One more bite at the 5w20 v. 5w30 debate:

[Gokhan]

Originally Posted by ZeeOSix
You have to look at the curve fit of the data, not individual data points.

Be careful when you curve-fit with only four data points, especially when other variables -- base-oil viscosity in this case -- are likely not fixed.

 

[KevinP]

Originally Posted by Gokhan
Originally Posted by ZeeOSix
Originally Posted by Gokhan
What I like about 5W-20 is that it uses a thicker base oil than 5W-30 does. So, while the HTHS viscosity, which is relevant to the wear protection of the bearings, is a little less, the valvetrain, timing chain, and rings and liners will have less wear with 5W-20 than with 5w-30 because the base oil is thicker.

Not so sure about that. There's been quite a few papers that show less wear on most engine parts with higher HTHS viscosity. Looks like when the HTHS starts going below 2.6 cP is when the wear really starts to increase. Most xW-20 weight oils have a HTHS around 2.6~2.7 cP ... so basically they are starting out real close to the point on the graph where the wear starts increasing noticeably - so what happens with a lot of fuel dilution and/or oil shearing to decrease the viscosity even further?. Also, higher RPM has a big effect on ring wear ... so cruising around like a grandpa will result in less wear.

Let's not read too much into one plot, especially with no additional info on the test oils having been provided.

If you look at the plot, HTHS viscosity = 2.6 cP is producing the least ring wear -- the effect being drastic at 3000 rpm and 6000 rpm -- at virtually all rpms. So, perhaps this oil has a thicker base oil than the 3.1 cP oil.

We have no information on the 2.2 cP and 2.4 cP oils -- they may also be using very thin base oils as well. Therefore, we don't know if the rise in the wear is because of the fall in the HTHS viscosity or the fall in the base-oil viscosity.


I'd be interested in the mechanism for increased wear in timing chain/valve train, based upon your base oil explanation. Why does the 20W perform better?

 

[Gokhan]

Originally Posted by KevinP
I'd be interested in the mechanism for increased wear in timing chain/valve train, based upon your base oil explanation. Why does the 20W perform better?

HTHS viscosity is measured at a shear rate of 1,000,000 1/second. Shear rates at the valvetrain and timing chain are over 10,000,000 - 100,000,000 1/second and the VII polymer molecules get fully aligned against the flow in such extreme shear rates and no longer contribute to the viscosity, reducing the viscosity to the viscosity of the base oil and additive package.

https://www.bobistheoilguy.com/foru...y-hthsv-friction-and-wear-state-of-the-a

 

[ZeeOSix]

Originally Posted by KevinP
Why does the 20W perform better?


I really don't see a 20W performing better in that ring wear graph since most xW-20 oils have a HTHS viscosity of around 2.6 cP, which is where the wear rate starts to noticeably increase at a given engine RPM. And engine RPM was part of the variables in that graph data, so it's a reflection of the higher shearing rates and heat in the ring area associated with increased engine RPM. From what I've been gathering, it seems rings take a lot of abuse because of the high oil shearing rates, and also because the oil gets very hot and thins down even more in the ring pack area.

As far as timing chain/valve train wear ... I'd like to see some real life engine test data of the HTHS vs timing chain/valve train wear rates. And the only way to see the sole effect of only the viscosity would be to have different oils with the same exact anti-friction/anti-wear formulation since those play a big roll in controlling wear in timing chain/valve train components.

 

[ZeeOSix]

Forgot to mention that xW-20 is mostly adequate and works fine on every day, light duty vehicles that aren't pushed hard for long periods of time. In an engine where there's lots of continuous high RPM and high loads/heat, a thicker oil is going to give more engine wear protection headroom (higher HTHS, higher MOFT between parts).

IMO, xW-20 is on the borderline of being a bit thin (HTHS of ~2.6 cP) to give much room for heavy engine use (turboed, heavy towing, continuous high speed driving, track use, fuel dilution in GDI engines, etc). Driving around in a normal benign manner where RPM is low or only short durations of high RPM, and keeping oil temps below 225F, then xW-20 will be work fine. Some people still bump up to a 5W-30 just to give that added wear protection headroom buffer, regardless of their driving habits/conditions.

 

[demarpaint]

Originally Posted by ZeeOSix
Forgot to mention that xW-20 is mostly adequate and works fine on every day, light duty vehicles that aren't pushed hard for long periods of time. In an engine where there's lots of continuous high RPM and high loads/heat, a thicker oil is going to give more engine wear protection headroom (higher HTHS, higher MOFT between parts).

IMO, xW-20 is on the borderline of being a bit thin (HTHS of ~2.6 cP) to give much room for heavy engine use (turboed, heavy towing, continuous high speed driving, track use, fuel dilution in GDI engines, etc). Driving around in a normal benign manner where RPM is low or only short durations of high RPM, and keeping oil temps below 225F, then xW-20 will be work fine. Some people still bump up to a 5W-30 just to give that added wear protection headroom buffer, regardless of their driving habits/conditions.


Exactly, if that were the case and the thinner oils really offered better protection across the board cars like the Vette would be running a 20 grade oil. Like everything in life there are trade offs. I doubt that chart takes everything into consideration.

 

[ChrisD46]

Originally Posted by Gokhan
Originally Posted by ZeeOSix
Guess we are reading the plot differently. What I see is increased ring wear at all RPM (except 2000) where the HTHS starts falling below 2.6 cP.

Their curve fits are sloppy to say the least. These are the actual data points. HTHS viscosity = 2.6 cP produced the least ring wear at all rpms except 5000 rpm.

Code
2.2 cP 2.4 cP 2.6 cP 3.1 cP



2000 rpm 0.3 µg 1.2 µg 0.0 µg 0.9 µg

3000 rpm 8.4 µg 7.1 µg 0.6 µg 3.6 µg

4000 rpm 9.3 µg 8.6 µg 5.3 µg 6.3 µg

5000 rpm 7.0 µg 6.5 µg 4.2 µg 3.5 µg

6000 rpm 14.5 µg 13.8 µg 5.5 µg 7.4 µg

*So , using real life conditions in my 2.4L GDI Sonata - in typical suburban driving with some interstate use , I am rarely hitting 4,000 RPM's and above - mostly keeping in the 2,000 ~ 3,000 RPM range for daily driving conditions . This combined with shorter OCI's around the severe schedule mark (3,750 ~ 4,000 miles) would possibly make me a safe candidate for a 5W20 synthetic at 2.7 HTHS (i.e. Valvoline Advanced) ?

 

[ZeeOSix]

Originally Posted by ChrisD46
*So , using real life conditions in my 2.4L GDI Sonata - in typical suburban driving with some interstate use , I am rarely hitting 4,000 RPM's and above - mostly keeping in the 2,000 ~ 3,000 RPM range for daily driving conditions . This combined with shorter OCI's around the severe schedule mark (3,750 ~ 4,000 miles) would possibly make me a safe candidate for a 5W20 synthetic at 2.7 HTHS (i.e. Valvoline Advanced) ?


I'd say yes, those are not very demanding conditions so you would be fine with 5W-20 as long as you GDI doesn't have much fuel dilution.

 

[ChrisD46]

Originally Posted by ZeeOSix
Originally Posted by ChrisD46
*So , using real life conditions in my 2.4L GDI Sonata - in typical suburban driving with some interstate use , I am rarely hitting 4,000 RPM's and above - mostly keeping in the 2,000 ~ 3,000 RPM range for daily driving conditions . This combined with shorter OCI's around the severe schedule mark (3,750 ~ 4,000 miles) would possibly make me a safe candidate for a 5W20 synthetic at 2.7 HTHS (i.e. Valvoline Advanced) ?


I'd say yes, those are not very demanding conditions so you would be fine with 5W-20 as long as you GDI doesn't have much fuel dilution.

*The amount of fuel dilution in the 2.4L GDI is unknown , so keeping the OCI low (<4,000 miles) ) should hopefully help in that regard to keep the HTHS from falling below that 2.6 ~ 2.7 range .

 

[BlueOvalFitter]

WOW! 9 pages of 5W20 VS 5W30. I think this is BITOG's longest debate on these 2 oil weights.
If I had a choice of the 2 it would be a name brand 5W30.

 

[kschachn]

And yet wayyyy back on page 2 (the same day the first post was made) he said:

Originally Posted by csandste
I intend on making my weight decision and announcing it by the time this thread hits the bottom of the display stack.

 

[ChrisD46]

Originally Posted by ZeeOSix
Forgot to mention that xW-20 is mostly adequate and works fine on every day, light duty vehicles that aren't pushed hard for long periods of time. In an engine where there's lots of continuous high RPM and high loads/heat, a thicker oil is going to give more engine wear protection headroom (higher HTHS, higher MOFT between parts).

IMO, xW-20 is on the borderline of being a bit thin (HTHS of ~2.6 cP) to give much room for heavy engine use (turboed, heavy towing, continuous high speed driving, track use, fuel dilution in GDI engines, etc). Driving around in a normal benign manner where RPM is low or only short durations of high RPM, and keeping oil temps below 225F, then xW-20 will be work fine. Some people still bump up to a 5W-30 just to give that added wear protection headroom buffer, regardless of their driving habits/conditions.

*I see mostly 5W20 oils are HTHS 2.7cP , so you get a slight bump above the 2.6 cP mark .

 

[Gokhan]

Originally Posted by mcwilly
Thanks for the reply Gokhan

You're welcome!

I would also like to add that if you are looking at two oils with identical HTHS viscosities, the one with a higher VII content and/or a higher viscosity index VI will result in better fuel economy but also more engine wear, everything else given equal.

The reason is twofold.

The first one is simple. The HTHS viscosity is measured at 150 °C but the oil temperature is usually significantly below that, perhaps between 100 - 120 °C. Therefore, the oil with a higher viscosity index VI will run thinner at most operating conditions, resulting in better fuel economy but also higher wear.

The second one is more subtle. The HTHS viscosity is measured at a shear rate of 1,000,000 1/second. The oil with a higher VII content will have a thinner base oil, which will increase the wear in certain engine parts (especially the valvetrain and timing chain) but it will also improve the fuel economy because when the shear rates in the bearings increase beyond 1,000,000 1/second, such as in high-rpm and/or high-load conditions, the oil with a higher VII content and a thinner base oil will have a "higher-shear" viscosity that is lower at these increased shear rates. This reduced friction in the bearings and the accompanying increase in the fuel economy comes at the cost of potentially higher bearing wear.

So, in summary choose oils with the lowest viscosity indexes (VI) and lowest VII content for the least engine wear and choose oils with the highest viscosity indexes (VI) and highest VII content for the best fuel economy. The two are of course contradictory -- one comes at the cost of the other.