
I have yet to see a 1 or 2 year old subaru puff smoke.

the FB25 issue was a small % of engines and even then they wouldnt burn enough to puff.. because it was a ring issue.

Puffing is usually more related to valve guides or other causes.

I did see a subaru wrx sti with broken ring land smoking... but it wasn't 2 years old.

I have actually had 5 of the fb25 powered subarus

2 were long term rental and the other 3 were owned.

Only 1 had an issue and it was a 2013 outback that used

about 1qt per 1500-2300miles

That is STILL not nearly enough to smoke.

It got new rings which didnt totally fix the issue.

It then got a new shortblock.. It now uses 0 oil.

my 2015 forester uses 0 oil.
my 2011 forester used .5qt/3000miles at most.

And the 3 owned fb25 vehicles were all the dreaded
"manual transmission oil burners"

Which makes it out to seem like a majority of the MT equipped vehicles burn oil.


Looks like I struck a never here LOL, but it was not my intention to single out Subaru.

Here is where I got my reference from:
http://www.bobistheoilguy.com/forums/ubb...lat/fpart/5/q/1

Originally Posted By: Shark
My brother has a 13 wrx, stock, 30,000 highway miles. Doesn't burn oil but shoots a puff of blue smoke on start up randomly.

I'm on the fence about Subarus. I would not own one with a H6.

 

[lubricatosaurus]

Fundamentally, the cylinders need oil on them for the rings to ride on. Some has to get burned up with the fuel, by design. Beyond that, the responses above nailed it: If a clearances are off by just a little in the valve stems, or the oil control rings are stuck or worn down too much, more oil consumption happens.

This is a careful engineering balancing act in designing low tension rings for fuel economy, and if its off by just a little (due to stuck or semi-stuck rings), more consumption results.