What causes oil consumption to progress, further into the OCI?

[Drew7a]

Consumption is always the lowest for the first 2-3K, then sharply increases.

So when vehicle manufacturers do a consumption test it is generally for the first 1000 miles. If consumption sharply increases after the first 2-3K, then the consumption tests are not accurate.

I have seen this phenomena as well no consumption for the first approx 3K, then 1/2 quart in 500 miles.

 

[SatinSilver]

@kschachn on this one.

 

[DGXR]

Also as the oil level drops there is less oil in the system to absorb heat, suspend contaminants and do the other stuff that oil must do, so the smaller volume of oil is stressed more.

 

[paulri]

That explanation is easy to see how it could happen.

Also as the oil level drops there is less oil in the system to absorb heat, suspend contaminants and do the other stuff that oil must do, so the smaller volume of oil is stressed more.

 

[mahanddeem]

My experience is the opposite. I have seen faster "burning oil" in the 1st 1.5k to 2k period of OCIs in the Nissan engines.

 

[Sedin26]

In my CR-V I’ve found I’m down a quart at 1500km with 0w20, at 2500km with 5w30, and it takes about 4000km to be down a quart with 5w40, all within the same brand and family of oils.

 

[paulri]

Well I've replaced the PCV in all three cars, and it doesn't appear to have had an impact on oil consumption, although I'll have to wait out the OCIs to beyond 3K to know for sure. But my next step is thicker oil. Unfortunately I bought a ton of 20 grade oil online ultra cheap, so it might take me a while. I'm going to mix in some 50 grade synthetic to thicken it up some, before then.

In my CR-V I’ve found I’m down a quart at 1500km with 0w20, at 2500km with 5w30, and it takes about 4000km to be down a quart with 5w40, all within the same brand and family of oils.

 

[PontiacHO]

Combustion byproducts, such as fuel, moisture, soot, etc.

Just a guess, I could be completely off base.

Yes. As the oil is older it’s thinner due to the contamination and begins to speed up the consumption. Easier then to get past the rings and valve guides. For cars that use oil quicker right after oil change and brought to “capacity “ it’s usually caused by windage of the internals turning it into mist getting past the rings and/or collected by the PCV system.

 

[Pablo]

Yes, indeed. As the minute materials escape past the rings, inevitably some oil escapes as well.

 

[doublebase]

I always assumed it was because of dilution of fuel or shearing. But I don’t know.

All I know is that I had one particular car where it was very noticeable. A Lexus LS460. Up to 4,000 miles it would appear to use nothing, not a drop...then when it reached 5,000 miles, BOOM. It would use a quart every 1,000 miles on the way to 7,000 miles. And then I’d change it. I experienced something similar in my 2018 Silverado.

I’m not sure why it happens - but I can tell you why it happens with brake pads - with pads the first half of the pads life will last longer than the second half, because of the thickness. The thickness of the original pads dissipates heat better, whereas the worn pads can’t, and will wear much faster because of what it no longer has (material thickness). Next thing you know, you’re metal to metal on the rotor. You thought you had as much time as the first however miles you put on those pads, but you don’t.

 

[weasley]

Also as the oil level drops there is less oil in the system to absorb heat, suspend contaminants and do the other stuff that oil must do, so the smaller volume of oil is stressed more.

This. It's why I always recommend to top up little and often, rather than wait until the level reaches "Min".

 

[Stumpy]

Back in the early '80s Consumer Reports magazine tested in Mercedes-Benz. I believe it was a 190. They noted what they called excessive oil consumption and they contacted Mercedes about it. Mercedes in typical German fashion sent them a letter stating that all properly engineered engines would consume oil the harder they were run and they asked if this oil consumption happened or was noticed directly after their acceleration and performance testing. Consumer Reports stated that was when they noticed that the oil was low in that the car and it did not consume any more oil under normal driving conditions.