Why are newer cars using thinner motor oils?

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Well, in the U.S. it is mainly for fuel economy reasons. As there are other countries that have the same vehicles/engines and they require different oils all together. Maybe those countries can't get our thinner oils.
 
It's for efficiency, largely to drive CO2 emissions down. Given that these new engines are getting pretty power-dense, the challenge is to create oils that protect these more highly-strung engines, over longer oil drains, often with smaller oil charges, reduced additive content (for DPF and TWC protection) and lower viscosity.
 
Originally Posted By: Merkava_4
It's for fuel economy at the expense of engine life.


Engine life? Really?? Any data to back that up, I didn't think there was a longevity issue with engines, especially imports.
 
I actually read where Volvo did a wear study to compare the effects of the new thin oils versus 5W-30. I can't remember the exact number, but wear increased around 5%.
 
Originally Posted By: Ducked
In the US?

Driven by fatter people. Diet Coke demographics.


Sounds facetious but is actually somewhat true. Just look at the Toyota Sienna's "evolution." It has gone from a relatively trim looking van at intro years ago, evolved from the Previa, to what we have today which looks a lot like a giant pregnant hamster. I mean, really, how much wider are they going to make it to continue accomodating the increasing physical width of their target demographic?

Pretty soon we'll have to widen traffic lanes to fit the ever increasing girth.
 
Originally Posted By: Kestas
I actually read where Volvo did a wear study to compare the effects of the new thin oils versus 5W-30. I can't remember the exact number, but wear increased around 5%.

+1
It's in congruence with the laws of physics in thinner MOFT from thinner oils -> lubrication regimes shifting from right to left (in stribeck curve) -> potential increase in adhesion and abrasion wear ......
which are somehow mitigated by modern AW/EP additive package ...involving billions of R&D costs.
Besides corrosion wear constitutes more significant proportion in engine wear, not so much in gear train wear though.
We now have new normal in acceptable wear from Honda according to quotes from Shannow.
The study of lubrication/tribology fundamentals used to be based on minimum or zero wear.
 
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Originally Posted By: Kestas
I actually read where Volvo did a wear study to compare the effects of the new thin oils versus 5W-30. I can't remember the exact number, but wear increased around 5%.


And when they (Volvo) specced a 0W20, they made the HTHS minimum 2.75 rather than 2.6
 
It is completely about the CAFE regs. Car companies in the US must specify the oil that was used to get their CAFE fuel economy ratings as the spec, and only oil. This is why the same cars in the rest of the world provide a long list of acceptable viscosity, but only the thinnest is spec'd for the US and Canada.
 
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I occasionally use Blackstone labs, but most often use Aviation labs (avlabs) for my wear metals check. These guys have the data, and occasionally publish something interesting.

As always, wear rates by brand of oil does not seem to vary much. Wear rates by type of oil is similarly inconclusive. However, one thing does tend to stand out, viscosity. With some engines, a higher than recommended viscosity can result in significantly lower wear rates.

My V8 and Ecoboost Ford trucks all experience significantly lower wear metals on a higher viscosity. In particular, Mobil 1 EP 10W-30 and especially M1, 5W-40 TDT reduce the wear rate per mile vs 5W-20 or 5W-30. Same goes for my Turbo S2000. Wear rates decrease significantly with M1, 15W-50. But at almost 450HP (crankshaft) 407RWHP, and no oil cooler, a robust oil is required.

And again, many engines with timing and/or balancer chains do far better with higher viscosity. Ask the GM warranty department about all the premature balancer chain failures.
 
Originally Posted By: Ducked
In the US?

Driven by fatter people. Diet Coke demographics.
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Originally Posted By: AdrienneOwens
Many Thanks
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Despite the limitations of the search function on this site I think it is still possible to find many, many existing threads on this subject.

You joined just to ask this question? Have we seen you before under a different screen name? The grin emoji kind of makes me think we have.
 
There are countless hundreds of thousands(perhaps millions) of engines in the US using 20 wt oils with very high mileage. No epidemic of failed engines. I chose to use 0-20 oils in my Fords, and have for several years, because of the benefits it provides. Very clean engines, have never had an engine using 0-20 show signs of wear, great cold engine starts(about 80% of engine wear occurs at start), outstanding protection in extreme cold and hot temps, a bump up in MPG, no sluggish feeling like with heaver oils, quick oil flow to the cam area in extreme cold starts, and zero oil use in my normal 10K OCI. I have put around 400K on engines using M1 0-20, so my experience is not with a couple of OCIs.

However this thread should be under the gas engine section, and welcome to BITOG and prepare to be confused.
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My 2017 VW Alltrack with the turbo 1.8 liter uses 5W-40. So a German take in oil for the car. Yet it gives in the high 30,s for mpg on a trip.
 
Bravo Cujet, a well written bit of information. Thinner oil's do not cause "acute" damage, but long term "chronic" wear is higher verses using a heaver weight oil. Avlabs is a "no [censored]" business that shoots straight.
 
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