Is 30 Weight Oil Superior to 20 Weight?? (long)

[OldCowboy]

It seems to be a popular opinion that 30 weight oils are superior to 20 weight oils and the recommendation of 20 weight oils by many manufacturers is due to CAFE requirements.

I decided to compare the UOAs of 25 of the most recent 20 weight oils to 25 of the most recent 30 weight oils. No attempt was made to cherry pick UOA results. Of course this is a retrospective study, not a controlled study.

In order to compare the results of one analysis to another, I normalized the results to ppm/1K miles. As an example, say a UOA had an iron level of 16 after 4685 miles. To convert this to ppm/1K miles, divide 16 by 4.685 (16/4.685 = 3.42).

Here are the results. First the 30 weight oils:

Now the 20 weight oils:

The 20 weight oils not only showed lower average wear levels as ppm/1K miles
but they also showed lower standard deviations, indicating that the 20 weight oils gave more consistent results.

 

[HTSS_TR]

Thanks. It seems to take a lot of times to do these studying/comparing.

 

[toyotapriusguy]

Were the 19 and 20 Fe readings considered acceptable or were they from a really long OCI or from something other than a healthy engine run on an acceptable OCI? Those 2 are very high compared to the other 23

 

[river_rat]

Interesting post. Thanks for the work!

 

[river_rat]

Originally Posted By: toyotapriusguy
Were the 19 and 20 Fe readings considered acceptable or were they from a really long OCI or from something other than a healthy engine run on an acceptable OCI? Those 2 are very high compared to the other 23

These are all "per 1000 miles."

 

[OldCowboy]

The iron reading of 19.02 ppm/1K miles was from a 4.0L Jeep with about 100,000 kilometers (62,000 mi) and had 9500 km (5890 mi) OCI.

The iron reading of 20.63 ppm/1K miles was from a 1200 mile break-in. I should not have included this one. I'm going to remove it and add one from a vehicle that is broken in.

 

[crinkles]

Very interesting, there are of course many limitations to the data sets (incl. different vehicles, non linear generation of ppm wear metals, etc etc)

BUT, very interesting nontheless, thanks for the effort.

 

[hhu168]

Originally Posted By: OldCowboy
The iron reading of 19.02 ppm/1K miles was from a 4.0L Jeep with about 100,000 kilometers (62,000 mi) and had 9500 km (5890 mi) OCI.

The iron reading of 20.63 ppm/1K miles was from a 1200 mile break-in. I should not have included this one. I'm going to remove it and add one from a vehicle that is broken in.


Even if you remove these two and replace them with two closer to the average, it would only lower the average by a little over 1.

Instead of 4.99 vs 2.33, you will have something like 3.70 vs 2.33.

 

[Panzerman]

YES, 30 weight is superior.

 

[demarpaint]

Nice job, thanks for the effort. Hopefully this doesn't end in a thick vs. thin war and a locked thread.

 

[uart]

It would also be interesting to include the average "miles on unit", to see if there's any statistical difference there, if you re-do the calculations OldCowboy.

Even more interesting would be to see the same calculations repeated with a different starting point (going back further) to see if the results are in any way repeatable.

 

[OldCowboy]

Actually, going forward, I'm going to add new UOAs to the spreadsheet as they are posted in the UOA forum. 25 samples from each class is a start, but 100 samples per class will be more meaningful.

Also, I have and will continue to exclude samples which have additives like MMO in them.

 

[Oregoonian]

The 20 weight oils not only showed lower average wear levels as ppm/1K miles
but they also showed lower standard deviations, indicating that the 20 weight oils gave more consistent results.[/quote]

Originally Posted By: Panzerman
YES, 30 weight is superior.

Panxerman.....are you reading the same conclusion...as I am???

20 weight rules!

Nice work OldCowboy.....appreciate all the time and effort.
___________________________________________
03' Ford Focus (2.3L Duratec PZEV) / 98K
PP 5w20 / Purolator PureOne / OCI: 7,500 +/-

 

[fdcg27]

I don't think that anyone doubts that thicker oils produce lower wear numbers in similar conditions.
We should all also know that UOAs are all about the life of the oil in a given application, not engine wear.
We all also know that engines are made to wear, and that any given vehicle in any given use is likely to be driven to its grave on its original engine without regard to the grade of oil used.
The car as a whole wears and ages out.
A car is far more likely to be junked due to a failure of its automatic tranny than of its engine.
Engine wear is far from a major concern using any grade oil changed on any reasonable basis.
Remember, also, that the wear numbers are in parts per million, so a 2X difference isn't that great in absolute terms.
Nonetheless, a nice effort by the OP.

 

[dparm]

Agreed, most motors will outlast the cars they're put into almost regardless of the oil choice.

 

[Hallmark]

I see no evidence to persuade me to discontinue using Motorcraft 5W-20 motor oils.

Thanks for the effort expended in the portrayal.

 

[chubbs1]

Thanks a lot for posting this very interesting report. (I know it has limitations as well) but this is the first time someone actually put some effort into analyzing the numbers rather than conjecture.

WELL DONE!!

 

[Oregoonian]

Originally Posted By: fdcg27
I don't think that anyone doubts that thicker oils produce lower wear numbers in similar conditions.
We should all also know that UOAs are all about the life of the oil in a given application, not engine wear.
We all also know that engines are made to wear, and that any given vehicle in any given use is likely to be driven to its grave on its original engine without regard to the grade of oil used.
The car as a whole wears and ages out.
A car is far more likely to be junked due to a failure of its automatic tranny than of its engine.
Engine wear is far from a major concern using any grade oil changed on any reasonable basis.
Remember, also, that the wear numbers are in parts per million, so a 2X difference isn't that great in absolute terms.
Nonetheless, a nice effort by the OP.

But this research... seems to say that 20 weight...."showed lower average wear levels".....than 30 weight.

I DOUBT that....thicker oils produce lower wear numbers.
__________________________________________

03' Ford Focus (2.3L Duratec PZEV) / 98K
PP 5w20 / Purolator PureOne / OCI: 7,500 +/-

 

[Gene K]

Originally Posted By: Oregoonian



Originally Posted By: Panzerman
YES, 30 weight is superior.

Panxerman.....are you reading the same conclusion...as I am???



Of course he is! 3000 mile 10W30 Synthetic Oil changes are better than 10000 mile 5W20 Conventional Oil Changes in a Honda Civic because they make us feel better.

 

[ericthepig]

My name is in lights.

Thanks for running these numbers! Still very pleased with PU 5w20 with its comparatively good numbers even on an ~13k mile OCI.