Friction or hydrodynamic lubrication

[ka9mnx]

I have been visiting this topic in my head for many years.

If I could run an engine in a hypothetical lab condition eliminating outside influences such as road conditions, terrain, humidity, temperature, wind, drag, etc. With these parameters set, I record fuel economy over a range of engine loads and speeds with oil "x". Now, with oil x completely flushed, I now run oil "y". Oil y shows an average MPG better than oil x.

Would the increase of average MPG of oil y be due to the oils reduction of mechanical friction in the engine or the reduced hydrodynamic drag of the oil? Or would both contribute.

Facts please. No speculation please. References to publications would be extremely helpful.

 

[ABN_CBT_ENGR]

Originally Posted by ka9mnx
I have been visiting this topic in my head for many years.

If I could run an engine in a hypothetical lab condition eliminating outside influences such as road conditions, terrain, humidity, temperature, wind, drag, etc.

Oil y shows an average MPG better than oil x.

Would the increase of average MPG of oil y be due to the oils reduction of mechanical friction in the engine or the reduced hydrodynamic drag of the oil? Or would both contribute.

Facts please. No speculation please. References to publications would be extremely helpful.


I do this a good bit so I'll address it and the authority is the conservation of energy

By your standards where all parameters were 100% identical and equal at all ranges

If a difference occurred from the oil only- then the only mode could be a relative property that only the oil directly influences.

That would be friction from 2 body contact created the "delta"

( assuming no particulate presence to grind and change clearance or finish since this is hypothetical) That can only come from

Dimensional increase from a change in heat removal ( thermal growth)

Increase in film strength

Here's the potential paradox

If nothing else changed- it would not be possible for the other oil to achieve either because the potential energy to allow for those alterations would not exist because it was never introduced. ( if no operating parameter changed then it would not present a circumstance to take advantage of any other oil property even if it was present)

So even if the simple concept of cause/effect is employed and oil "X" achieves a performance value of "1"- oil "Y" could not exceed "1" ( it could be argued that it could achieve less than 1) unless something else changed which was not allowed due to the constraints you imposed in your model.

 

[ka9mnx]

Excellent! Thank you...

 

[Gokhan]

https://www.bobistheoilguy.com/foru...6/re-0w-8-is-here-jaso-glv-1#Post5444956

 

[ZeeOSix]

Originally Posted by ka9mnx
Would the increase of average MPG of oil y be due to the oils reduction of mechanical friction in the engine or the reduced hydrodynamic drag of the oil? Or would both contribute.


Both would contribute if oil x and y were different viscosity because of the difference in oil shear drag between parts - that's the main reason that xW-20 is recommended by most manufacturers over xW-30 to get a little more gas mileage for CAFE credits.

And there may be more friction due to more metal-to-metal contact (surface asperities contact, mainly in the boundary and mixed lubrication realms) if one oil was much thinner than the other, and the level of friction when that happens would depend on the anti-friction additives in the oil.

In full hydrodynamic lubrication in journal bearings, it's mainly the oil shear drag due to viscosity that plays the main role, but if the viscosity becomes too thin then the MOFT can become too small to prevent metal-to-metal contact.

 

[ka9mnx]

Thanks and that is exactly how I envision what's happening. I recently changed my Ranger from 5w-30 to 0w-20. I wasn't expecting much change but the engine feels like it revs easier before warm up (Kv@40C). Verdict is still out on MPG but I'm expecting to see a slight up tick in MPG (modern additives) after what I'm experiencing now pre warm up.