A 5W is not a 5W is not a 5W

[Jax_RX8]

When we measure the viscosity of oils at 100C (xW20, xW30, xW40 , etc) they all are generally within the published ranges for 20 , 30 , 40 weight oils.

Why then, does a 5W viscosity (at 40C per ASTM D-445) vary so wildly, depending on the operating viscosity.

For instance, I looked up some RLI oils and found the following (just used them because it was easy to look up, but everyone else does the same thing) viscosity's for each of the following at 40C (the first number):

5W20 - 45 cSt
5W30 - 59 cSt
5W40 - 90 cSt

Ironically, I also looked up their 10W30, and it is rated at 73 cSt - thinner at 40C than the 5W40!

Again, these numbers are typical for all brands and not unique to RLI.

I know how this is happening via the formularies, but the real question is why is a 5W40 allowed to be called a 5W when it's viscosity is higher at 40C than a 10W30?

And why does a 5W20 have a viscosity that is half as much as a 5W40 at 40C, but both are called 5W? This is VERY misleading to oil customers as they do think they are the same viscosity at room temp (or colder) and they are not!

Thoughts?

 

[pbm]

Good question. I've always wondered the same thing.

 

[ericthepig]

The 5W does not describe the properties at 40C. That's pretty much ambient temps. The 5W describes the flow properties at very low temps (neg. degree C) - but I can't remember the exact temp.

 

[addyguy]

I don't know the details, but the '5W' number is the cold flow/pump number...measured by cst at -30C...the 40 deg. C number is a much warmer temp number, and the oil will be thicker/thinner depending on 'where it is going' - 5W to 30; 5W to 20, or 5W to 40...etc....

A 5W-40 is overall a MUCH thicker oil that a 5W-20, it just happens to also be able to meet the cst @-30 cranking number that a 5W oil needs, but it is still a thicker oil...

 

[Drivebelt]

The 5W specifications aren’t measured at 40C. They're measured -30C (CCS - cold cranking) and -35 (MRV - pumpability).

Since a 5W only has to be below a certain specification (6600 cP @ -30C for CCS). It could be well below that specification, say 4000, or it could be 6500.

Different 5W oils also have different VI's (viscosity indexes), which means as the temperature changes, 2 different 5W's won't go through the same viscosity change. 2 different 5W oils could start out at the same 5000 cP (at -30C), but as the temperature changes, they won't go through the same viscosity change because of the different VI's.

 

[Jax_RX8]

OK, so I found it, the xW number is based on the ASTM-D-5293 CCS spec/test.

To qualify as a 5W, the cSt must be under 7000 (this is right) at -30C
To qualify as a 10W, the cSt must be under 7000 at -25C
etc, etc.

I guarantee you that 99% of oil customers think that all 5W oils are the same viscosity cold (whatever their definition is of cold).

The way this spec works and it being utilized to determine the first number of an oil weight is very misleading to the average user. Heck, I just looked up M1 0W40 and at 40C, it is also about the same viscosity as a 10W30 - very misleading way of labeling IMHO.

 

[RI_RS4]

Well, that would be due to the fact that the viscosity at 40C has nothing to do with a W oil rating. The basic criteria are, Cold Cranking and Pumpability

The requirement for a 5W oil in 1989 was:

3500 cSt @ -25C SAE J300 (Cold Cranking Simulator)
30000 cSt @ -25C ASTM D4684 (Pumpability)
3.8 cST @ 100C ASTM D445 (Min high temperature viscosity)


low-temperature viscosity from "Low Temperature Lubricant Rheology Measurement and Relevance to Engine Operation"

It appears that the SAE specifications were changed sometime in the 90's to what others are now posting:

2004 Engine Oil Viscosity Tables

 

[Quattro Pete]

The spec isn't ideal, but I wouldn't call it misleading necessarily, at least not in the way you portray it. No oil maker out there goes around claiming that first number (before the W) relates to viscosity at room temp or at 40C. Heck, 40C = 104F. That's not even close to a typical room temperature. I think most people associate that first number with cold starts at very low temps - think winter up north.

Obviously, there is a huge group of people that just plainly freak out about that "5w" figure thinking it'll be too thin for their engines when in fact the oil is the thinnest at operating temps and at that point it doesn't matter if it's 0w-30, 5w-30, 10w-30, etc, in general terms.

 

[FrankN4]

What Drivebelt said is exactly on the money, especially about the diferences due to viscosity index.

Old geezers like me remember the word "weight" and have trouble thinking the now correct "grade." A 5W-30 could meet the specks of a 5W-20(100C cSt of 9.3) or the specks of a 5W-40(100C cSt of 12.5) I believe a 10W GM 6094M is very near the minimum of a standard 5W.

Now that I have learned all of the answers, they have changed all of the questions :^(

 

[Gary Allan]

Quote:
I think most people associate that first number with cold starts at very low temps


Well, I think "most people" actually think the oil thins when cold and thickens when hot ..all the while looking at and handling a room temperature bottle of oil. Even some people who know will say "it will be thicker when warm" when referring to a 10w-40 ..while failing to follow it with "..than a 10w-30"...giving the novice the impression that the oil indeed got thicker as it heated.

 

[Titan]

It's just exactly as I thought...

 

[phib]

Originally Posted By: Gary Allan
Quote:
I think most people associate that first number with cold starts at very low temps


Well, I think "most people" actually think the oil thins when cold and thickens when hot ..all the while looking at and handling a room temperature bottle of oil. Even some people who know will say "it will be thicker when warm" when referring to a 10w-40 ..while failing to follow it with "..than a 10w-30"...giving the novice the impression that the oil indeed got thicker as it heated.


Sorry for being a Noob in here, I just need a quick answer with my problem. I was given the thought of, For colder weather ranging from 55-75F a 5w30 would be better for a car with 360whp 4Cyl turbo, Daily driven (sort of) and goes to a drag strip once every 2 months.

However here in Southern California, temp is ranging now from 65-90F and this summer could even go to 70-95F.

I have Motul 300V 5w30 in my car now, and all i can say that it's great.

I'm purchasing oil tomorrow or this comming friday and I have access to get again motul 300V 5w30, Motul 300V 5w40 OR Motul300V 10w40.

Is it true that getting 5w40 for my car is better for this upcomming weather here in SoCAl? OR would I stick to 5w30?

If I get 5w40, wouldnt that be contradicting because isnt it the thicker the oil on hot temps, The more friction you get thus, getting higher temps?

OR its all in Oil to stabilize the temps while the oil thickens?

After explaining to me all this questions, I want to summarize it. Which Oil to get with thr FF conditions as stated.

a. Motul 300V 5w30
b. Motul 300V 5w40
c. Motul 300V 10W40
d. Redline OIL? Which grade?
e. Consider another Oil? >>please state which one.

 

[Shannow]

I still like my rating system, or any other rating system than the one that we've got.

 

[Titan]

For colder weather ranging from 55-75F a 5w30 would be better for a car with 360whp 4Cyl turbo, Daily driven (sort of) and goes to a drag strip once every 2 months.

However here in Southern California, temp is ranging now from 65-90F and this summer could even go to 70-95F.[/B]

First, if you have a well-functioning cooling system, the difference of a few degrees ambient temp may make ZERO difference in what viscosity you should choose for your application.

Secondly, you state Motul is doing "great" in your application. My questions to you are: How do you know? Great compared to what others you've tried, and, again, how do you know?

My suggestion is to determine what oil sump temperatures are seen in your application, and the corresponding viscosities will be a bit easier from which to start the selection process. In your application, all other things equal, a higher HTHS number may be indicated, at least for the drag-strip days.

There's a lot to learn on this site. One thing you'll learn quickly is that there is no such thing as answering your question correctly when the question is "what is the best oil"...it's just not that simple.

 

[phib]

Originally Posted By: Titan

For colder weather ranging from 55-75F a 5w30 would be better for a car with 360whp 4Cyl turbo, Daily driven (sort of) and goes to a drag strip once every 2 months.

However here in Southern California, temp is ranging now from 65-90F and this summer could even go to 70-95F.[/B]


Secondly, you state Motul is doing "great" in your application. My questions to you are: How do you know? Great compared to what others you've tried, and, again, how do you know?


I've Used Mobil 1 5w30 syn before, During hot weather before, my oil temp was high compared to Motul. Plus motul revs my engine better, based on data i got from my logger.

Quote:
My suggestion is to determine what oil sump temperatures are seen in your application, and the corresponding viscosities will be a bit easier from which to start the selection process. In your application, all other things equal, a higher HTHS number may be indicated, at least for the drag-strip days.


Here is a Picture posted by Scuderia about motul 300V 5/30 with UOA. I have no idea how would you determine HTHS there.

Quote:
There's a lot to learn on this site. One thing you'll learn quickly is that there is no such thing as answering your question correctly when the question is "what is the best oil"...it's just not that simple.


That's what I thought, but anyhow, I've been told of by alot of people that I should go 5/40 reason being that I live here in SoCAL and my car is turboed.

I'm just choosing which one to get.

 

[Johnny]

You will be fine with 5W-30 in California.

 

[3putter]

Or anywhere else for that matter.

 

[dailydriver]

Originally Posted By: Johnny
You will be fine with 5W-30 in California.


ESPECIALLY with the 300V (just look at those specs/add pack, etc.

), and for drag race/street only use (EVEN 'hot-lapping'!).

Now IF you were open tracking (road race) or 'time attacking' that thing for extended periods you might think about mixing in a couple of liters of 10W-40 300V with mostly 5W-30.

 

[bob_ninja]

Originally Posted By: Quattro Pete
The spec isn't ideal, but I wouldn't call it misleading necessarily, at least not in the way you portray it. No oil maker out there goes around claiming that first number (before the W) relates to viscosity at room temp or at 40C. Heck, 40C = 104F. That's not even close to a typical room temperature. I think most people associate that first number with cold starts at very low temps - think winter up north.

Obviously, there is a huge group of people that just plainly freak out about that "5w" figure thinking it'll be too thin for their engines when in fact the oil is the thinnest at operating temps and at that point it doesn't matter if it's 0w-30, 5w-30, 10w-30, etc, in general terms.


I am in Canada, so very interested in the 1st number. I used to seek 0Wxx oils for winter. However, I too found the 1st number to be confusing.

Your explanation is very good. I think what happened is that most people percieve these numbers as follows:

xxWyy
xx = viscosity on startup
yy = viscosity after warmup

As you point out the actual definition is based on extreme cold temps -30C/-35C which most people never see. Even here in Canada we don't see -30C often (at least not where I live).

Startup viscosity is not that imoprtant during summer. So we really care about startup viscosity during winter. Given that most winter temps are around freezing, more or less, it would be better to define the 1st number in terms of CCS/MRV at freezing.

So really the definition of xxW is not what most people are interested in, looking for.

Example:
Esso XD3 0W30 40C=71 cSt, 100C=12.1 cSt, VI=168
CCS@-35C=5,900 cP, MRV @-40C=22,600 cP, @-35C=11,200 cP
PP 5W30 40C=59.7 cSt, 100C=10.5 cSt, VI=167
CCS@-30C=4,410 cP, MRV@-35C=6,600 cP
Formula Shell 5W30 40C=64 cSt, 100C=10.7 cSt, VI=157
CCS@-30C=5,446 cP, Borderline Pumping Temp -42C

I orginally got XD3 for winter driving. We tend to range between -20C and freezing. XD3's CCD is very good at -35C which I never see. However, by the time you get to 40C it is already thicker than even a conventional cheap Shell oil.

Of course, from this limited data I cannot tell what is going on around -20C to 0C which is what I really care about. Still, I can guess that XD3 is only thinner at extreme cold.

So even though 0W30 seems to be a better winter oil, clearly PP 5W30 is thinner!?!?! Hence the confusion.

I don't mind CCS/MRV at -35C, just wish more data around 0C.
As pointed out before, the main numbers are useless and these days I have to look at specs.

 

[Jax_RX8]

^^^^^^^^ Very well put and exactly the point I was trying to make.