is 0W-20 always better for mpg than 5W-20?

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I just read the Motor oil 101 to 109 here on BITOG and if I understood correctly what he was saying, it seemed to me that he was saying that all motor oils were actually too thick at room temperature to give optimal lubrication and optimal mpg at initial start up but that 0W oils were thinner than others and thus minimized the problem. So, my question is for a 2014 Kia Forte 2.0 GDI which recommends 5W-20 or 5W-30, if I'm not doing any abusive driving or high speed driving in Arizona during the summer, would 0W-20 and 0W-30 be better choices if my goal is to achieve the highest fuel economy? Am seriously thinking about the Toyota 0W-20 as it seems to have gotten rave reviews here on BITOG and other places. On the other hand, I don't want to jeopardize the warranty either, especially if using the 0W-20 is not going to make a meaningful difference in mpg. What are people's thoughts here about this? This vehicle only has 2300 miles on it and am just about to do my first oil change. Thanks in advance for the input.
 
I doubt the mileage increase will be anything you could put your finger on.

We also do not know what Kia knows about 0/20 in their motors that we do not. I suspect that they just did not consider them, when making the specification, but it is a new car, and you really do not have a lot to gain but going outside the manufacturer's specs.....JMHO.
 
The only difference between those 2 grades will be at start up,and only once the ambient temps get into the negatives,so for your Arizona conditions there will be no meaningful difference so pick a 5w-20 grade in the flavour you like best,or what's on sale and call er done
 
I doubt your 2014 Kia Forte 2.0 GDI calls for a 5W30. I'm sure the required oil is 0W20 or 5W20 and using a 0W in place of 5W will not void your warranty.
 
I just double checked the owner's manual and 5W-20 and 5W-30 are both recommended for all temperatures. Surprisingly, it even says 10W-30 is okay for temperatures of 0 fahrenheit and above.
 
Originally Posted By: Jasper8146
I just double checked the owner's manual and 5W-20 and 5W-30 are both recommended for all temperatures. Surprisingly, it even says 10W-30 is okay for temperatures of 0 fahrenheit and above.


You will see a bigger difference in mileage (Although still very small) between 5/30 and 5/20 than you will between 5/20 and 0/20.
 
Amsoil site says 5w20 or 5w30 at all temps but 5/20 is preferred, & 10w30 ok above 0*f
Using a 0 grade instead of 5 won't make much MPG gains, but I feel most useful in winter months for cold starts.
 
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Originally Posted By: Jasper8146
I just read the Motor oil 101 to 109 here on BITOG and if I understood correctly what he was saying, it seemed to me that he was saying that all motor oils were actually too thick at room temperature to give optimal lubrication and optimal mpg at initial start up but that 0W oils were thinner than others and thus minimized the problem.

That makes sense, good advice. Look at it this way, the "perfect" oil-of-the-future will not get much thicker when cold and not thin out when hot, same viscosity all the time. We can't do that with current technology, but we can get closer to that when we use a 0W-20.

Originally Posted By: Jasper8146
So, my question is for a 2014 Kia Forte 2.0 GDI which recommends 5W-20 or 5W-30, if I'm not doing any abusive driving or high speed driving in Arizona during the summer, would 0W-20 and 0W-30 be better choices if my goal is to achieve the highest fuel economy? Am seriously thinking about the Toyota 0W-20 as it seems to have gotten rave reviews here on BITOG and other places. On the other hand, I don't want to jeopardize the warranty either, especially if using the 0W-20 is not going to make a meaningful difference in mpg. What are people's thoughts here about this? This vehicle only has 2300 miles on it and am just about to do my first oil change. Thanks in advance for the input.


Like others have said, there is a small fuel economy advantage to using a 0W-20. Small. Anyway, we have had similar discussions about durability of engines using a 20 vs. 30 (or 40), and, to me, this sums it up: http://priuschat.com/attachments/fuel-efficient-motor-oil-technical-article-pdf.11772/ I don't think a 20 is a durability problem, and just looking at the Stribeck Curve convinces me the Shell tribologists are right, saying no problem.
 
Originally Posted By: FetchFar
and just looking at the Stribeck Curve convinces me the Shell tribologists are right, saying no problem.


Can you explain how you look at the Streibeck curve, without knowing either the geometry or the applied load ?

Bottom axis is (operational viscosity x surface speed / applied load).

Unless you know those, you can't read the Streibeck curve.

Unless I'm missing something and there's another way.
 
Originally Posted By: Shannow
Bottom axis is (operational viscosity x surface speed / applied load.


Not "load", its actually pressure. Thats load per unit area, maybe thats where the missing geometry you mention comes from. Therefore, more surface area means a thicker oil film, all other things (visc, speed) being equal.
 
Originally Posted By: Shannow
Can you explain how you look at the Streibeck curve, without knowing either the geometry or the applied load ?


I discussed this before on these forums in more detail, but, essentially, the bearing engineer knows the worst-case load force (max torque), at a low rpm (lugging), and knows what viscosity oil he wants to use, and then he determines the bearing surface area that will give minimum friction on the Stribeck Curve plus some margin to allow for normal viscosity drops with oil ageing (fuel dilution, VI degradation, etc.). A good choice would be a Stribeck Curve choice of 0.4 on the http://www.stle.org/resources/lubelearn/lubrication/ chart, near minimum friction, yet allows for less viscosity should it occur. .... Now notice the small difference between a 30 oil vs. a 20 oil, and notice that using the thinner oil really doesn't move you to the left on the Stribeck Curve much at all (notice log scale).
 
I'm fairly familiar with the curve, and that the applied load is pressure...how do you know what the applied load (pressure) IS for the different geometries and families of engines ?

...and therefore where on the curve that you are when stating that 20s are right ?

You also need to get the right curve that includes the extensi0n off to the left for friction modified boundary conditions, because as per the paper you linked a few posts back, engines are increasingly operating way off to the left of the chart (which, yes, is logarithmic)
 
Originally Posted By: FetchFar
A good choice would be a Stribeck Curve choice of 0.4 on the http://www.stle.org/resources/lubelearn/lubrication/ chart, near minimum friction, yet allows for less viscosity should it occur. ..


The designer would choose the point on the Stribeck Curve FIRST, probably a 0.4 since its just to the right of the friction minimum. ... A second step would be to plug in the desired oil viscosity to use (say a 30), and then to pick a high torque and low rpm case that is worst-case (depends on engine power/torque curves. All that is left is bearing area, something the designer has original control of, a design variable.

Originally Posted By: Shannow
..how do you know what the applied load (pressure) IS for the different geometries and families of engines ?
...and therefore where on the curve that you are when stating that 20s are right ?


The designer already knows the Stribeck Curve point for the particular engine to start with, and he knows the power/torque curves for an engine worst-case, and assume he has also already chosen a 30 oil to get there. Now, a 20 oil has about 10% to 20% less viscosity than a 30, so it actually slides it to the left a bit, but not much as we see on the curve, so we are still hydrodynamic.

Originally Posted By: Shannow
You also need to get the right curve that includes the extensi0n off to the left for friction modified boundary conditions, because as per the paper you linked a few posts back, engines are increasingly operating way off to the left of the chart (which, yes, is logarithmic)
..... As for the left part of the curve, thats in a mixed-boundary lubrication all the way to near-zero, so we almost totally depend on the anti-wear additives to save bearings from destruction there, nothing more can be done, like on start-up in crank/pin bearings, or on cam lobes full time, timing chain pin/links, etc....
 
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OK...your point is...

Designers know their stuff, and pick a point in the "safe" hydrodynamic range. Designers, knowing your stuff add a safety margin.

So you can install (and advise others) to install a thinner oil.

Problem is, it's not your reading, or analysis of the Streibeck curve (whether it's logarithmic, in pressure units or other), you are simply guessing that it's somewhere, and guessing that changing the oil viscosity moves it somewhere else, and guessing that place is OK.

Except that means that they LOSE their designer installed safety margin, for all of 0.4% improvement in fuel economy (figure 13 of your linked document....and it's a GUESS, pure and simple...not scientific analysis, regardless of the big words.

As to

Originally Posted By: FetchFar
..... As for the left part of the curve, thats in a mixed-boundary lubrication all the way to near-zero, so we almost totally depend on the anti-wear additives to save bearings from destruction there, nothing more can be done, like on start-up in crank/pin bearings, or on cam lobes full time, timing chain pin/links, etc....


With the increases in fuel economy requirements, all of the manufacturers (Honda, Ford, etc.) are telling us that they are operating in boundary mode more and more often, and that the new standards require new and better friction modifiers to provide adequate protection under those conditions...was discussed before here

http://www.infineum.com/sitecollectiondocuments/notebooks/gf5/ResearchReport.pdf

Page 78 or thereabouts.

So if you "guess" that the designers know their job, "guess" that they are all in the hydrodynamic range (probably an incorrect "guess" these days), and "guess" that moving to the left is still in hydrodynamic range, your guesses could be disastrous.

Repeat...modern engines are operating already in mixed mode/boundary for improved fuel efficiency. They are telling us this in their literature, and the test engines that they are electing for their standards.
 
Originally Posted By: Shannow
OK...your point is...Designers know their stuff, and pick a point in the "safe" hydrodynamic range. Designers, knowing your stuff add a safety margin.

Good, we agree on that.

Originally Posted By: Shannow
So you can install (and advise others) to install a thinner oil.

Mostly based on Shell's study at http://priuschat.com/attachments/fuel-efficient-motor-oil-technical-article-pdf.11772/ which I'll quote below.

Originally Posted By: Shannow
Problem is, it's not your reading, or analysis of the Streibeck curve (whether it's logarithmic, in pressure units or other), you are simply guessing that it's somewhere, and guessing that changing the oil viscosity moves it somewhere else, and guessing that place is OK.

You can easily put in 8 cs vs. 10 cs (going from a 20 to a 30 oil) into the ZN/P relationship and shift the curve in http://www.stle.org/resources/lubelearn/lubrication/ .
And yes, any design engineer would place it around 0.4 (maybe upwards of 1). Put 8 cs in instead of 10 cs (again, 20 vs. 30), worst case moves the 0.4 to 0.3 ---> Not much movement on the Stribeck, obviously. The point.

Originally Posted By: Shannow
Except that means that they LOSE their designer installed safety margin,...

The discussion was, in going from a 30 to a 20 weight, and we see that only moves the Stribeck a small amount. Emphasis on SMALL amount. Very little margin lost.


Originally Posted By: FetchFar
..... As for the left part of the curve, thats in a mixed-boundary lubrication all the way to near-zero, so we almost totally depend on the anti-wear additives to save bearings from destruction there, nothing more can be done, like on start-up in crank/pin bearings, or on cam lobes full time, timing chain pin/links, etc....


Originally Posted By: Shannow
With the increases in fuel economy requirements, all of the manufacturers (Honda, Ford, etc.) are telling us that they are operating in boundary mode more and more often, and that the new standards require new and better friction modifiers to provide adequate protection under those conditions...was discussed before here
http://www.infineum.com/sitecollectiondocuments/notebooks/gf5/ResearchReport.pdf
Page 78 or thereabouts.


Thats a pseudo-ZN/P, for the entire engine, for discussion purposes. The ZN/P for the crank journal bearings SPECIFICALLY remain hydrodynamic for running conditions, a very important point to remember. Its well known that the valvetrain, timing chain, rings, operate in mixed-boundary conditions, always have and always will.

Originally Posted By: Shannow
So if you "guess" that the designers know their job......


They do know their job, not a guess. The same people I observed in Mechanical Engineering school & the SAE who did this specific task are sharp people, no doubt.

End of discussion for me. I'll just let the "Improved Fuel Efficiency by Lubricant Design : A Review by R.I. Taylor & R.C. Coy, Shell Research & Technology Centre, Thornton, United Kingdom paper take it from here. Address all questions to Shell from now on please. LOL...
"In our laboratory, it has been observed that in a modern gasoline engine, well designed
automotive bearings can be lubricated with oils as thin as 2.3 mPa.s (and a 20 weight oil has 2.6 to 2.9 mPas) without any observable wear on either con-rod or main bearings.
The assumption that lower viscosity lubricants automatically give rise to thinner oil films in key lubricated contacts in a gasoline engine is also open to question, particularly in the case of piston rings. Laser Induced Fluorescence measurements have found that, in a Nissan gasoline engine, the mid-stroke top ring oil film thickness was greater for an SAE-5W/20 lubricant than it was for an SAE-15W/40 lubricant. "
 
Jasper8146, as others have mentioned, your car is spec'd for the 5W-20 grade so in a warranty situation it is possible that you could be questioned as to why you're using a 0W-20.
Now if you're not concerned with that then yes you can use a 0W-20 and even the TGMO 0W-20 as a number of Hyundai/kia owners have with good UOA results. But be advised that TGMO is one of lightest 20 grade oils available so in your climate, since your car is not equipped with oil gauges to monitor things I'd suggest substituting a 1/2-1 quart of M1 0W-40 to give your a somewhat heavier 0W-20 oil. It will still be lighter on start-up than all 5W-20s and even most aftermarket 0W-20s, but it will retain a higher high temp' viscosity.
 
what does car manufacturer know that we don't?that one is easy,when their car get reviewed they know the reviewer will say how much per year in maintenance the car will cost so the more inexpensive the better ,yep you guessed it some manufacturer went too far a long time ago lol!
 
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