OK I dont get it....!

[Strjock81]

From everything I have read, the only difference between a 5w30 and a 10w30 oil (or say 5w-40 and 15w40) is that the lower the Xw number, the easier it starts and the oil flows better when cold. Also, it will tend to shear down faster than the higher Xw oil. However, at operating temps, the only thing that matters is the higher number, I.E., the 20, 30 40, etc. So why are some OEMs so particular about using a 10w30 over a 5w30 when it is warm out? Warm engine/weather protection should be the same, and as long as manufacturer recommended OCIs are observed, the 5w30 should not shear down enough to make a big difference in 100c viscosity, right? I guess to my way of thinking, why would you ever use a 10w30 when you could use a 5w30, providing you used an OCI that assured that the 5w30 wouldnt shear out of grade?

Furthermore, being a diesel guy, does a 5w-40 syn like delvac 1 shear down faster or slower than a 15w40 mineral oil like Delo? And why do some oil companies call an oil a 15w40 when in fact it meets the specs for say 5w-40--does not the Amsoil 15w40 syn flow like a 5w? I see all the time how syn oils boast their better cold flow rates than similarly labeled conventional oils, yet still label them as the same weight oil. Should they not be a lower Xw in that case? Is this so there is no confusion among uneducated consumers who might think they are doing harm by not running the Xw-X weight oil that is recommended by their engine manuf.?

 

[Gene K]

All else being equal (it seldom is) a 5W will tend to shear more than a 10W or 15W.

It is a lot more important to look at how the oil is constructed than just its cold start numbers.

For instance a 0w30 like German Castrol Syntec with better Basestock is alot more likely to hold up than a 10w30 SL/GF+3 like Mobil Driveclean. The GC is also a higher viscosity oil than the DC (212&#176F) and so is a better choice for high temp conditions.

In the case of HDEO... The primary difference between the Synthetic 5W-40 vs Conventional 15w40 seems to be that the Synthetic has better Cold Start Properties and it holds up better (TBN) over extended drains. The primary difference in spread is from the natural difference in VI in the different base stock not a increase in VII.

Gene

 

[OffOrWFO]

It sounds like you actually have pretty good understanding. I think a lot of the 5w vs 10w recommendations are because of poor oils of the past. Is this a something you have seen on a new vehicle? In the past some oils with wide viscosity ranges have caused problems because of low quality VII used. It's the same reason GM had a ban on 10w-40 years ago. Oils with less spread just had a better ability to maintain it's viscosity. Now days most oils are good enough that shearing seldom happens. There are those that still like 10w30 over a 5w30 here. IMO if your running a normal OCI any 5w30 will hold up just fine. If your going for long OCI and live in a warm climate then a 10w may be the way to go.

On the diesel oil, I think any oil will last a long time. All of the analysis that I have seen on HDEO that are considered "no longer good for service" are because of high wear numbers, high soot or fuel dilution. You seldom see one that needs to be changed because of shearing down.

The amsoil 15w40 has a vis of 100.2cst @40c and a -44c/-47F pour point. Their 10w-40 is 90.5@40c w/ a -48c PP. The 5w-40 is 83.6cst @40c w/a -51c PP. So their 15w isn't really a 5w although it will still pump at low temps were as some conventional 15w40 oils have a PP as high as -15F. The amsoil is designed for guys who want to never change their oil again so it is made with maximum longevity in mind. The 5w-40 delvac probably wouldn't last as long but you have to run very long OCIs to find the point were it starts to shear. On the other hand Mobil 1 0w-40 is knonw to shear under hard use but most who use it are ok with it as they wanted a thin 40wt or thick 30wt anyway. I hope may ramblings have answered some of your questions.

 

[Dr. T]

You answer your own question and then you ask it again.

All else being equal, a straight 30 weight will be the most shear resistant. As soon as you start adding pour point depressants to "make" an oil a 10W or 5W, it is 'weakened' and will tend to shear down with use. Therefore, yes technically a 10W will have more cojones than a 5W....so would a 15W30 if there was one.

As far as the Delvac comment...yes, they have a 'commerical grade' oil that happens to have all the commercial standards met and can be a 5W probably because it's a synthetic. Just like Shell's Rotella (commmercial grade) is a 0-40. Traditional commercial grade oils were a conventional 15w40. You can't make a conventional 5w40, and the most shear stable dino is a 15-40.

As far as your Amsoil comment. If it is a 15-40, it's probably a 15-40. In other words, where do you get your 'flow rate' info from? A 15W pumps down to -20C to -25C irrespective of pour point. I would stick by the label...it may pour to a much lower point, but if it's labelled a 15W, it will probably only 'pump' down to the SAE denoted levels.

 

[Strjock81]

quote:

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The amsoil 15w40 has a vis of 100.2cst @40c and a -44c/-47F pour point. Their 10w-40 is 90.5@40c w/ a -48c PP. The 5w-40 is 83.6cst @40c w/a -51c PP. So their 15w isn't really a 5w although it will still pump at low temps were as some conventional 15w40 oils have a PP as high as -15F.

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Yes but you are comparing amsoil oils to amsoil oils, all of which pump, or supposedly pump better than their similarly labeled conventional counterparts. How, just for example, does it pump relative to Pennzoil 10w40 conventional, or Delo?

Pennzoil 10w-40 visc. is 88 at 40c, 13.5 at 100c

Delo 400 15w40 is 125 at 40c, 15.1 at 100c

Pour point is -31, cold crank viscosity is -20.


CCS Viscosity @ -20°C Amsoil= 3600
CCS Viscosity @ -20°C Delo = 6500
CCS Viscosity @ -25°C Pennzoil =
??? Hard to make any conclusions I suppose. Looks to me like Amsoil 15w40 is a lot closer to a 10w than a conventional 15w.

 

[Strjock81]

Now I see Amsoil straight 30wt diesel oil has a visc of 85.4 at 40c. Lower then Pennzoil 10w-40's number! Shouldn't it have a relatively poor 40c number?

 

[TallPaul]

quote:

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Originally posted by Dr. T:
...so would a 15W30 if there was one.

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Try 3 quarts 10w30 mixed with 2 quarts straight 30. Should be about a 15w30 or so.


I would guess that 5w20, 10w30, 15w40, and 20w50 are roughly similar in how much they proportionately are spread out by viscosity index improvers (VIIs) and so each should be equally robust as to not sheering. The wide dinos are 5w30 and 10w40, which I suspect are similar in their proportionate VII spreads, with perhaps 10w40 being the more robust of the two.

 

[1 FMF]

quote:

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Originally posted by Strjock81:
Now I see Amsoil straight 30wt diesel oil has a visc of 85.4 at 40c. Lower then Pennzoil 10w-40's number! Shouldn't it have a relatively poor 40c number?

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from the viscosity label, for example 10w30, the number before the W, 10, which is referred to as winter weight or winter viscosity, has nothing to do with the viscosity measured at 40C temperature. I remember asking that I while ago. 40 Celsius is 104 Fahrenheit, certainly not cold. The oil's winter viscosity refers to how well it flows when cold, see http://www.infineum.com/information/viscosity.html for the SAEJ300 chart.

A 15W-x oil has a max cranking viscosity of 7000 cP at -20C. A 10W-x oil a max crank viscosity of 7000 cP but at -25C. A 5W-x is 6600 cP at -30C.

For conventional oils, the higher the spread between winter viscosity and operating viscosity (at 100C) may suggest that it will be more shearable, such as a 5w30 versus a 10w30. This is because of the viscosity index improvers used to blend the oil to those characteristics to meet those specs, they are what shear and cause the oil to lose viscosity or break down. But this doesn't hold true for all oils. The shear resistance has more to do with the quality of the base oil, and also with the amount and quality of VII and additives used. For quality (synthetic) basestocks, they are inherently better at cold temps and meet those cold crank viscosity specs without a great need for VII, one of the reasons why they are better and more shear resistant. This explains the reason a synthetic monograde oil can flow like a 10w30 oil, or meet that W rating. And generally, a synthetic will have lower viscosity at colder temps, from 40C (100F) and lower. It is sometimes a way, I think anyway, of being able to spot a good synthetic oil, or an imposter, by comparing these ratings versus it's pricetag.

The reason carmakers spec 5w30 over 10w30 is for fuel economy and EPA pressure. The 5w30 has, generally, less viscosity at all temps below the operating temp of 100C (212F). Less viscosity = less friction or resistance = less power lost = more fuel economy. Even when it's warm out, say 100F in the southwest, it is still cold from the motor's perspective. So recommending or requiring the 5w30 for that < 1% difference in fuel economy for the 10 minutes of run time is apparently justified over millions of vehicles.

Delvac 1 5W-40 I have reported at 3200 @ -20C. The 5W spec is < 6600 @ -30C. I guess we need to know what the 5W spec is at -20C. Mobil delvac1300 15w40 is 6000 @ -20C.
Amsoil diesel/marine 15w40 is 3600 @ -20C. What it is at -25C for the 10W spec who knows, I guess it isn't less than 7000 cP.
Many report the delvac1 being one of the most shear stable of any oils, and claim it to be because of it's high quality base oil. It is a synthetic oil, which then explains how it can meet the 5W rating, and why it costs so much more.

I also need to point out that many different ASTM #'s are reported for these cold crank or cold pump tests. The SAE J300 chart refers to ASTM D5293 for cold crank, and D4684 for cold pump. But the numbers I have from Amsoil refer to ASTM D2602. Maybe this is one source of the confusion?
I also have a word doc of all the major brands properties, viscosity, pour/flash points, VI, etc. PM or email me your email if interested and I will send it to you.

[ December 22, 2004, 03:02 PM: Message edited by: 1 FMF ]