Correlation between oil volume and OCI

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A bigger sump allows manufactures to run lighter oils and keep viscosity in check at the same time. More oil contributes to lower temps.
 
Big sump BMWs have coolant-to-oil heat exchangers that try to warm up the oil when its colder than the coolant, and of course cool the oil when it gets hotter than the coolant. So the temperature gets adjusted on some vehicles.
 
^^^Yep, even my new Ram has one for both the trans and the engine oils.
It's just as much for warm up as cool down.

And the OP's question is extremely platform specific and controlled by duty cycle. So an all highway miles guy with a long commute is going to need different OCI's than a short tripper, with sump size only allowing a variance based on usage.

Those who simply choose a ridiculous interval and claim immunity to the demands of good maintenance are just choosing not to care...
 
There is a relationship for sure, but there is a lot more to the OCI than just the sump size. European cars are all bad examples because they require oils that meet their extended drain interval specifications.

Plus, I think that having a large oil sump is actually detrimental in the cold winter months or for short trips around town, as more oil will take longer to heat and the larger sump will accumulate more moisture.

Large sumps, on the other hand, are very good for vehicles that operate long hours or at high RPM. More oil means more stable temperatures and of course more capacity to deal with contaminants, hence longer OCI.

In the end it is a balancing act. Both small and large sumps have their advantages and disadvantages depending on the vehicle and the duty cycle.
 
Originally Posted By: SteveSRT8
And the OP's question is extremely platform specific and controlled by duty cycle.


It's actually the opposite, at least the way I intended it. I tried to write my question to be independent of other variables. I know that a lot of factors go into determining an OCI. I'm interested in the oil volume factor alone.

Originally Posted By: 147_Grain
A bigger sump...More oil contributes to lower temps.


This is sort of where I'm going with it. Let's make it easy: let's say you double the oil capacity, from 5 quarts to 10 quarts. If you add 100% more oil volume then, in concept, each unit of oil travels though the engine half as often, right? The oil stays cooler, which is a good thing. But the additives would also be used up at a slower rate. Is this a 1-to-1 correlation? Would going from a 4-quart to a 5-quart sump mean that volume of oil would last 20% longer?
 
Sump volume will be somewhat proportional to the displacement and number of cylinders of the engine. So I feel sump volume won't play a big role unless the car has an unusually small or large sump for the engine size.
 
Originally Posted By: Hokiefyd
Originally Posted By: SteveSRT8
And the OP's question is extremely platform specific and controlled by duty cycle.


It's actually the opposite, at least the way I intended it. I tried to write my question to be independent of other variables. I know that a lot of factors go into determining an OCI. I'm interested in the oil volume factor alone.


The problem is you are over simplifying the question which means a real answer must be qualified.

If you ignore all other variables then of course it is a linear relationship to volume. But that is not relative to any real world usage...
 
The time the oil is resting in the sump is time it isn't being oxidized or depleted--the oil pump is pumping the same gallons per minute regardless of the sump size. Double the sump size, double the resting time, double the OCI. Yes, warming in cold weather is a concern.
 
Originally Posted By: SteveSRT8

If you ignore all other variables then of course it is a linear relationship to volume. But that is not relative to any real world usage...


Some aspects of oil depletion are not linear. TBN, for example, does not reduce at a linear rate. I was thinking that as you reduce the oil volume, your target OCI might actually go down faster than your reduction in volume (a non-linear relationship) because of secondary or tertiary side effects from the smaller volume. For example, the faster additive depletion from the reduction in volume alone might be compounded by the increase in temperature that the smaller volume of oil might suffer, depleting the oil even sooner.

Sort of like an economy of scale thing.
 
my .02
my 92 TA 5.7L took 5 qts...3k OCI
my '14 Focus ST 2.0T takes 5.7 qts...3k OCI
Why?
The TA manual called for 3k OCI (I fell under severe schedule) while,
The Focus puts way more stress on the oil than the TA did even with almost 1 more qt of oil.
+Volume can lead to greater OCI...if conditions allow.
My advice...follow the manual, that's why it came with one.
 
Last edited:
Originally Posted By: tojo1968
my .02
my 92 TA 5.7L took 5 qts...3k OCI
my '14 Focus ST 2.0T takes 5.7 qts...3k OCI
Why?
The TA manual called for 3k OCI (I fell under severe schedule) while,
The Focus puts way more stress on the oil than the TA did even with almost 1 more qt of oil.
+Volume can lead to greater OCI...if conditions allow.
My advice...follow the manual, that's why it came with one.


Wow. Only 3k in the ST? I bet they don't spec that in Europe.
 
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