Would you use Group III 5W-50 oil?

J

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434
Location
Berkeley
Hi, Would you use Group III 5W-50 oil? Group III by its very nature are smaller chain molecules which without viscosity modifiers cannot achieve viscosity higher than SAE 30 (from Bob's excellent presentation on base stock)? So, a Group III 5W-50 oil (such as Castrol "fully synthetic" 5W-50) should have loads of viscosity modifiers which will shear easily over time right? [Cheers!] Jae
 
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450
Location
Louisville, KY
I would try to avoid a group III with such a wide spread. About the maximum spread Id accept, would be 5w-40, which is an extremely common grade in europe. Fred.. [Smile]
 

MolaKule

Staff member
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21,599
Location
Iowegia - USA
I would use a GRIII only if: 1. Price was same as GII+ 2. Tests showed promising wear results. I am not covinced as yet. I would certainly not use ANY 5W50, too much a viscosity spread, too many VII's.
 
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2,480
Absolutely! Why not guys? All OTC synth's are Group III except for M-1 and they don't even make a 5-50. I'd love to know out of those that posted "NO"...how many have tried it? Granted, none of these (including M-1) is as good as Amsoil or Redline or Motul or European Castrol or any other European synthetic, but it they're "acceptable" as far as N.A. "Wal-Mart" obtainable oils are concerned. I would choose it over M-1 15-50 and I challenge anyone whose using M-1 15-50 to do a back-to-back comparison and tell us which they prefer. As far as the VII thing. Let's just say ALL oils have them. How many in the 0-30? The 0-40? 10-60? And the protection afforded by a 50 weight IMHO superceeds the worry about VII's that are probably problematic with thinner 30 weight oils instead since these cook better in your engine. And much easier on the engine and fuel economy during -20 C starts.
 
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23,591
I get the impression that Dr. T and I are the only people here who are not suspicious of 5W-50. Now, I can speak only for my experiences with Syntec 5W-50, and they've been good for 80k miles. PS: Mobil sells M1 5W-50 in Europe (maybe in OZ, too?)
 
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509
Location
Las Vegas, NV
I am also using 5W-50 in my "beater" car. I hope to have a UOA sometime in the late Fall. I have seen three UOA's on Syntec 5W-50 and they all looked very good. I think this is a good grade to use for an older car or any vehicle that requires a 50 wt. oil. I am not saying to use this (5W-50) in a new car that requires 5W-20! The virgin TBN on Syntec 5W-50 is about 10.5 which is pretty good. I decided to try this viscosity when I noticed the old Prism was just starting to need a little oil added between oil changed and it also was starting to get noisy when it was first started due to engine wear from about 146,000 miles.
 
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8,937
Location
SC
quote:
Originally posted by Dr. T: As far as the VII thing. Let's just say ALL oils have them. How many in the 0-30? The 0-40? 10-60? And the protection afforded by a 50 weight IMHO superceeds the worry about VII's ...
That's the problem. The VI improvers are what's making that oil behave like a 50 wt at high temps, and if they break down or shear off, you don't have a 50 wt anymore. Whereas a 10w30 synthetic that starts off with a high VI base oil to begin with may need little or no VI improver, so you don't get as much vis loss due to shearing of the VI improver.
 
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2,480
We've all seen the "almighty" (cough, cough) super-real PAO synthetic no-VII's 5-30/10-30 M-1 shear down from it's 30 weight even after 1-2k mi.....All oils have VII's...all oils shear. How much? Don't know. Wouldn't it be better to start higher and shear down eg. 50 to a 40 than a 30 to a 20? In either case, assuming the amount of VII's is higher in a 5-50 than a 5-30, are they the only thing that's responsible for a higher HT/HS???
 
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Saratoga, NY
On their site, Red Line showed a graph from a test and they showed a 5W50 (hinted it was Castrol) and the stuff sheared down frightfully while Mobil 1 15W50 held its grade admirably showing almost no shearing. Admittedly, this test/graph is now several years old and probably featured an old PAO formula Castrol ... but the difference was alarming. Nope, I wouldn't use 5W50 in anything I owned. [SPAZ!] Too unstable for a car I cared about, too expensive for an old beater. --- Bror Jace
 
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5,358
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Gone
Dr T, I answered "no," and yes, I have used the 5W50...did I have major problems...no; does that mean something I might not have liked was going on in my engine...no; I used it in ignorant bliss, if you will, not knowing as much about lubrication as I know now...do I like the IDEA of 5W50...you bet...will I use it...huh uh (unless I can get the M1 version). Is that because I think M1 is invincible...no. It's because the more I learn about Castrol, the less confidence I have in it. I'm still convinced many people use Castrol based on the record of its Castor-based oils and not its petroleum products (and because it is "from Europe.")
 
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8,937
Location
SC
quote:
Originally posted by Dr. T: We've all seen the "almighty" (cough, cough) super-real PAO synthetic no-VII's 5-30/10-30 M-1 shear down from it's 30 weight even after 1-2k mi.....All oils have VII's...all oils shear.
Really? How about posting a link to ANY UOA that has shown Mobil 1 shear out of grade in 1-2k miles. [Roll Eyes] As far as all oils having VI improvers, you're just flat out wrong. Ever hear of a straight 30 wt?
 
Messages
658
Location
EU
It may be true that all oils shear, however it is a matter of degree, as I understand it. The question is, then, which oil formulations/viscosity combinations are most prone to shearing. Dr., please educate me on this score. I'd like to see data/studies/analyses, if possible. Thank you.
 
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3,346
Location
Clarksville, Tennessee
well back in the day. When my F150 was new, and I didn't know any better. My first choice was to use Castrol's 5w50. I used this oil at the first change 3000 miles, until I switched to Amsoil at 18,000 miles. I remember running an 8,000 mile drain on it once, I'll have to see if I did an analysis of it. Anyhow, now that I'm educated I would not use a product with that high of viscosity. If I were to choose an oil for racing, I would get something in the 15w40-20w50 area. For passenger cars, anything over Xw30 is robbing HP and fuel economy.
 
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