10w30 = 5w30 = 0w30 at operating temperature??? ??

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10w30 = 5w30 = 0w30 at operating temperature, right? Given a single brand, say, Pennzoil Platinum, the viscosity of oil should be the same! right? but reading this forum for a year, I pick up little hints that suggest otherwise, there is this sense that the *TRUE* viscosity goes like this: 10w30 > 5w30 > 0w30 any truth to this?
 
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no. They're all 30 weight, so they have to be between 9.3 and 12.5 cSt at operating temperature, but they can fall anywhere in that range. The 5W-30 could be thicker than the 10W-30 at operating temp. Without pulling up datasheets, you can't make any assumptions.
 
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 Originally Posted By: mareakin
10w30 = 5w30 = 0w30 at operating temperature, right? Given a single brand, say, Pennzoil Platinum, the viscosity of oil should be the same! right? but reading this forum for a year, I pick up little hints that suggest otherwise, there is this sense that the *TRUE* viscosity goes like this: 10w30 > 5w30 > 0w30 any truth to this?
The problem is that there's a lot of variability allowed in what can be called a "30" or a "20." So even within brands, sometimes the 10w30 may be thicker than the 5w30 at operating temp. But ideally, they should all be very nearly the same at operating temp. There's also a lingering feeling among a lot of people that a straight 30 will "always be thicker" than an Xw30 at high temperatures, but that's not always true either. Just for giggles once I pulled down the specs from Royal Purple's website, and their 10w30 is actually thicker than their SAE 30 at 100C. The argument that a straight 30 weight with no VI improvers will be more reliable at high temp than an oil with a whole lot of VI improvers is also true... but in today's world the oil companies are making VII-less (or at least minimal VII and high-quality VII) 0w30, 5w30, and 10w30 oils from high viscosity index base stocks and by using pour-point depressants to get the "O" rather than relying solely on VIIs to get the "30." So now that I've made a whole bunch of conflicting statements, I'll just say "it depends on the particular oils you're comparing" and walk quietly away... Fortunately lots of oils have these specs published online, so you can look for yourself before buying.
 
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Indeed 5W-30 "could be" as thick or thicker than an equivalent branded 10W-30 at operating temp. But I think this advantage is short lived in most cases as 5W-30 tends to sheer. This is why some applications such as GM 3800s alternately recommended 10W-30 and 5W-30 depending on the year and the model. Some model years of the engine were thought to run a bit hotter and 10W-30 was made the preferred oil due to its ability to better resist heat over the OCI... All things being equal; there probably isn't much of a difference in most vehicles from 5W-20 to 10W-30 and little advantage in using 10W-30 anymore...
 
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 Originally Posted By: Nickdfresh
But I think this advantage is short lived in most cases as 5W-30 tends to sheer. This is why some applications such as GM 3800s alternately recommended 10W-30 and 5W-30 depending on the year and the model.
Most cases? I don't know what oil you're using, but as long as it's SM rated, it has to have a pretty decent base stock, and sheering on a 5W-30 isn't much of an issue. I've been dealing with the 3800s for a while now, and I've never heard that explanation. It was around the time of the switch to SL that they started recommending 5W-30.
 
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 Originally Posted By: Scimmia
 Originally Posted By: Nickdfresh
But I think this advantage is short lived in most cases as 5W-30 tends to sheer. This is why some applications such as GM 3800s alternately recommended 10W-30 and 5W-30 depending on the year and the model.
Most cases? I don't know what oil you're using, but as long as it's SM rated, it has to have a pretty decent base stock, and sheering on a 5W-30 isn't much of an issue.
Okay? Are you agreeing with me or quibbling? I can't be sure which. But you are correct, 5W-30 "sheers" in all cases and sometimes goes down to roughly a 5W-20 weight, which I'm pretty sure I've already indicated isn't really "much" of a problem. It isn't "much of an issue." But that doesn't mean that 10W-30 might have some benefit in some applications such as extended highway jaunts in the summer on an older vehicle, or where consumption is an issue...
 Quote:
I've been dealing with the 3800s for a while now, and I've never heard that explanation. It was around the time of the switch to SL that they started recommending 5W-30.
Good. Then maybe you can explain why they initially recommended 5W-30 long before SL (including on my old 1990). Then went to 10W-30 on some models such as the Chevy Malibu even after SL was out? Incidentally, I'm using 5W-30 ML...
 
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188
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So you're saying that an SM 5W-30 is going to sheer down to a 20 weight? Sure, whatever. Yes, GM may have recommended 5W-30 in some older engines that could use a thinner oil (after sheering with the oils available at the time). What does that have to do with anything? And what are you talking about with the Malibu? The Malibu never got the 3800.
 
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When you start and warm your car at a moderate ambient temp, there is little difference. I'm using 10w-30 in my 5w-20 engine and it's just as good in the visc department.
 
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St. Petersburg, FL USA
 Originally Posted By: Scimmia
So you're saying that an SM 5W-30 is going to sheer down to a 20 weight? Sure, whatever. Yes, GM may have recommended 5W-30 in some older engines that could use a thinner oil (after sheering with the oils available at the time). What does that have to do with anything? And WTF are you talking about with the Malibu? The Malibu never got the 3800.
First off, simmer down... Secondly, I have a UOA with SM Mobil 1 that sheered down to a 5W20 in 7k miles... UOA
 
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What's with all this 5w-30 <i>always </i> sheers to a 20wt [censored]? Sure, it happens with cheaper oil but this is a half truth that's gotten out of control.
 
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 Originally Posted By: Scimmia
So you're saying that an SM 5W-30 is going to sheer down to a 20 weight? Sure, whatever.
For the most part, yes. Conventional 5W-30s generally sheer down a bit in most UOAs in the 5000 mile range, especially those involving highway driving...
 Quote:
Yes, GM may have recommended 5W-30 in some older engines that could use a thinner oil (after sheering with the oils available at the time). What does that have to do with anything?
Um, I dunno. You tell me. You're the one saying that 3800s generally went to 5W-30 when the "SL" generation came out, not me. I was just pointing out that that was a bit of an oversimplification. What's your point in even responding to my posts?
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And WTF are you talking about with the Malibu? The Malibu never got the 3800.
Oh sorry. Silly me! I think I meant the Impala. Not that it's really that relevant since we're talking engines, not actual models...
 
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 Originally Posted By: BuickGN
What's with all this 5w-30 always sheers to a 20wt [censored]? Sure, it happens with cheaper oil but this is a half truth that's gotten out of control.
Um, neither I nor the poster you directly responded said "always." He graciously posted a UOA as an example meaning he actually donated a wee bit of cash and time to further the site knowledge base... I said "tended to" sheer. Obviously, some don't. Especially short trippers and those who change at the traditional 3000 mile OCI. But more often than not, 5W-30 oils tend to sheer down a bit to the 5W-20 range. And there really isn't anything wrong with that in most cases... But seeing as you love 5W-30, and thinner oils in general, and use it in everything --I can see why you are offended at this perceived urban myth.
 
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All the same, probably not. All in the same range and thus counted as "30 weights", yes. You could check the actual mfg. data sheets for the oils you are interested to find out whats up with any particular group of oils you want to compare. The funny thing is, one 0W-30 might be thicker at operating temperatures than another 10W-30 is. German Castrol, for example, is a 0W-30 oil which runs on the thick side of the 30 weight spec. For most people, these subtle differences don't really matter.
 
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 Originally Posted By: oilyriser
If operating temperature is 100C then they are the same.
No two oils are the same, even if both are 5W-30. That applies to viscosity also. The guidelines for labeling viscosity are quite loose and the latitude given to manufacturers is wide enough to drive a Mack truck them them.
 
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 Originally Posted By: Nickdfresh
 Originally Posted By: BuickGN
What's with all this 5w-30 always sheers to a 20wt [censored]? Sure, it happens with cheaper oil but this is a half truth that's gotten out of control.
Um, neither I nor the poster you directly responded said "always." He graciously posted a UOA as an example meaning he actually donated a wee bit of cash and time to further the site knowledge base... I said "tended to" sheer. Obviously, some don't. Especially short trippers and those who change at the traditional 3000 mile OCI. But more often than not, 5W-30 oils tend to sheer down a bit to the 5W-20 range. And there really isn't anything wrong with that in most cases... But seeing as you love 5W-30, and thinner oils in general, and use it in everything --I can see why you are offended at this perceived urban myth.
I wasn't referring to anyone in particular it's just that everytime 5w-30 is mentioned someone has to respond with "it shears to a 20w anyway" remark. I sense a bit of sarcasm in that last remark, looking at my sig, it's obvious I'm far from a thin oil guy.
 
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All oils shear. To what degree is the question and whether they stay in grade. If an oil starts out on the high end of the viscosity range for that weight it can shear more and still stay in grade. Shearing resistance depends on base oil, additives and use.
 
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