Another "Taxi" Study: Relationship of Engine Bearing Wear and Oil Rheology 872128

[Bill7]

Based on the Taxi and other studies, what is the consensus here - Which oil viscosity has better wear protection: Thinner or thicker oil. I guess there is still the infinite debate. Wish there was one convincing scientific study that could end all doubt and answer this question once and for all.

To give the thin side some credit, I've ridden in so many of those early 2000 to 2010 Ford Crown Victoria V-8 Taxi's with 400,000 miles on them that have used the Ford speced 5W-20 viscosity since new.

I think a vehicle using either 20 or 30 weight oil can each reach 200k/300k/400k miles, but the key question is will using the 30 weight have less engine wear which might translate into less oil consumption. Let's face it, having to add a quart of oil every 1k miles is not a good outcome at any odometer reading.

 

[kschachn]

Engineering better engines and lubrication will always get more efficient. I am curious about the future advancements coming around the corner.

But like I said, the laws of physics won't. It seems to be a common confusion in this particular discussion.

 

[TiGeo]

Last time I checked ... Tribology science, engineering and testing to validate wasn't considered "speculation".

Yes I understand that. You answered my question.

Engineering better engines and lubrication will always get more efficient. I am curious about the future advancements coming around the corner.

I mean warp drives could happen so why not?

 

[ZeeOSix]

Based on the Taxi and other studies, what is the consensus here - Which oil viscosity has better wear protection: Thinner or thicker oil. One word answers only please LOL

A law of Tribology that will never change in any machine that has a lubricant between two moving part is: Thicker oil results in more MOFT which results in less metal-to-metal contact and less wear.

The AF/AW additives in the lubricant is to only mitigate wear when the MOFT doesn't do it's job. MOFT (film thickness) is the main defense against wear, and the AF/AW tribofilm (film strength) is the "back-up" mechanism to mitigate wear when MOFT fails to do so. That's lubrication Tribology in a nutshell.

https://www.machinerylubrication.com/Read/30835/lubricant-film-strength

 

[NismoNVT]

Yes, particularly with anything spec'ing 0W-16 and below due to it being determined that once you got much below the HTHS for an xW-20, that's where issues cropped up.

On the other hand, if you look at how many engines that clearly weren't designed around an xW-20 but were back-spec'd for it and it deemed safe, you can see that this "optimization" wasn't happening to the same degree. Bearing dimension and selection could be the same for two engines of the same family with one spec'ing 5W-20, the other 5W-50, one spec'ing 0W-20, the other 0W-40...etc, based on intended usage profile and "worst case scenario" conditions.

When the thickenss or lack theroff oil disscussion starts, a common theme emerges which is who determines "Acceptable wear" and why do other countries with the same motor have manuals that allow thicker oil?

Any insight based on this study?

 

[ZeeOSix]

When the thickenss or lack theroff oil disscussion starts, a common theme emerges which is who determines "Acceptable wear" and why do other countries with the same motor have manuals that allow thicker oil?

Any insight based on this study?

CAFE drives oil viscosity use in the USA. Even though it may cause more long term wear, it's still "acceptable" by the engine designers. Of course, going thinner than xW-20 has driven new engine engineering and design to run those thinnest oils.

 

[Brian123]

Based on the Taxi and other studies, what is the consensus here - Which oil viscosity has better wear protection: Thinner or thicker oil. I guess there is still the infinite debate. Wish there was one convincing scientific study that could end all doubt and answer this question once and for all.

Good question, maybe another thought from me myself and I does oil temperature come into play here? If you drive the car reasonably and do not see oil temps above 200 degrees then does it really matter?

 

[Bill7]

Based on the Taxi and other studies, what is the consensus here - Which oil viscosity has better wear protection: Thinner or thicker oil.

A law of Tribology that will never change in any machine that has a lubricant between two moving part is: Thicker oil results in more MOFT which results in less metal-to-metal contact and less wear.

The AF/AW additives in the lubricant is to only mitigate wear when the MOFT doesn't do it's job. MOFT (film thickness) is the main defense against wear, and the AF/AW tribofilm (film strength) is the "back-up" mechanism to mitigate wear when MOFT fails to do so. That's lubrication Tribology in a nutshell.

https://www.machinerylubrication.com/Read/30835/lubricant-film-strength

So MOFT (film thickness) will provide less engine wear than additives providing film strength, since if you have sufficient film thickness, then metal on metal contact will never occur, so no need to mitigate metal on metal contact with additives for film strength.

So that means the approach Toyota is taking with 0W-16 oil which doesn't have enough MOFT but compensates with additives for film strength is an inferior solution that will bring about more wear over time.

 

[ZeeOSix]

Good question, maybe another thought from me myself and I does oil temperature come into play here? If you drive the car reasonably and do not see oil temps above 200 degrees then does it really matter?

Yes, oil temperature comes into play. Most newer vehicles have an oil cooler of some kind on it, especially vehicles that are expected to be driven harder, like high performance sports cars and vehicles intended for heavy towing, etc. Keep the oil temps under control and you keep viscosity and MOFT under control. But that doesn't neccisarily mean you can run 0W-8 with oil temps at 200F or less in an engine not designed for 0W-8.

 

[Brian123]

Yes, oil temperature comes into play. Most newer vehicles have an oil cooler of some kind on it, especially vehicles that are expected to be driven harder, like high performance sports cars and vehicles intended for heavy towing, etc. Keep the oil temps under control and you keep viscosity and MOFT under control. But that doesn't neccisarily mean you can run 0W-8 with oil temps at 200F or less in an engine not designed for 0W-8.

Kind of like the Ford Mustang that has the Coyote 5.0 motor that is speced for 5W-20, wait, there is a Track Package with an oil cooler and they spec 5W-50 for the same engine.

 

[ZeeOSix]

So MOFT (film thickness) will provide less engine wear than additives providing film strength, since if you have sufficient film thickness, then metal on metal contact will never occur, so no need to mitigate metal on metal contact with additives for film strength.

So that means the approach Toyota is taking with 0W-16 oil which doesn't have enough MOFT but compensates with additives for film strength is an inferior solution that will bring about more wear over time.

If engine designers and oil formulators could make engines run a very long time on oil with basically zero viscosity (like a HTHS of less than 1 cP) by using special design features, exotic materials and some unicorn AF/AW tribofilm formulation they would in order to squeek that last 0.01% of fuel economy. Basically all the wear mitigation would be by AF/AW tribofilm.

 

[ZeeOSix]

Kind of like the Ford Mustang that has the Coyote 5.0 motor that is speced for 5W-20, wait, there is a Track Package with an oil cooler and they spec 5W-50 for the same engine.

The non Track Pack Coyote also has an oil cooler. The Track Pack also has a bigger radiator which helps keep the coolant-to-oil cooler running more efficiently.

 

[Bill7]

If engine designers and oil formulators could make engines run a very long time on oil with basically zero viscosity (like a HTHS of less than 1 cSt) by using exotic materials and some unicorn AF/AW tribofilm formulation they would in order to squeek that last 0.01% of fuel economy. Basically all the wear mitigation would be by AF/AW tribofilm.

But if we only talk about reducing engine wear (which might result in long term oil consumption), why mitigate metal on metal wear if you can prevent it entirely with higher MOFT. So to simply this discussion, those who prefer oils with higher HTHS numbers want no metal on metal contact, while those on the thin side can tolerate a small amount of metal on metal contact as long as it's mitigated with additives. So it's obvious which is the superior approach. All we need is a thorough and convincing scientific study to answer the thin versus thick debate once and for all and finally get closure on this issue.

 

[Brian123]

The non Track Pack Coyote also has an oil cooler. The Track Pack also has a bigger radiator which helps keep the coolant-to-oil cooler running more efficiently.

Does Fuel Dilution come into play here with this Debate between Thick and Thin?

 

[ZeeOSix]

But if we only talk about reducing engine wear (which might result in long term oil consumption), why mitigate metal on metal wear if you can prevent it completely with higher MOFT.

It's been shown for years in these discussions that more MOFT gives more engine wear protection/headroom. You can take a horse to water but you can't make him drink comes to mind.

AF/AW additives are still very important because there are many engine components that run in the mixed and boundry lubrication realm with involves surfaces rubbing on each other. MOFT helps there, but can't do the majority of the protection like it can in full hydrodynamic lubrication like inside journal bearings.

So to simply this discussion, those who prefer oils with higher HTHS numbers want no metal on metal contact, while those on the thin side can tolerate a small amount of metal on metal contact as long as it's mitigated with additives.

Whatever floats someone's boat ... but my viewpoint is why not add a little wear protection headroom by going a little thicker? I like protecting my investments and I'd rather have the added wear protection than try and see a 0.05 MPG increase in fuel economy.

 

[ZeeOSix]

Does Fuel Dilution come into play here with this Debate between Thick and Thin?

Of course ... doesn't take a lot of fuel dilution to reduce the viscosity and therefore the MOFT. Oils that are already thin (0W-16 and below) with lots of fuel dilution are going to be even thinner.

 

[Bill7]

It's been shown for years in these discussions that more MOFT gives more engine wear protection/headroom. You can take a horse to water but you can't make him drink comes to mind.

AF/AW additives are still very important because there are many engine components that run in the mixed and boundry lubrication realm with involves surfaces rubbing on each other. MOFT helps there, but can't do the majority of the protection like it can in full hydrodynamic lubrication like inside journal bearings.


Whatever floats someone's boat ... but my viewpoint is why not add a little wear protection headroom by going a little thicker? I like protecting my investments and I'd rather have the added wear protection than try an see a 0.05 MPG increase in fuel economy.

Not to go off topic here, but since we're talking about additive packages here for mitigating the metal on metal contact at the points in the engine in the boundary lubrication realm, which oil ingredients would you want more PPM in a Virgin Oil Analysis to get higher film strength? Also, which brand oils provide the best additive package for film strength. Idea might be to choose a high HTHS oil that also has a great film strength additive package so you get maximum film thickness and film strength.

 

[ZeeOSix]

Not to go off topic here, but since we're talking about additive packages here for mitigating the metal on metal contact at the points in the engine in the boundary lubrication realm, which oil ingredients would you want more PPM in a Virgin Oil Analysis to get higher film strength? Also, which brand oils provide the best additive package for film strength.

Sounds like a good topic for a new thread where the debate can turn into "bickering" if no supporting backup info can be given.

 

[Brian123]

Of course ... doesn't take a lot of fuel dilution to reduce the viscosity and therefore the MOFT. Oils that are already thin (0W-16 and below) with lots of fuel dilution are going to be even thinner.

I am so glad you pointed this out, so I will stay with a slightly thicker grade of oil since it will thin down. So, basically, my car is speced for 5W-20 and by using a 5W-30 or 0W-30 during the OCI that oil may turn into a 5W-20? If I start with a 5W-20 oil then with fuel dilution it could turn into a 0W-20?

 

[FishFry]

CAFE drives oil viscosity use in the USA. Even though it may cause more long term wear, it's still "acceptable" by the engine designers. Of course, going thinner than xW-20 has driven new engine engineering and design to run those thinnest oils.

I think we can agree on one thing - if engineers where given free hand to develop the most reliable and efficient (mileage) engine possible, instead of working around government restrictions (emissions requirements etc.) we would get way different engines.
I can't remember one emission restriction related device or development, that didn't hurt mileage, reliability or performance.

It started in California years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. These applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, carbs run fat as a pig, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

Frank