Oil viscosity

[taysidedragon]

In the search for better fuel efficiency, engine oil has been getting lower and lower viscosity. I'm now seeing oils getting down to 0w viscosity!  How much protection does that give a modern engine? Is better fuel efficiency at the cost of shorter engine life?
I know we can't (wouldn't)  use thin oils like that in our sohc engines, but I'm curious about the need for such low viscosities.

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[Bryanj]

A lot of modern car engines are designed for it and thicker oil invalidates warrantee

[McCabe-Thiele (Ted)]

With finer machining tolerances I guess a thinner more searching oils is essential.

My understanding is that Synthetic Oils were developed in part in a bid to reduce oil changes/ thus service costs  between engine services especially on large industrial engines such as in Aviation, Shipping etc.

Mobil 1 was used in a BMW to cover 1 million miles without an oil change as well as many other tests by independent oil testing companies such as the likes of Lubrizol etc.

https://www.google.com/search?q=mobil+1+a+million+miles+without+oil+change&rlz=1C1CHBF_en-GBGB934GB935&oq=mobil+1+a+million+miles+without+oil+change&aqs=chrome..69i57j33i160l3.20121j0j15&sourceid=chrome&ie=UTF-8

My understanding was that one of the biggest issues for Synthetic Oil was to reduce some of the acids that would build up over time with a possibility of causing corrosive engine damage. One of the many solutions was the use of  various additives amongst them was   micronised chalk to counter the acidity issues.

[Skoti]

Aye,

some hybrid vehicles use 0w/8, reduces crankshaft drag and lowers emissions etc.

https://motorex.com/en-ch/news/2023-03-23-the-new-low-friction-oil-concept-t-xl-sae-0w8-protects-engines-and-the-environment--390219


My 2022 VW Transporter van uses 0w/30 long life 3 oil, with change intervals at 10,000 miles, older models were on 20,000 intervals.
I'm hearing reports in the trade about VAG vehicles having premature engine failures which are supposedly blamed on previous longer oil change intervals.


My old CB750F1 gets an oil change every 1,500 miles, and I sleep easy.