For Corvette C6, Z06 owners, many of the U.S. guys like to use is what they call, the 0W40 Euro blend Mobil 1, rather than following GM’s U.S. Corvette recommendation of using 5W30 Mobil 1. The 0W40 oil is what GM calls for in the Owner’s Manual and also on the oil filler cap on C6 Z06's sold in Canada and Europe. And many people think they know better than the Engineers who designed and built their cars. But, perhaps they should consider the following.

Let’s take a look at what is specifically going on with motor oil during cold start-up vs what is going on with it at hot operating temperature. And keep in mind, EVERY motor oil thins out as it heats up and thickens as it cools down, no matter what its identifying multi-viscosity rating might be.

For this comparison purposes, multi-grade motor oil viscosity properties are typically given at 40*C (104*F) and at 100*C (212*F). And its thickness is given in an accurate measurement called centistokes (cSt). The HIGHER the cSt value, the THICKER the oil.

The cold 40*C (104*F which is only slightly above normal temperature for humans) temperature shown below will be used to represent cold start-up conditions, though at more common colder temperatures, the oil will be even “thicker” yet. And the hot 100*C (212*F) temperature shown below will be used to represent hot operating conditions, though at more common higher temperatures, the oil will be “thinner” yet.

Typical Examples of Actual Motor Oil

cSt @ cold 40*C (104*F) / cSt @ hot 100*C (212*F)

0W20 = 44.9 / 8.5, or 5.3 times thicker when cold

0W30 = 53.8 / 9.6, or 5.6 times thicker when cold

0W40 = 79.9 / 14.3, or 5.6 times thicker when cold
-----
5W20 = 51.6 / 9.0, or 5.7 times thicker when cold

5W30 = 62.4 / 10.8, or 5.8 times thicker when cold

5W40 = 87.2 / 14.7, or 5.9 times thicker when cold
-----
10W30 = 71.8 / 11.5, or 6.2 times thicker when cold

10W40 = 96.5 / 14.7, or 6.6 times thicker when cold

10W60 = 168.5 / 24.1, or 7.0 times thicker when cold
-----
15W40 = 105.0 / 14.8, or 7.1 times thicker when cold

15W50 = 133.8 / 20.2, or 6.6 times thicker when cold
-----
20W50 = 170.0 / 20.2, or 8.4 times thicker when cold

Notice how the thickness of the hot viscosity rating (the number AFTER the W) of any given oil above, also affects the thickness of the cold viscosity rating (the number BEFORE the W). For example, 5W20 and 5W40 both have a cold viscosity rating of 5, but the cold thickness of 5W20 is 51.6 cSt, while the cold thickness of 5W40 is 87.2 cSt, or 1.7 times thicker when cold, even though they both have the same cold viscosity rating of 5.

And as you can see above, even at these modest cold and hot temperatures that motor oil thickness values are typically available for, the oil is WAY, WAY THICKER when cold, than it is when hot. And the difference is even GREATER at more normal colder start-up and hotter operational temperatures. So, that means that at cold start-up, oil flow rate/lubrication will be GREATLY REDUCED, even if you are using the recommended multi-viscosity motor oil. But even so, multi-viscosity oils are still a good thing, because they would be even thicker yet when cold, if they were straight wt oils.

And this will likely surprise a lot of people. Notice that cold 5W20 at 51.6 cSt, is 2.6 times THICKER, than hot 20W50 at 20.2 cSt. Now you know that a low viscosity cold rating does NOT mean the oil is thin when it’s cold.

So, all this brings us back to 5W30 vs 0W40. Looking at the viscosity list above, you can see that, as expected, 0W40 at 14.3 cSt when hot, is definitely thicker than 5W30 at 10.8 cSt when hot. In fact, 0W40 is a whopping 32% thicker when hot.

Now let’s compare them when cold. As you can see above, 0W40 at 79.9 cSt when cold, is definitely thicker than 5W30 at 62.4 cSt when cold. In fact, 0W40 is a substantial 28% thicker when cold, even though it is rated as a “0”wt when cold, which most people would expect to be thinner than a cold rated 5W. So, once again, you can see that the thickness of the hot viscosity rating, also affects the thickness of the cold viscosity rating.

People who thought that their 0W40 was thinner than 5W30 when cold, are unknowingly off-track. But, they now know that their 0W40 is NOT flowing better than 5W30 when cold. In fact, their 0W40 is flowing considerably “worse” than 5W30 when cold. Technical matters are often not as simple as they might seem at first glance.

The 5W30 flows better/quicker during cold start-up, to reach critical engine components quicker to prevent wear. And since cold start-up is where 90% of engine wear takes place, the thinner the oil is when cold, the better.

And of course 5W30 also flows better when hot. Better flowing thinner hot oil, lubricates better, cools better, releases bubbles/foam better, and let’s an engine produce more power by reducing pumping losses and viscous drag. So, if you are interested in providing your engine with the best possible motor oil protection, you want the superior 5W30 which is better when hot and better when cold.

So, GM got it right when they called for 5W30 in U.S. C6, Z06 Corvettes. Something to consider the next time your change oil.

540 RAT

Mechanical Engineer

U.S. Patent Holder (Mechanical device designed for Military Jet Aircraft)

Member SAE (Society of Automotive Engineers)

Member ASME (American Society of Mechanical Engineers)

Lifelong Gear Head, Mechanic, Hotrodder, Drag Racer, and Engine Builder

For the truth about motor oil wear protection, that is not just opinion or theory, see my "TECH FACTS, NOT MYTHS" Blog, which now has over 295,000 views worldwide. You can see the Blog and my entire 199 motor oil “Wear Protection Ranking List”, which is "proven" by the Physics and Chemistry involved, and EXACTLY matches real world severe over-heating experience, real world Track experience, real world flat tappet break-in experience, and real world High Performance Street experience (test data validation doesn’t get any better than this), along with additional motor oil tech FACTS, by going to the Blog link below. Methodology, proof, facts, data, Industry endorsements, real world validation, etc, are all included in the Blog. See for yourself, the engine you save may be your own.

http://540ratblog.wordpress.com/

 

Great info...Thanks. ....WW

 

Is there a short version to this?

 

Use what is on the oil fill cap.

 

So why is 0w-40 recommended in other countries?

 

This a very informative post. Many thanks to the OP for this. I have been an avid reader of his blog for some time now. I've always found it amazing that the advertised viscosity ratings on motor oils really don't accurately indicate the viscosity of the oil in the bottle. I don't think that most folks appreciate this. In a way, it's a form of false advertising, in my humble opinion.
One thing of interest that I've recently noted from the OPs testing of Mobil 1 5W30 vs. Mobil 1 0W-40 (Euro spec) oil is that the latter is much more resistant to thermal breakdown at elevated temperatures (~275*). Therefore, it may be a better oil for those of us who do road course/autocross racing where temps can get up into that temperature range.
For me, I'll stick with the 5W-30 with my stock bottom end and high volume oil pump, because I have more than enough pressure and I think that's what these engines were built for.
As far as why the 0W-40 oil is specified for the European market, I've been puzzled by that too. I wonder if this could be because the engines are built with different clearances for the euro market, if that us even possible? Or is it just a marketing ploy, because I've noted that manufacturers like BMW likes to specify thicker grade oil for their performance cars?
We have been having another discussion on another thread on this forum about a member who has a built engine with looser clearances and, consequently, lower oil pressures, and it clear that some folks thinks that whatever the factory recommends is the what should always be used.
This all reminds me that what folks need to know to decide on what viscosity oil they need to run is in fact the clearances of their engine. That's not to say that I agree with the old school train of thought that looser is better and you should just run a 40-50wt oil to keep pressure in the oil galley sufficiently high to keep an oil film on the bearing surfaces.
In the end, you need to know what your engine needs. No doubt GM has done a fair bit of research on this, because the liability from a factory warranty would dictate that's necessary.
But I'm still curious as to why they recommend the 0W-40 for the European market, if that's in fact the case?
Thanks again to the OP for sharing the benefits of his expertise on here.

 

How about stock bottom end LS7 that lives in the 235* - 245* range on track most of its life ??
0w40 ??
15w50 ??
.
.

 

It's quite possible, because 0W-40 has significantly more phosphorus than the 5-30 blend.

 

You might be on to something there. I live with one, so I know exactly what you mean!

 

235-245* isn't that high of an oil temp, IMV. I'm no expert on this stuff, by any stretch of the imagination. But I wouldn't run 50 weight oil on a stock LS bottom end.
I think the best thing would be to put a good engine oil cooler on it to keep temps from getting up past 240* or so.

 

Very interesting I think also depends on the type of oil and its use. 540 Rat did a test on some Mobil 0-40 and it had a very high - good squish factor of like 100,000 psi or something like that - I think it was like #2 or #3 on his ranking list which is very extensive.

 

What our engineer friend failed to state was Its an emissions/EPA thing only. All 30w oils can only have so much zinc (converters), anything 40w and up isn't regulated so tightly and thus has more zinc added.
Why some guys run 0w-40 is because it will obviously protect your engine far better when pushing it harder or in hot environments.

Retired glorified used car salesman
School dropout

 

Since it's obvious to you, can you share proof of this statement?

 

No, other way around
0W-40: 1000ppm Phos, 1100ppm Zinc
5W-30: 800ppm Phos, 900ppm Zinc

M1 product guide attached

M1 0W40 in everything (including the lawnmower) for me. Good stuff.

 

Anyone wanting to know more about this topic should read the OPs blog, particularly the test results. The 0W-40 Mobil 1 Euro spec oil is the top performing oil without any additives - the only two that surpassed its shear or wear protection rating had Prolong oil treatment added. At normal oil temperatures, it has nearly 10,000psi of wear protection capability over the Mobil 1 5W-30 dexos oil, which is still an outstanding oil (and what I use myself for my SBE LS3). But when the two were tested at 275* oil temps, the 5W-30 oil experienced greater thermal breakdown, losing 36% of its wear protection capability vs. the 0W-40 only losing 16% at the same temperature.
So, based on the OPs testing, the 5W-30 is not "as good" as the 0W-40 at any temperature, in terms of wear protection, particularly at very high temperatures.
But, that doesn't make the 0W-40 the "better" oil for a stock bottom end C6, which is something the OP also points out in his blog.

 

Yes, agree, 0W-40 is better on the track. I have a C6Z, and I can barely get the damn oil up past 180* on the street, even driving really hard. So 5W-30 suits me just fine, and will work great for 99% of us street drivers.

EDIT: This statement from the OP is what sells me on using 5W-30:

"The 5W30 flows better/quicker during cold start-up, to reach critical engine components quicker to prevent wear. And since cold start-up is where 90% of engine wear takes place, the thinner the oil is when cold, the better."

I live in the north, so cold starts are the norm. Having thinner oil at startup is critical to me, as that's where all/most of engine wear occurs. The OP is right, people thinking that 0W-40 is thinner when cold than 5W-30 now know better. It's not. Not even close.

 

You just admitted it yourself in post #16

 

Yep! My bad. Dyslexia strikes again. !aH !aH

fixing the fu

 

Admitted what? At very high sustained temperatures on a track, yes, the 0W-40 starts to benefit the engine. In every other situation, it does not, where most of us live (99% of us are street drivers). I was asking in context of normal street driving.

5W-30 is better on cold startup. By a lot. That's where most of all engine wear occurs. If you race your car all the time, by all means, use 0W-40. If not, and you still use it, you're putting your engine through more wear at startup than 5W-30.

Did that not come across clear in the OP's post?

 

I suggest those who believe that the zinc content is the determining factor of wear protection go read 540RAT's blog. Zinc content is all over the place on the rankings of motor oil and wear protection.