The Great Filter Debate

[Bror Jace]

Yes, the oil life monitors (OLMs) use a fairly sophisticated algorithm to monitor the amount of wear on an oil from a variety of inputs including number of stops and starts, length of trips, total miles, maybe even ambient temps during the interval. Ahead of time they project what effect that will have on wear (they don't adjust for the type of oil you use, obviously) and try to get people to change their oil before a significant amount of damage is done.

I once saw a Civic owner that ran is oil until the minute the OLM said 0% ... he then changed the oil and sent the sample away for a UOA. The oil was completely shot and there were blatant signs of increased wear.

So, they are a tool ... and like a lot of tools in our everyday lives, they are dumbed down to the lowest common denominator. Following them is not necessarily the smartest way to go. Keep this in mind when looking at the OLM.

And no UOA I've ever seen is able to measure the coefficient of friction of oils. I've seen some manufacturer testing (I think it was from Red Line) and I was aghast at the drop across the board among all brands ... and the oils were not in use all that long.

Interesting about BMW using electrical properties. I'm not sure what conductivity oil has (I'm assumin it's poor) but it does make sense that as it accumulates moisture and acids, that value would change (increase) and that seems like a pretty good input as to the condition of the oil for an OLM.

Of course, I think that by this time the oil is well on its way to being shot so I'd want to change it before those properties change enough to register (of course I'm just guessing about the meter's sensitivity).

Because I travel about 9,000-10,000 miles per year and don't want to have to change my oil in the middle of winter, I end up changing my oil every 3,500 miles or so. Even if I went up to 15,000+ miles per year (which is what I used to do) I'd probably keep the same schedule.

For a lot of short trips (12-15 minute commute one way) that isn't too excessive and I diligently take my oil back for recycling, of course.

[trebuchet03]

Originally Posted by Bror Jace

And no UOA I've ever seen is able to measure the coefficient of friction of oils. I've seen some manufacturer testing (I think it was from Red Line) and I was aghast at the drop across the board among all brands ... and the oils were not in use all that long.

Viscosity is a measure of fluid resistance, which can be thought of as friction In any case (as internal resistance isn't what you're talking about ), friction coefficients are not the metric used (at least in the report's I've received) to determine when a oil starts to become abrasive, actually knowing these values would be purely academic.

Really, I don't see how one would measure the friction coefficient - that's going to be dependent on the individual parts (materials, surface condition, etc.) and their load conditions on top of the state of the oil. I guess one could make a standardized test, but those figures would again, be purely academic and, in this case, not directly applicable (compared to metrics such as TBN, insolubles, elemental makeup, etc.).

[Bror Jace]

Trebuchet03, the resistance to a heavier fluid is hydrodynamic drag. Since the engine parts push the oil out of the way as it turns, the heavier (greater resistance to flow) the oil, the greater resistance for the engine ... otherwise known as higher load.

Coefficient of friction is different. They must use fluids of equal weight (cSt - centistrokes) and then rub one surface against another (say, a small polished metal plate against a larger flat surface) and then measure the resistance.

That's just a guess ... but some SAE-type tests are actually that simple. Ever see a Timken bearing machine used in oil tests?

[trebuchet03]

Originally Posted by Bror Jace

Trebuchet03, the resistance to a heavier fluid is hydrodynamic drag. Since the engine parts push the oil out of the way as it turns, the heavier (greater resistance to flow) the oil, the greater resistance for the engine ... otherwise known as higher load.

Coefficient of friction is different. They must use fluids of equal weight (cSt - centistrokes) and then rub one surface against another (say, a small polished metal plate against a larger flat surface) and then measure the resistance.

That's just a guess ... but some SAE-type tests are actually that simple. Ever see a Timken bearing machine used in oil tests?

That's all well and good - but I stand by my original statement

...friction goes up as contaminates accumulate and additive packages deplete... But to say my long oil change interval = accumulated bits and depleted additive packages is a fallacy.

As for the timken OK load test machine - yes, there's one (well, probably more than one that I'm unaware of) @ my school's shop. But, it's a qualitative-relative test. I'd get slapped (and/or, a good talking to ) if I reported the results at face value rather than comparing one sample to another one. There are much better quantitative-discrete tests which are used

[flydude1221]

Originally Posted by Bror Jace

Trebuchet03, the resistance to a heavier fluid is hydrodynamic drag. Since the engine parts push the oil out of the way as it turns, the heavier (greater resistance to flow) the oil, the greater resistance for the engine ... otherwise known as higher load.

This is why all manufacturers have switched to 5w20 weight oil as the lower engine load improves fuel economy which inturn makes a manufacturers average fuel efficiency for all vehicles produced higher.

[Bror Jace]

Yes flydude, that is correct. The thinner oils are almost always introduced to save fuel. Funny thing is, 5W-20 oils also protect as well as 5W-30 oils (proven by UOAs).

Trebuchet03, you implied above that viscosity = friction. I was trying to separate the two. I'm sorry if I was not clear.

[flydude1221]

I did not think that a 5w20 would protect as well as a 5w30. Interesting, perhaps I will run some 5w20 in my vx.

[Bror Jace]

Yes, using a thinner (not necessarily synthetic) oil (5W-20, 0W-20, etc ...) will provide less drag/resistance and possibly improve fuel economy by a measurable amount.

Most cars that currently spec 5W-20 were designed with 5W-30 in mind. So, it stands to reason that many engines that currently spec 5W-30 can be switched over with no adverse effects ... just a slight increase (0.25 - 0.50) in measured fuel economy. If you search the UOA section of BITOG, you can find others that have already gone this route and had a sample tested for signs of increased wear. I haven't seen all these results, but I have yet

There are two other factors that make me comfortable with this idea:

1) With any interval past 3,000 miles, most XW-30 oils shear down to a XW-20 anyway. With the extended intervals recommended by most manufacturers these days, many engines are operating with a 20 weight oil in the sump.

2) When some manufacturers (Ford and Honda come to mind) switched over to 5W-20, they made sure the oils were made with more Group II+ or Group III base stocks for added stability and they increased the barrier anti-wear additives such as moly and boron. UOAs of these 5W-20s show this clearly.

Now that ZDDP levels in SJ, SL, SM oils are lower than their predecessors, the blenders have discovered that adding moly and/or boron can make a very high-performance, low-wear oil.