Same (basic) question I ask when people question a 6cSt vs 4cSt ATF use.
Lets put 5W-40 in everything...
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Indeed, because Dr Rudnick's wear modeling also makes it quite clear that the HTHS role is only consequential once you're into full film EHD (elastohydrodynamic) lube. If you're at boundary/mixed lubrication (BML), HTHS cannot save you.
Thus, the overall ideal viscosity comes down to the fraction of time your engine will spend in EHD vs BML. The longer your oil pressure delay, the more the total balance shifts. For example, in my Accord's usage as a mostly-loafing commuter with no bitter cold starts (and the cold starts that happen are few and a small fraction of total usage), the startup consideration is only 30% of the total wear budget.
Contrast that with the use case of my Dad in ND, whose daily morning commute start can be -10F. In his case, the cold start delay to re-establish EHD shifts the BML portion of the wear budget to be nearly 80% because his car see essentially no usage other than a cold start followed by a 30 min commute at expressway speeds.
So-- within the part of the wear budget that HTHS matters (EHD), then HTHS really does move the needle. Worst vs best could be 35% difference or more. (say, 0w-20 vs 20w-50). But if that EHD portion is not the predominant part of your application and you oil delays >2.5 seconds as a large fraction of your usage, the BML dominates and HTHS doesn't matter that much.
Thus the adage "as thin as necessary, as thick as possible."
When in BML for a cold start, however, things like having 600ppm moly (HPL oils) can cut wear during BML that it's a net win vs a slightly thinner oil. For example, at 10F, my 15w-40 HPL with 600+ ppm of moly will actually have a good bit less startup wear than than a 5w-30 with no moly in it, because that temperature is not cold enough to cause the 15w to have excessive delay such that the moly doesn't save you.
But at -15F? My 15w-40HPL is going to have enough delay in film recovery that a 0w-30 ESP or 0w-40 Euro FS will far outperform my 15w-40 significantly in cold startup wear. This, even though the ESP has only mid 70s ppm for moly and the 0w-40FS has only a tiny bit more.
Thus, selecting the best oil must necessarily include use case and duty cycle. If all you do it slow off road trails in hot weather or cruise the highway with the engine running hours on end with never any starts below freezing, grab some HPL 20w-50 and never look back-- crushes the 0w-40FS even in hot wear protection because of the monster HTHS while running super clean because of low aerosol generation and super low volatility (25% or so better wear protection than the M1)
Conversely, if you rarely get the privilege of sustained highway runs, you have brutal ND winters as your daily grind, and you idle very little, the 0w-30 ESP will outperform the 0w-40 FS by about 10% in terms of wear rates. By excelling in the super cold starts that dominate the duty cycle, ESP will best protect that particular use case because it takes less time to re-establish EHD films when super cold-- a difference hidden by the 0W ratings of both oils. (they both meet 0w but do NOT have the same cold oil pressure delay!).
This is why I say that 0w-40 FS is pretty close to a universal oil. Because even in the use cases where it's outperformed, it still does pretty darn good, close enough for most people.
And of course, if you want to triple down on that logic, the HPL Premium Plus PCMO in 5w-50 is probably the truly universal oil for all of earth. The super low pour point of -67F, the high moly content (~450ppm), the high TBN (13.5) capped off by the high HTHS (4.7) make this probably the ultimate "one oil" for everyone. Protects well in BML, flows better cold than many 0ws because of the PAO base, but then shows up to the party with amazing oxidation resistance and an HTHS of 4.7 that lasts.
I'd run that Premium Plus PCMO 5w-50 even in Alaska because it will tolerate very well all the idling that is an inevitable part of living in extreme cold. And yet that same oil can go the distance in Death valley all day every day. Very, very few oils could do that. This particular oil has such an extremely wide performance range that even at its worst it's still pretty close to a highly specialized blend tailored to that niche.
It's not cheap, but if you could buy a pickup truck that would turn track times like a GT3RS, it would also be pretty expensive.
not really engine dependent so much as application dependent. See my post above. There are exception to this, of course (turbo vs not, flat vs roller cams, etc).
I noticed with manual transmission toyota with yamaha heads and simple hydraulic phaser on intake cam in the mid 2000's. Talking operation after the vehicle is near or at operating temperature in open loop. Not bench racing but repeatable in-seat experience.
Cam position will be more retarded than design intent at lower rpm affecting torque production. Not a noticeable issue at higher rpm/ steady state highway speed.
Not Kidding around - Arco
I thought the same about cylinder deactivation especially when the lifters were demonstrated to me. However it did work without drama in a 5.3 V8.
Another recent post said 5W30 was the all purpose, go to oil, now the debate is 5W40 on this post. So, which is it ??
After I traded the Yaris 3 door, I later got into a Honda Fit with MT and with VTEC (L15A7 SOHC no cam phasers) and it could care less about oil viscosity. Maybe a slight windage loss with thicker oil but nothing to put it into the category of "this is not running to a target design intent!" Solid engine, no chain noise - just known for toasting coil packs likely due to proximity to the cast in head exhaust runners.
This year it appears to be ACEA C3 0W30 in the Form of Mobil 1 ESP
SilentType
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Well...it seems like 5W-30 isnt the perfect choice for turbo direct injection.
Bearings will starve
I have put 5w-40 in both the Ford 3.5 liter Ecoboost and the GM 5.3 liter V8 without obvious issues. GM even told us its ok to put 0w-40 into their engine and it has cylinder deactivation. When I saw demonstration of how the lifter works I thought for sure 0w-20 was the only choice.
Todays 5w-40 "Euro" sold at Walmart is not as thick as traditional 5w-40. Keep in mind the range of 5w-40 is 13.0 to 16.0 cst@100 degrees Celsius. Looking at 3 popular European oil brands sold at Walmart it appears to be a robust 5w-30 which will ultimately shear down to 5w-30 in most any engine.
Typical European 5w-40 sold at the local Walmart
Mobil 1 13.7@100 degrees C
Valvoline 13.5
Castrol 13.4
Looking around Walmart you have to go to the HDEO aisle to find traditional thickness 5w-40 such as Shell Rotella T6 or Mobil 1 Delvac ESP. Only the Mobil 1 formula has a gas rating of API SN and calling Shell's customer service you learn that Rotella T6 5w-40 is not rated for gas engines. Going online to the Amsoil and Redline websites you find thicker formulas.
I dont see any issue putting in what is basically a stout 5w-30 into most any engine or at least the engines to which I have experience.
Todays 5w-40 "Euro" sold at Walmart is not as thick as traditional 5w-40. Keep in mind the range of 5w-40 is 13.0 to 16.0 cst@100 degrees Celsius. Looking at 3 popular European oil brands sold at Walmart it appears to be a robust 5w-30 which will ultimately shear down to 5w-30 in most any engine.
Typical European 5w-40 sold at the local Walmart
Mobil 1 13.7@100 degrees C
Valvoline 13.5
Castrol 13.4
Looking around Walmart you have to go to the HDEO aisle to find traditional thickness 5w-40 such as Shell Rotella T6 or Mobil 1 Delvac ESP. Only the Mobil 1 formula has a gas rating of API SN and calling Shell's customer service you learn that Rotella T6 5w-40 is not rated for gas engines. Going online to the Amsoil and Redline websites you find thicker formulas.
I dont see any issue putting in what is basically a stout 5w-30 into most any engine or at least the engines to which I have experience.
I’ve always run 0/5W-20 in mine
. Maybe not perfect but if it works, it works.
Hard to believe some of this nonsense, isn't it?
strange , I just checked my fuel records, and fuel consumption is 8% better now I have 10W30 in it, from 0W-20 back then. I also have 75W-90 in the transmission, from 75W then....
Nothing. But for what purpose? 13 and a half yo Ford Focus happily running 20 grade its whole life in my driveway. What would be different running 40 now? If I had run it from day 1?
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4wd
$50 site donor 2026
I know - they did not put the dash in the right place
A few years ago SAE added 8, 12 and 16 grades, but unfortunately no SAE 35. Winter grades were adjusted down 5 degrees C about 20 years ago.2.5W-35. Everyone wins!
Where would SAE 35 dovetail in? Maybe 11.5-13.5@100C, HTHS minimum 3.3?
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