How does blowby gas increase oil consumption?

[Fordiesel69]

I keep reading that blowby is one of the bigger causes of oil consumption. I'm wondering how--if it is merely gas (vapor, not fuel) that dissolves into the oil, how would it make the vehicle consume more oil? FWIW, in my last UOA, I noticed about 1.5 quarts of oil consumption (5 quart sump, 5000 mi OCI) and the viscosity was still in grade for 20 grade, so I don't think anything was thinning the oil. The piston ring factor as a cause of consumption makes sense to me, but not blowby gas. Can someone explain in basic terms?

So this is my observation on the engines I have torn down. Blowby is caused by the piston rings not being able to seal onto the cylinder wall for one reason or another. Now having said that, in all cases that I have seen the oil ring is worn pretty much equally with the upper compression rings. So the increase oil consumption is not solely due to blowby but because blowby and ring wear go hand in hand.

This can also be the case for low spring tension on the rings when it comes to low friction piston rings. GM uses a lot of low tension rings on their 4 and 6 cyl engines, and upon a tear down they may not be worn. They are just incapable maintaining their interface with the cylinder walls. A hone / deglaze and a new set of rings will correct the issue assuming the engine was maintained.

 

[weaponoffreedom]

Worn control rings cause blow-by and oil consumption. ?However some engines have low tension rings and consequently consume more oil than a typical engine.

whuch adds no advantage to an engine whatso ever I would add.

 

[PontiacHO]

Blow by is the result of degrading ring seal. This is the reason for increased oil consumption It’s not the blow by that is the cause. It’s worn/poor rings/seal.

 

[weaponoffreedom]

Blow by is the result of degrading ring seal. This is the reason for increased oil consumption It’s not the blow by that is the cause. It’s worn/poor rings/seal.

unless you are talking about these new engines

 

[PontiacHO]

Not sure what you are referring to…
Blow by is compression escaping past the rings.
Did I misunderstand the original question?

 

[Shel_B]

Piston Rings and Blowby
Might be helpful to this discussion

 

[flash7210]

Not sure what you are referring to…
Blow by is compression escaping past the rings.
Did I misunderstand the original question?

And combustion gases/vapors

This includes unburnt fuel and water vapor

 

[PontiacHO]

That’s a given…

 

[chris719]

Meh, I'm at a 175k miles in my Mazda3. At least during my ownership the past 107k miles, it's been 0W20 and I still have zero perceptible consumption between 6k-7.5k OCIs.


If it were 0W20, wouldn't everyone have appreciable losses during such an OCI?

Yes, I have a 2.5 MZR with 159k that’s seen 0W-20 almost exclusively and burns just about nothing. It’s the engines that matter.