Mobil 1 0W-40 abuse

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Sep 25, 2002
Loveland, Colorado
There are some ugly rumors going around that M1 0W-40 can't "make the grade" the way other oils do. Well, I'm here to stand up for an oil which needs no support, but can't defend itself because it has no fingers with which to type.

It's not really a question of, "Did it stay in grade?" so much as, "How much did it thin out?" And even then, it needs to be taken in the context of the engine it's being used in. I took the liberty of sifting thru a few of the UOAs & came up with some interesting data.

First of all, this oil is the single most popular oil for turbo owners, at least in terms of the data we have here. Of the 13 full syn UOAs I used, 4 were for M1 0W-40, or 31%. The other 6 oils were divided up with only 1 or 2 UOAs apiece. Unfortunately, this means the data's not very relevant for any of them yet. I also found 1 UOA for Castrol GTX in a turbo & 2 UOAs for M1 0W-40 in non-turbo applications, just for more statistically-irrelevant comparisons. I didn't look at UOAs which were less than 4k miles, since most of us agree that, even with the accelerated abuse a turbo gives oil, any full syn should survive for that short of a duration. I also didn't include any BobZoil numbers, simply because I couldn't find fixed VOA cSt numbers (only cSt ranges listed on the oils' data sheets). Most of the turbo engines were the VW 1.8T, with a few Volvos & one Subaru.

Also, due to lab variances & the fact that VOA cSt numbers weren't available for the M1 5W-30, Amsoil 5W-30, & Amsoil 10W-30, I decided to use virgin cSt numbers pulled from manufacturers' data sheets for as many of the oils as I could. I used VOA cSt numbers for Lubro Moly, RedLine, & Castrol.

M1 0W-40, 4 samples:
Baseline cSt: 14.4
Avg mi: 4998
Avg cSt: 12.3
Avg change: 14.6% thinner
Best mi: 4764
Best cSt: 12.8
Best change: 11.1% thinner

Lubro Moly 5W-40, 1 sample:
Baseline cSt: 14.0
Mi: 4100
cSt: 12.4
Change: 11.4% thinner

RedLine 5W-40, 1 sample:
Baseline cSt: 15.7
Mi: 5000
cSt: 14.6
Change: 7.0% thinner

M1 5W-30, 2 samples:
Baseline cSt: 9.7
Avg mi: 4463
Avg cSt: 9.8
Avg change: 1.0% thicker

Amsoil 5W-30, 2 samples:
Baseline cSt: 11.7
Avg mi: 4950
Avg cSt: 11.6
Avg change: 0.9% thinner

Amsoil 10W-30, 2 samples:
Baseline cSt: 11.9
Avg mi: 5565
Avg cSt: 12.0
Avg change: 0.8% thicker

Amsoil 20W-50, 1 sample:
Baseline cSt: 18.4
Mi: 10,000
cSt: 11.8
Change: 35.9% thinner

Castrol GTX 5W-30, 1 sample:
Baseline cSt: 10.6
Mi: 1350
cSt: 8.8
Change: 17.0% thinner

M1 0W-40, non-turbo, 2 samples:
Baseline cSt: 14.4
Avg mi: 8562
Avg cSt: 13.8
Avg change: 4.2% thinner

So what do we know? That non-syn oils shouldn't be used in a turbo, & M1 0W-40 can go 10k miles easy in an NA engine. Maybe it's better to ask what we don't know. For example, these numbers don't show that both of the Amsoil 5W & 10W samples had 1 thining & 1 thickening, averaging to a nearly balanced result (the 5W-30 had a 17% variance between the 2 samples, while the 10W-30 had a 5% variance). In contrast, all of the M1 numbers were consistant (all the 0W-40s thinned, while the 5W-30s thickened). Does this mean that Amsoil's less predictable? Again, we don't have enough data. Is oxidizing better than shearing? I don't know.

Here are my opinions for a turbocharged engine:
1) The "used" viscosity of M1 0W-40 is more desirable to me than "used" M1 5W-30. (Actually, more so than any of the M1 30wts, since they all start out lower than the 0W-40 ends up.)
2) The price & availability of the M1 0W-40 is more desirable to me than any of the "boutique" brands.
3) [There is no 3rd thing.] (Sorry, but I had to get Monty Python in here somehow ...)
4) Saying that a "thick" 30wt "stays in grade" but a "thin" 40wt doesn't, should now mean the same as saying "Blue oil is sweeter than pre-chewed eucalyptus leaves."

Give me your opinions on all of this, & let me know where my analysis is flawed.
Did I miss this abuse? Dang....

Honestly I must have missed that thread. I certainly was not thinking about M1 0W-40 in that manner.

The interesting thing to me I'm the only idiot that went 10K on my turbo with the 20W-50!!! And sorry as this sounds: Glad it did thin a bit....well OK a LOT!
Pablo wasn't that from fuel dilution though? The thinned out 0w40 are not...

Don't know why people wan't to defend a oil that consistently shears so much. But that's why we live in America. It's your engine, not mine (Thank God
Jason - I couldn't remember so I found the post. I really did forget that my wear numbers were so low...but the oil got relatively thin....

The fuel was 1.1% - not great, but not super high - they (OAI) did flag it that I do recall.

You guys are gonna REALLY hate me now. I'm coming up on 10K on this car again....and well I changed my filters mid interval...and well I didn't have any 20W-50...I thought I did...and I had already dropped the old I prefilled the filters and topped up with Amsoil 5W-30. Insane yes. Experimental? That's me....but it sucks because the vis numbers will be bizzare...spank me.

Gotta finish the 20K testing on the other Volvo first, though.
I don't see the thinning as that big of a deal. I'd use it if it were cheaper. For $1/qt more you can get one of those expensive "boutique" oils that hold up better.

You should be looking at the change in the HT/HS viscosity, not the low shear rate or kinematic viscosity @ 100C. Respective HT/HS viscosities for Mobil 1 are as follows:

5w-30, 3.1 Cp
10w-30, 3.2 Cp
0w-40, 3.6 Cp

The 0w-40 shears by an average of 15%, so the HT/HS of the 0w-40 is going to end up about 2.8 Cp, assuming a one to one correlation between change in kinematic viscosity @ 100C and HT/HS viscosity @ 150C. The HT/HS viscosity of the 5w-30/10w-30 is going to stay at or above 3.0 Cp for the entire drain interval, even in a turbo. So the performance of the 5w-30/10w-30 is more consistent over the entire change interval.

I'd rather use the 5w-30 or 10w-30 in that case, even if we are just comparing the various Mobil 1 formulations ....A shear stable, 10w-30 like Redline with a HT/HS of 3.5 Cp or so would be preferrable to both of these, IMHO.

Degradation of polymers also results in sludge/varnish formation inside the engine over the course of a long drain interval, so the 10w-30 is going to run cleaner.
you guys are ignoring the fact that turbo engines ARE harder on oil. The last item on his list of viscosities is non-turbo applications with an average of over 8500 miles. And yes, they did remain a good bit inside the 40wt range. Thinning an average 4.2%, which is lower than all the other oils other than Amsoil 5/10w30 with less mileage on them. Mobil1 0w40 is probably one of the best over the counter oils you're gonna find. It's wear numbers are good and in NA applications and it does stay in grade.

I am anxiously awaiting Vader SS's next 0w40 UOA, as his Impala SS uses basically the same LT1 engine as the one in my Firebird (his has iron heads while mine has aluminum heads, and I believe his cam is different too)

I don't believe his first UOA showed this oil thinning out all that much, so his would be a good example of a hard driven non turbo car running this oil.

I'll admit, I've been disappointed (and mentioned it here) with how 0w40 thins out, but in reality there aren't many 0w40 oils out there to compare it to either. That is a pretty big spread for an oil to achieve, so I guess some thinning is expected, unless it's a $15 per quart oil with one heck of a good base oil. We are talking about a $4 oil here, so put into that context, it does make it look more impressive.

I'll try to keep my 0w40 bashing to a minimum from now on.
Isn't it funny how we all root for certain oil brands and grades like sports fans root for their teams! Freud would have a field day here.


The 0w-40 shears by an average of 15%, so the HT/HS of the 0w-40 is going to end up about 2.8 Cp, assuming a one to one correlation between change in kinematic viscosity @ 100C and HT/HS viscosity @ 150C.

Would the HT/HS change at all since the HT/HS is the sheared viscosity anyway? That's why they shoot the oil through the diesel injector right?--to shear it? At any rate, 15% of 3.6 is 3.06.
Wouldn't it be safe to assume the engineers designing the engine and specifying the oil are aware of Mobil 1 0W-40's behavior over time? I'm sure they care less about the viscosity slightly thinning at 5000 miles compared to how well the engine components are holding up. The auto manufacturers perform durability testing under extrememly harsh conditions as part of their development programs. If the oil works under these conditions well enough to be qualified, and you believe the manufacturer truly wants their customers to be satisfied with the longevity of the engine, what's the concern?

I own a turbo engine with Mobil 1 0W-40 as OEM fill and I'm comfortable relying on the manufacturer's oil recommendation based on their test programs. Could you get an extremely small incremental increase in the durability of the engine from a boutique oil? No one will ever know because of the cost to perform the full slate of testing done by the auto manufacturers. If the cost / benefit for a boutique oil was favorable, Mobil 1 0W-40 would be history.

just my 0.02 worth ...

Originally posted by Jay:

At any rate, 15% of 3.6 is 3.06.
Yes it was ROUGHLY gauged on the not to favorable side to and the end result at that rate is near to none oil film left.

Mobil has themselves a good oil there. My hats off to them for making it available to us at such low cost and it's available everywhere ! It has a lesser additive package than the 10/30 so I do believe it rely's a bit more on Esters intstead of VII's than it's siblings the 10/30 and 5/30 .

Greg Netzner thank you for taking time to do the math
"Wouldn't it be safe to assume the engineers designing the engine and specifying the oil are aware of Mobil 1 0W-40's behavior over time?"

RobY, don't bet your engine on that assumption ! Depends on the company and when the bean counters yanked the engineers back to re-engineer things, "slice and dice and repackage "as I call it.
Exxon Mobil is big and powerful and has lots of sway on car companies with premier brands.

Brellaum you may be on to something as far as levels of esters, I just despise any lube that tells me to expect a SAE grade then cannot deliver over a interval.

I'm an equal opportunity lube brand cynic, I distrust them all the same.

I wonder what Freud would say about that ?

That is a pretty big spread for an oil to achieve

I think Patman's right in the fact that the spread is so great there aren't many oils that wouldn't thin out with this spread.

There are no other 0w-40's that I know of too compare it too, but look at Amsoil's S2000. According to Terry, it thickens up to a 40wt. after short use. They also claim that you should get better MPG with S2000 and I havnt found this. Being it thickend to a 40wt. oil would lead me to believe I was achieving worse fuel efficiency.
I think Mobil formulates there oils on the light side for fuel efficiency reasons. I just picked up a case of there 0w-30 and I am going to run it to 8k miles to see what happens. I also think I will get better gas mileage with this over S2000 due to it's lighter wt.

[ February 27, 2003, 05:40 PM: Message edited by: buster ]

You hit the nail right on the head ....

It is not possible to make a shear stable 0w-40 or 5w-50, even with very high quality basestocks and VI improvers. If you really need a shear stable xw-40 synthetic, try Delvac 1, 5w-40. It will perform much better than this in terms of shear stability. Delvac 1 has a VI of only 167, compared to 185 for the 0w-40. The difference is that Delvac 1 isn't loaded up with polymeric thickeners ....

Of course Mobil knows about this shearing - the test data in their SAE paper # 981444 clearly shows this effect in standardized engine tests.

The polymer shearing helps these 0w-40 synthetics pass the fuel efficiency requirements that are part of the Mercedes 229.5 specification. It also helps them stay in grade over very long change intervals by first thinning out by 15%-20% and then thickening back up. All the 0w-40's will do this to some degree ....
Thanks for all the replies so far! Let me address a few items at this point.

Pablo, maybe I'm just hyper-sensitve to any off-color comments, since I feel this is a "best buy" oil for my turbo. And just so you know you're not alone, I'm also running my turbo to 10k mi intervals. The previous 2 intervals were on 10W-30 Syntec, & the current one's on the 0W-40. I didn't care to have the Syntec analyzed, & my 5k M1 UOA is still about 4mos away.

satterfi, maybe I'm just hyper-sensitive to any... oh, wait... never mind. You're right about price, sort of. Yes, I can get the Amsoil 5W/10W-30s for about $1.25 more per qt if I buy enough to do 3 changes at once. But I can't just pick up an extra bottle on-line for that price (it jumps to $5.60 more per qt). The local RedLine distributor will sell me their stuff for $3.00 more per qt than M1, & I can get Lubro Moly for about $3.15 more per qt than M1. I don't mind paying more to get more, but I'm not sure there's enough increase in protection to warrant the extra cost & trouble.

Ted, I agree, HT/HS is the more important number, but none of the UOAs list that, & I don't have the HT/HS numbers for all the oils in question (& where did you get the M1 HT/HS numbers, anyway?). And cSt is what everyone talks about, right? Now, when I multiply 3.6 x 0.854 (the 14.6% avg vis drop), I get 3.1 Cp, not 2.8. Am I doing something wrong? Also, I don't feel there are enough samples of any of the 30wts to be meaningful. I can take a single example of the 0W-40 only thinning by 11.1%, & all the numbers improve accordingly. (And then there's that 17% variance between the 2 Amsoil 5W-30 samples. One thinned by 9.4% while the other thickened by 7.7%.) Don't get me wrong, I think there are better oils available. I just feel the 0w-40's a great choice.

Green Max, I only compared the oils I could find in our UOA section. I wanted to narrow the search to turbo-abused oils, so I searched on "0W-40" ('cuz that's what gets slammed for thinning), "1.8T" ('cuz I knew there were a lot of'em UOA'd), & "turbo" (to see what else showed up). No 0W-30s came up in the search. I also considered including diesel oils, but eventually just decided not to.

Additional data:
The 2 NA cars were a '96 LT1 Impala SS run to 7123 miles, & an '02 3.4L V6 Toyota Tacoma run to 10,000 miles. It was the Tacoma's engine which beat up the averages on this combined example.

I have no problem with the Mobil 1, 0w-40, in fact I think it's one of the best $5.00/qt oils out there. My issue is with the shear stability of 0w-40/5w-50 oils in general over long drain intervals, or in demanding applications. If you had an application where you really needed a mid range 40wt or 50wt - like for a motorcycle or marine inboard engine - a 10w-40/20w-50 synthetic would be a better choice.

This engine runs fine on the Mobil 1, 5w-30, so the fact that the 0w-40 shears isn't going to matter. If the 0w-40 starts @ 3.6 Cp and ends up at 3.1 Cp, I suppose in theory it provides some additional protection over the 5w-30. I think you'd be hard pressed to quantify it with oil analysis though, since so many variables affect the results.

I predict that when you test the 0w-40 in your SAAB after 10k miles, it will have thickened back up very close to it's initial viscosity. I bet it comes in @ approx 13.5 Cst, +/- 0.3 Cst. The thickening effect of oxidation/nitration tends to offset the shearing of the VI modifier. This behavior is well understood - I see it all the time.

Originally posted by Dr. T:
RobY, just curious, but which turbo car comes factory fill w/ 0-40 M-1?

All Porsches come factory filled with Mobil 1 0w40, including the turbo models.
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