Oil Weight theories/conspiracies?

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Absolute
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5:29p, 5/20/26
AG
Recently googled the recommended oil weights of a couple new to me vehicles. Both came back as 0w-20, which is a little weird since they are very different engines - 2023 Buick Envision turbo 4 banger Daughter's car and 2022 GX 460 NA V8.

So now my very limited social media time is bombarded by stuff about 0w-20 being bad. I am old enough and mechanical enough that I do wonder about it. Particularly in the Texas heat. I understand that manufacturer specs are not necessarily always about optimization and sometime profit and CAFE standards influence specs. Anyone remember the stupid blocking gate on 2nd and 3rd gear on 90's camaro shifters?

Figured I would come to the Aggie auto experts like 1ags and see what you guys think. All smoke and mirrors or is there something to it. I did ask AI and it was kind of humorous the way it tried to justify things. Also that it told me the GX has a 6 cylinder and argued about it twice with me before relenting that I was correct that it is a v8.

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1agswitchin4lanes
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7:12p, 5/20/26
AG
I'm using 0w40 or 5w40 in all my personal vehicles regardless of recommendation.

My fleet customers all get 5w30 unless they specify otherwise.

Ford transit with same engines have 5w20 and 5w30 recommended weights within one model year with no mechanical difference.

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Absolute
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In reply to 1agswitchin4lanes • 8:32p, 5/20/26
AG
Do you believe there is a wear and tear / performance / longevity benefit or reduction in the choices one way or another?

That was the funny AI question. About different specs for the same engines around the world. It did not have a good explanation for the difference and fell back to different gas mixtures and national requirements. Since gas and oil should not mix, that is stupid.


End of the day, just want my vehicles to be protected and perform and last. Not looking to make any type of statement.
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fixer
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6:14a, 5/21/26
There is alot of clickbait grift and AI generated drivel being made for clicks on this subject.

Unless you have XLRotor or Dyrobes program on your home laptop, back checking the OEM recommendations on oil type can be difficult but not impossible.

TLDR: Be suspicous of 0W20 and long drain intervals. It can work if the bearings, cooling system, and powertrain mapping are designed for it.

If an engine used a specific grade of oil for a long time and suddenly the OEM switched to a lower visocsity, then suspicion is warranted that the change was driven by reliability and durability reasons. Double the suspicion if the engine power increased or the final gear ratios have decreased.

The derivative of this is if the OEM specifies a different oil weight for the same engine in a different car (application) or a different region of the world, then suspicion is warranted.

In the case of the GX, Toyota has used 0w-20 forever on many engine platforms.

On my 2019 Tundra I switch to 5w30 in warmer months.

Toyota manuals typically have a section on oil type that essentially indicates when you should up your viscosity based on operating condition.

GM manuals haven't done this for a good while now.

Huge power outputs per specific engine displacement aka power per liter. If the engine is well north of 100 hp per liter then suspicion is warranted with 0w20. The rod bearings in this specific power output are heavily loaded.

To use lower and lower oil viscosities with very high power per liter, the engine oil cooling system has to be robust to keep oil cool enough to maintain the right viscosity range; the gear selection and programming has to keep engine rpm and load away from a low rpm and high load lugging condition; and lastly the bearings have to be designed for it in terms of materials and dimensions. Small changes in bearing dimensions can greatly influence the load on the bearings and hence the viscosity.

You can get alot of this information with a OBDii plug in data logger.

If you see oil temps consistently above 212F (where the higher number in multi grade oils are rated for viscosity) then you are absolutely operating with lower oil viscosity as oil drops viscosity quickly with added heat. If the engine cruises at 70% or more of full torque and engine rpn is below 1500 rpm it is close to a lugging situation.

Longer drain intervals can create conditions where the oil has sheared down to a lower viscosity range.

This is the main issue with 0w20. The larger the numerical gap between the lower viscosity number and the higher viscosity number the more the oil will shear down to a lower grade. This is because oils are formulated with polymer and other viscosity improvers that mechanically breakdown. To get a larger span of viscosity the more VI is added.

But even 0W20 will shear out of grade and it is starting out at a lower viscosity so it can shear down to a lower "final" viscosity with use.

So long drain itnervals with 0W20 are asking for problems.

Edit…

If there is a conspiracy it is the oems trying to target the minimum on the stribeck curve… and it ain't working out too well.

https://www.fuchs.com/us/en/what-is-the-stribeck-curve/
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Silvy
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7:03a, 5/21/26
AG
Valvoline VR1 10w-30
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Charismatic Megafauna
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8:03a, 5/21/26
AG
If there ever was a case against ai this is it. Unless you specifically ask it to, it's not regurgitating the result of objective empirical studies, it's taking a weighted average of all the garbage that mouth breathers have posted on the Internet (of which there is a lot) and presents it as fact
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fixer
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In reply to Charismatic Megafauna • 8:12a, 5/21/26
Charismatic Megafauna said:
If there ever was a case against ai this is it. Unless you specifically ask it to, it's not regurgitating the result of objective empirical studies, it's taking a weighted average of all the garbage that mouth breathers have posted on the Internet (of which there is a lot) and presents it as fact


This 1000%
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fixer
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8:51a, 5/21/26
Forgot to mention that gimmicks like auto start stop (ASS) guarantees your engine bearings are operating in mixed lubrication regime of stribeck curve much more often.

In other words regardless of viscosity a gimmick like this makes the engine have many many more start cycles that put the bearings out of hydrodynamic film region.
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1agswitchin4lanes
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In reply to Absolute • 10:31a, 5/21/26
AG
Absolute said:
Do you believe there is a wear and tear / performance / longevity benefit or reduction in the choices one way or another?

That was the funny AI question. About different specs for the same engines around the world. It did not have a good explanation for the difference and fell back to different gas mixtures and national requirements. Since gas and oil should not mix, that is stupid.


End of the day, just want my vehicles to be protected and perform and last. Not looking to make any type of statement.



I believe that helps with fuel dilution issue on top of engine protection.

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Trinity Ag
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In reply to fixer • 10:46a, 5/21/26
S
fixer said:
Forgot to mention that gimmicks like auto start stop (ASS) guarantees your engine bearings are operating in mixed lubrication regime of stribeck curve much more often.

In other words regardless of viscosity a gimmick like this makes the engine have many many more start cycles that put the bearings out of hydrodynamic film region.


From a lubrication standpoint, I don't see the this being a big issue on a warm engine. The "stop/start cycle" when the engine management is running rich on a cold start thus diluting the engine with fuel is what affects wear on engines that are sensitive to things like bore scoring.

Im dubious a thirty second stop/start on an engine at full operating temperature is going to reduce bearing and cylinder lubrication in any significant way.

Maybe, but I'd want to see data on it.

Wear on batteries and starters seems like a more likely (though less expensive) concern.



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Trinity Ag
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10:53a, 5/21/26
S
Pretty much every knowledgable Porsche mechanic is recommending high moly 5w-40 in water cooled engines, and 5w-50 in tracked cars due to shearing down viscosity at high track condition temps - higher weights than manufacturer recommended, and about half of the change interval mileage.

0w-40 is only recommended during winter in cold weather climates.

0w-20 seems completely designed to meet arbitrary EPA standards while providing enough lubrication to get through a warranty period without trashing engines.
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austinag1997
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10:53a, 5/21/26
AG
I will take a shot here. I believe the recommended oil may have someting to do with engine tolerances. I mean back in the day, 10W40 was a common oil viscocity. I see a lot more 0W oils these days and believe it may be due to tighter engine tolerances.

That being said.... everyone on this board will provide 20 different opinions about engine oil!
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austinag1997
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In reply to Trinity Ag • 10:57a, 5/21/26
AG
Trinity Ag said:
Pretty much every knowledgable Porsche mechanic is recommending high moly 5w-40 in water cooled engines, and 5w-50 in tracked cars due to shearing down viscosity at high track condition temps - higher weights than manufacturer recommended, and about half of the change interval mileage.

0w-40 is only recommended during winter in cold weather climates.

0w-20 seems completely designed to meet arbitrary EPA standards while providing enough lubrication to get through a warranty period without trashing engines.


I am 0W in 2 of my Porsches. Damn Porsche circulars. Headed to a Porsche dealership for service for the 1st time in my life. We will see how many organs I have to sell.
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fixer
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In reply to Trinity Ag • 11:34a, 5/21/26
Trinity Ag said:
fixer said:
Forgot to mention that gimmicks like auto start stop (ASS) guarantees your engine bearings are operating in mixed lubrication regime of stribeck curve much more often.

In other words regardless of viscosity a gimmick like this makes the engine have many many more start cycles that put the bearings out of hydrodynamic film region.


From a lubrication standpoint, I don't see the this being a big issue on a warm engine. The "stop/start cycle" when the engine management is running rich on a cold start thus diluting the engine with fuel is what affects wear on engines that are sensitive to things like bore scoring.

Im dubious a thirty second stop/start on an engine at full operating temperature is going to reduce bearing and cylinder lubrication in any significant way.

Maybe, but I'd want to see data on it.

Wear on batteries and starters seems like a more likely (though less expensive) concern.


The asperity contact in mixed lubrication occurs at a higher frequency than if the engine stays running.

This will not self delete bearings in 10,000 or 20,000 miles but will wear the bearings much more than most would want over a 100,000 to 150,000 range.
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BrazosDog02
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12:05p, 5/21/26
AG
I don't think the oil thing is as big a thing as the internet wants to make it. Put in what the manual calls for or that makes you feel warm and fuzzy. It will all maintain your motor well passed your expected lifetime of the vehicle.

As I've stated multiple times, my 20 year old 5.4 with 450,000 miles has had oils and brands from 5w20 to 10w40, and even a few straight weight changes. I've not had a component failure in the motor outside of HLA but those usually don't live past 200k….mine died to the point of being noisy at 450k.

I have 6 other trucks from diesels to gas, 20 years old to 1 year old. All of my 6.7's, 6.0, and 7.3 get synthetic 5w40 Rotella T6. All of my gas trucks, from 5.4, 5.8 and 7.3 godzilla get 5w30 Mobil 1. I don't think about it any further than that other than Motorcraft filters always.
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Southside AG
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12:42p, 5/21/26
AG
Oil change frequency is more important because of the oil shearing down out of viscosity range over long drain interval cycles. You can increase viscosity as mentioned if you're worried about fuel dilution over a long drain interval. I use 0w-20 in my bmw and change the oil every 5k myself and the dealer does the free change over other one. The last time the dealer did it, they used 0w-30 instead of the 0w-20 probably because of low stock so that tells me it's fine to move up In viscosity for me. I have a 2024 bmw x4 m40i.
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P.H. Dexippus
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1:16p, 5/21/26
AG
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agracer
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In reply to Absolute • 3:41p, 5/21/26
AG
The Hemi Ram v8 has stated 5w30 for a long time and a few years ago suddenly switched to 5w20. But if you read the manual it says that when not available, 5w30 is acceptable but switch back to 5w20 at the next oil change.
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MouthBQ98
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8:02a, 5/22/26
AG
Yes, manufacturers have been using tighter operational tolerances with oil viscosity in their designs to tease out a few more fractional mPG in testing. If they design the affected wear components properly they can probably get away with this in routine operating conditions. In more normal day to day driving conditions, a more conservative slightly higher viscosity oil might offer better wear protection by keeping a better layer in place on the bearings and such in higher load and temp conditions. I suspect that more frequent oil changes ov the lower viscosity recommended oil would help as it does break down to lower viscosity molecules with use, or going to a slightly higher viscosity range. There are a lot of variables at play so it is easy to see how test case wear can deviate considerably from some real world operating conditions.

I always go with the OEM oil and use good quality stuff and change it in recommended intervals but our vehicles get a lot of ideal warm highway driving time and not nearly as many cold short trip suburban driving use which is what I think wears out engines faster even if properly maintained.
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austinag1997
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7:37a, 5/23/26
AG
."...many cold short trip suburban driving use which is what I think wears out engines faster even if properly maintained."

Yup. That probably exacerbated the Vario camshaft deviations in my 2002 Boxster.
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1agswitchin4lanes
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In reply to austinag1997 • 9:03a, 5/23/26
AG
austinag1997 said:
."...many cold short trip suburban driving use which is what I think wears out engines faster even if properly maintained."

Yup. That probably exacerbated the Vario camshaft deviations in my 2002 Boxster.


The more you drive and drive hard, the better it is.
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87IE
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In reply to austinag1997 • 2:45p, 5/23/26
AG
austinag1997 said:
I will take a shot here. I believe the recommended oil may have someting to do with engine tolerances. I mean back in the day, 10W40 was a common oil viscocity. I see a lot more 0W oils these days and believe it may be due to tighter engine tolerances.

That being said.... everyone on this board will provide 20 different opinions about engine oil!

I'm 17 opinions on the low side
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