5W30 10W30 shearing

[GMorg]

I keep reading recommendations to use 10W30 rather than 5W30 in warm areas/times due to less shearing. Historically, I would have accepted that recommendation. However, from used oil analysis here, I have not been able to confirm that the difference is still there. It seems that both less VIIs are being used in modern oil and that those that are being used are more shear stable.

So, is the above recommendation still valid? If so, does it only apply to mineral based oils? Many synthetics appear to completely free of VIIs.

 

[Dagwood]

Do a search and you will find a good amount of information on the subject of shearing. The recommendation of using 10w30 instead of 5w30 due to the possiblility of shearing is really a dying concept. Examine some used oil analysis and you will see that while there is still some shearing out of grade, it is not as relevant as years ago. Follow your owner's manual and your engine will outlast the rest of the components in your vehicle.

 

[Eddie]

Agree 100%

 

[Bryanccfshr]

I don't think it is still a valid point. Perhaps the only difference is the amount of pour point depressants used to meet the 5w rating. The current 5w30's on the market usually have more manufacturere specifications to meet than the 10w30's whichn are starting to go the way of 10w40

 

[XS650]

That's mostly history. I would still stay away from El Cheapo 5w30, but I stay away for El Cheapo oil in general so it's not an issue with me.

 

[Ray H]

I suspect the 10w30 viscosity grade will remain viable in hot climates as long as it can meet the API "Energy Conserving" designation. 10W-40 will likely remain available as the "beater" grade oil of choice where high oil consumption is an issue.

 

[GMorg]

JAG,

I can see a general correlation between MW/size and volatility (though there are many significant exceptions). However, I am completely missing the correlation between MW and chemical stability. What am I missing?

 

[addyguy]

I had a very brief look at 5w30 conventional and 10w30 used oil analysis in the used oil analysis forum. There seems to be no difference between the two grades - both shear almost equally back to a low 30/high 20-weight in anywhere from 2-5,000 miles.

So no, recommending one over the other doesn't make sense......

 

[hominid7]

It would seem to me that 'temporary shear' would be greater in 5w30's due to greater amounts and larger VII molecules.

However permanent shear differences between 10w30 and 5w30, since GF-4 came out, would be similar.

Some 10w30's have the same vis numbers at 100*C as their 5w30 counterparts, but in some brands the 10w30 appears to be 'thinner'. My guess is that the 'thinner' 10w30's are actually less prone to permanent shear than the 10w30's that are equal to their 5w30 counterparts.

I go back and forth as to which to use, 5w30 or 10w30. Right now i'm using Pennzoil Conventional 10w30 and have been very happy with it. My car does not feel sluggish as it did with other thicker 10w30's, but it does not have the valvetrain noise it did with 5w30.

For the record, my Mazda is spec'd for 5w30 at temps below 30*F and spec'd for 10w30 for temps above -15*F.

Ford puts 5w30 in year-round in this Mazda engine, but Mazda sticks to it's orig recommendations. Go figure...

 

[GMorg]

addyguy,

Wether sheared or diluted, I came to the same conclusion.

However, I am still pondering surfstar's and JAG's position. It is not clear to me where minor NOACK, HTHS, or Volatility differences will come into play on a seasonal basis. I am open to any clarification that anyone can provide.

 

[JAG]

GMorg, I searched to no avail. Maybe my memory failed me, so I take back the correlation between MW and chemical stability comment unless someone can confirm it. As you said, the volatility correlation is certainly true.

 

[surfstar]

California has only one season, so its 10w30 year round for me

 

[GMorg]

surfstar,

Touche'

 

[GMorg]

JAG/surfstar,

I don't want to pester, but can you elaborate on when the 5W vs 10W differences are particularly important for a 30 weight?

 

[bruce381]

quote:

---

Originally posted by GMorg:
JAG/surfstar,

I don't want to pester, but can you elaborate on when the 5W vs 10W differences are particularly important for a 30 weight?

---

when its cold
out

bruce

 

[surfstar]

For a given brand 10w30 has better NOACK and HTHS numbers than the equivalent 5w30 - I prefer it mainly for this reason.

 

[JAG]

surfstar is on the right track. The fundamental chemical truth that influences motor oil so much is that for a given molecular structure, the longer/larger the molecule is, the less volatile and more chemically stable it is. Shearing isn't the issue because engines do well on a pretty wide viscosity range.

 

[GMorg]

Bruce381,

I can see why you may want 5W for the cold. My curiosity is related to why one may feel the "need" to use 10W in the summer. I don't mean historically, I am making reference to current oils.

 

[JAG]

GMorg, I wouldn't say it's a need but it can be preferable. My VW 1.8T engine's oil abusive behavior has warped my viewpoints on how good oil should be. The intercooler eventually gets a decent sized puddle of oil sitting in the bottom of it from the crankcase ventilation system routing the oil vapors to the intake. A little puddle also forms at the beginning of the throttle body. This just goes to show how much oil vapor there is even with very low volatility oils. Burning oil through ingestion as if it is air or fuel (as opposed to burning the layer on the cylinder walls) is bad on all counts. It reduces the effective octane of the A/F mixture and creates extra abrasive ash in the combustion chamber/on valves. The cat. convert. also gets more phosphorus poisoning. On a turbo engine, you don't want the octane to lower at all because it's on the threshold of detonation already.

Then there's usually a HTHS difference as well but I think this matters only if you have an engine that is designed for a high HTHS oil, like many Euro engines. 10w30 would probably not be ideal viscosity grade anyway for many of those engines (might get consumed at excessive rate if the engine calls for a 40 weight).

As you know, a top notch 0w30 can have lower volatility and higher HTHS than a 10w30 synthetic, so I don't want to sound like I'm afraid of the 5w30 spread. You have to look at the properties of the oils in question because there are exceptions to the trends.

 

[GMorg]

Thanks