10W30 can be used but not 5W30. Why?

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I have car manual which says:
10W30. For Ambient temperature -25°C to 30°C
5W30. For Ambient temperature not more than -10°C

This is not the 1st car manual saying such things. Now, my understanding has always been, 5W30 should also be usable up to 30°C but apparently not. Any reason why? BTW, car are not being used in the freezing Arctic.
 
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5w-30 is Resource Conserving here in the U.S. Resource Conserving oil is designed to thin for improved fuel economy. Some 10w-30 are not. Non Resource Conserving oil is required in models that should not run 5w-20.
 
Originally Posted By: jorton
5w-30 is Resource Conserving here in the U.S. Resource Conserving oil is designed to thin for improved fuel economy. Some 10w-30 are not. Non Resource Conserving oil is required in models that should not run 5w-20.


So a 10W-30 provides better protection? I don't understand your answer.
 
Outdated information in the manual. There's no real difference between those two oils near operating temperature.

FWIW, GM specs 5w-30 in all their new cars and trucks for sale in North America.
 
+1. That's outdated information.

Considering today's typical off the shelf oils, I don't see the point in 10w30 anymore.

Joel
 
My Chrysler owner's manual is similar but it allows 5W30 to be used up to something like 20°C

I used 5W30 all last summer when it was regularly over something like 43° C (I think...I haven't used the metric system in a long time.
lol.gif
It was over 110° F) Point being that I have over 120,000km on 5W30 in a high boost turbo Chrysler and it is just fine. So I'm agreeing with everyone in saying that it is outdated information.
 
Originally Posted By: sciphi
Outdated information in the manual. There's no real difference between those two oils near operating temperature.


Not true, most regular 5W30 oils shear down to 5W20 rapidly. Easy to see in most UOA.
 
Originally Posted By: friendly_jacek
Easy to see in most UOA.


Except we don't have a lot of 10w-30 UOAs in similar applications and similar conditions to see if the same thing is happening. In any case, there are plenty of cases where the 5w-30 oils don't shear out of grade. One can cherry pick all kinds where there was fuel dilution, for instance.
 
Originally Posted By: Garak
In any case, there are plenty of cases where the 5w-30 oils don't shear out of grade. One can cherry pick all kinds where there was fuel dilution, for instance.


Mind you, I didn't say all 5W-30 did shear down.
I said most regular 5W-30, meaning non-synthetic. And I didn't just say it. I did a study of BITOG published UOAs a couple of years ago that clearly showed that effect.

You can believe me but you don't have to. I don't care. If you have evidence that most regular 5W-30 oils don't shear down, I would like to see your study.
 
I'm not saying I have a study. I just don't think it's as big of an issue as it was even a few years ago. There are plenty of recent ones where they have not sheared out of grade. There are enough synthetics that have sheared out of grade, too. I'd be interested in seeing how the latest SN/GF-5 conventionals compare to SM/GF-4 in that respect. Also, I'm curious as to whether your study compared 5w-30s to 10w-30s. I'm not saying 5w-30 won't shear, but how much of an improvement does 10w-30 provide?

Personally, I think a lot of it is application dependent. And there certainly are varieties of 5w-30 that are more shear resistant (or perhaps thicker to start with) than others, and I'm sure you're study showed that. Anecdotally, when my carb and engine in the F-150 were bad, ordinary 5w-30 PCMO conventional wouldn't do the trick. The oil pressure light would come on at idle when up to temperature. Max Life synthetic blend (not an overly thick HM oil to begin with), exhibited none of that behaviour throughout the OCI.

My point really is that in certain applications where there is known shearing due to fuel dilution, I don't think a switch to 10w-30 is going to be a magic bullet. For my case, I stuck to the Max Life in the winter and a 15w-40 in the summer.
 
Originally Posted By: Gebo
Originally Posted By: jorton
5w-30 is Resource Conserving here in the U.S. Resource Conserving oil is designed to thin for improved fuel economy. Some 10w-30 are not. Non Resource Conserving oil is required in models that should not run 5w-20.


So a 10W-30 provides better protection? I don't understand your answer.


Heavy duty oil comes in 10w-30. It's not supposed to thin like resource conserving oil does.
 
5W-30 has a lower base oil viscosity and more viscosity modifier than 10W-30. Even though the polymer may have the same shear stability, the 10W-30 will shear less.

SSI or shear-stability index means what percentage of the POLYMER viscosity is sheared - a lower number is better. For engine oils we use the 30-cycle Orbahn injector test to measure SSI. Most heavy duty oils are formulated with 35SSI polymer.

So, a 5W-30 has a base oil viscosity of about 4.5 cst @100C, and is thickened with polymer to 11 cst @100C. If you assume that the real world shearing situation is similar to the Orbahn test, that means your oil will shear to 8.7 cst - (the polymer viscosity is the difference between base oil viscosity and blend viscosity)

A 10W-30 would most likely have a base oil viscosity of about 7 cst and will be thickened with the same polymer to 11 cst @100C (less polymer). This oil under the same conditions would be 9.6 cst @100C

So... you can see where there is a difference in the amount of polymer and shear stability. This is not universally true, as some oils may have more shear stable polymers and heavier, synthetic base oils that have exceptionally cold-flow properties
 
Originally Posted By: jake88
5W-30 has a lower base oil viscosity and more viscosity modifier than 10W-30. Even though the polymer may have the same shear stability, the 10W-30 will shear less.


That will only holds true if both 5w30 and 10w30 uses the same base oil.

But in the market, 10w30 are typically Mineral based whereas the 5w30 or 0w30 are either Semi or Fully Synthetic based. So if we are using 0W30 with Fully Synthetic base oil, shouldn't that be usable to 40C ambient temperature just like the 10w30?
 
Yes, it is true that the type of base oil matters. I think you would be surprised how much of a difference the base oil viscosity makes compared to the difference between mineral oil and isodewaxed oil "so-called synthetic oil". However, PAO and esters really have a noticable effect on the cold-cranking viscosity.

I would expect the 0W-30 synthetic to still have a significantly thinner base oil than the 10W-30 mineral. Generally, the wider the multi-grade the thinner HTHS and base oil viscosity, and more polymer must be added. The HTHS should still be at least 2.9 in either case, though.
 
Originally Posted By: jake88
I think you would be surprised how much of a difference the base oil viscosity makes compared to the difference between mineral oil and isodewaxed oil "so-called synthetic oil".

Care to clarify further? Thanks
 
Well, in the US market there is precedent (in a Castrol case) that an API Group III mineral oil, which is considered to be "isodewaxed" can be marketed as a synthetic oil. If a blend of Group II 4.5 cSt oil and Group III 4.5 cSt oil were thickened to the same amount, their cold temperature properties would not be as drastically different as a 4.5 cSt blend of PAO thickened identically.

This is because the Group III oil still contains waxy molecules, though many of them have been busted up by severe hydroprocessing. PAOs and POEs are more branched than Group III oils and thus do not form the same crystalline structures that cause pumping and cranking issues.

So, getting at the point of the question, given a synthetic blend 5W30 and 10W30, the 10W30 is likely to have higher viscosity at operating temperatures because the oil starts out thicker and relies less on polymer thickening (so it is more shear-stable). Does that clarify anything?
 
In general terms for new diesel engines from Germany they seem to be recommending 0/30 fully synthetics. It was 5/40 for similar engines only 10 years ago, but the recent models are OK if the oil shears down to a 20, so they dropped the 40 to a 30 at the top end as a narrower range oil will last longer due to the different additives package.
My guess as to why the cold viscosity figure has changed from the more obvious 5 which would be better for cold starts to a 10, is that the additives last longer at lower temps, so the oil change interval can be extended as a result, which I think is rather silly as if they have that kind of TBN issue it would be better to use a 0/30 and sling in a can of approved additives after 10k of half the distance etc.
 
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