Why are most 20 weight oils borderline 30 weights?

[stranger706]

Reading through StevieC's Redline post made me wonder why most of the 20 weight oils are borderline 30 weights. Why don't the oil companies make a "middle" 20 weight or a "thin" 20 weight?

Are they afraid of excess wear?

For example, RL's 5w20 is basically a 5w30, which they already produce. So whats the point of making the 5w20 so thick?

To me, their 0w20 is more of a "real" 20 weight than their 5w20. Can anyone see this or am I out in left field?

 

[MarkC]

Maybe some 5W30's are really borderline 20's instead of the other way around?

 

[erogers]

Take a look at Wolf's Head 5W-20 (both conventional and synthetic):

Super-Duty
Visc cSt @ 40C: 37.0
Visc cSt @ 100C: 6.30

Syn-Pack
Visc cSt @ 40C: 38.0
Visc cSt @ 100C: 6.80

You're right about many 20 weights being borderline 30 weights, but here are at least two "thin" 5W-20 oils.

 

[StevieC]

Maybe because they want it to shear to a solid 20wt over the course of the OCI?

Maybe because getting any thinner than an actual 20wt is asking for trouble?

Just speculation...

 

[Gary Allan]

It's probably just easier to make spec.

 

[Merkava_4]

Originally Posted By: MarkC
Maybe some 5W30's are really borderline 20's instead of the other way around?


The Havoline is!

 

[CATERHAM]

Originally Posted By: stranger706
Reading through StevieC's Redline post made me wonder why most of the 20 weight oils are borderline 30 weights. Why don't the oil companies make a "middle" 20 weight or a "thin" 20 weight?

Are they afraid of excess wear?

For example, RL's 5w20 is basically a 5w30, which they already produce. So whats the point of making the 5w20 so thick?

To me, their 0w20 is more of a "real" 20 weight than their 5w20. Can anyone see this or am I out in left field?


I've wondered this myself.
There aren't too many 20wt oils that are over 9.0 cSt @ 100C, most are in the 8.0 to 8.8 range.
I think part of the answer may be that the SAE 20wt range is too broad (5.6 to 9.29 cSt @ 100C). Percentage wise the range is much larger than the heavier grades.
For exanple there's a big difference between a 6.5 and 8.5 oil but RP calls it's 0W-10 oil which a 100C vis of 6.5 a 10wt although it clearly fall in the 20wt vis range. I think the reason is to differentiate it from it's other heavier 20 weight oils.
Another reason may be the 20wt requirement that the HTHS vis must be at least 2.6 cP. I suspect most 20wt oils, particularly dino's can't maintain a 2.6 vis with a 100C vis below 8.0 cSt.

 

[G-MAN]

Originally Posted By: CATERHAM
Another reason may be the 20wt requirement that the HTHS vis must be at least 2.6 cP. I suspect most 20wt oils, particularly dino's can't maintain a 2.6 vis with a 100C vis below 8.0 cSt.


Bingo.

 

[stranger706]

Originally Posted By: G-MAN
Originally Posted By: CATERHAM
Another reason may be the 20wt requirement that the HTHS vis must be at least 2.6 cP. I suspect most 20wt oils, particularly dino's can't maintain a 2.6 vis with a 100C vis below 8.0 cSt.


Bingo.

That makes sense. I hadn't thought about that.

So basically the oil mfr. sets out to make a 20 weight, with a minimum HTHS of 2.6, and the result is a 100C of 8+ cst.

I wonder how long before the minimum of 2.6 is lowered, and we start to see 0/5w10 weight oil being spec'd.

 

[G-MAN]

Originally Posted By: CATERHAM
I think part of the answer may be that the SAE 20wt range is too broad (5.6 to 9.29 cSt @ 100C). Percentage wise the range is much larger than the heavier grades.


SAE J300 specs such a broad range for 20 weight oil because SAE 20 is the only straight grade that has both a high and low temp (cold cranking/cold pumping) spec. Before the advent of Group II base oils, an oil blended to meet SAE 20W specs would not have a sufficiently high HTHS to also be labeled as SAE 20. And vice versa. An oil blended to meet the HTHS requirement for SAE 20 would not pass the CCV and low temp pumping requirements for SAE 20W. A few oil companies using really good (usually Penn Grade) base oils could blend 20w20 back in the 50s and 60s. With modern Group II base oils, a 20w20 is no problem.

But in modern 5w20 oils, that pesky 2.6 HTHS requirement is still there, and with Group II base oils you pretty much have to have a finished 100C vis of around >8.0 to meet it. With Group III or PAO you could probably meet it with >7.0.

 

[JohnBrowning]

Well I am thinking that the fact that 5W30 dino often sheared to a 5W20 in under 3000 miles gave them the idea to try 5W20. Since they new that 5W30 when shered to a 5W20 did just fine in the protection department it made sense to start their and engineer an oil that started at that sheared point and design it not to shear to be more shear stable then dino 5W30.

Often men even smarter then me also find that reinventing the wheel is pointless unless needed. Start with a known starting point and if it does not work out then you can wiggle either directions you follow. Since it worked probably the first try I would imagine they probably wrote the spec. around what they had already proven to work. This happens more often then people think!

 

[mechtech2]

Great answer, G-MAN! Done.

 

[Herz]

Originally Posted By: Merkava_4
Originally Posted By: MarkC
Maybe some 5W30's are really borderline 20's instead of the other way around?


The Havoline is!


and its brother, chevron supreme.