Agreed. But what if the engine has very tight clearances? And thick oil may not be suitable (like parameters of 5w-50, are almost double than 5w-30, and even 10w-30).
For extreme driving conditions (like towing, driving at extremely fast speeds for continuous, non-stop time and considerable time), of course thick oils can be recommended by the manufacturer, but for normal, usual driving conditions and for city use, 0w-20, 5w-20, and at max. 5w-30, serve the purpose very well IMO.
For me, its a bit difficult to "digest" that 5w-40 does not suit, but 5w-50 suits 1KR-FE?
Agreed, and I think that small 660 cc and 1000 cc engines (in locally assembled PKDM cars, and JDM cars) are designed and meant for fuel efficiency. Accordingly, they need to be feeded with thin, but recommended oil grades.
Sir, similar conditions are faced by vehicles in some of the states in even USA; the weather / temperature becomes extremely high in summers, combined with humidity, AC is also always used, sometimes, there is stop-and-go traffic, and even at some places fuel is also of bad quality, still, almost all the new vehicles / models are being feeded with 0w-20 (or may be even 0w-16 in some cases).
Let's leave USA, and talk about Pakistan. Even Atlas Honda is now pouring 0w-20 in brand new Civics, Citys, and BRVs (although City is a decade old model, and previously 5w-30 was feeded in it, but now, they have shifted to 0w-20 for Honda City. Source: https://www.honda.com.pk/parts/index.php/products/bycategory/6 ). Following is written as of now:
Motor Oil, Engine Lubricant
Other Name : HONDA ENGINE OIL (3.7L) SN 0W20
Models: Civic 2016~ , City 2017~ , BR-V 2017~
Part Number : 08234P99A8NB1
I personally believe that if 0w-20, 5w-20 and 5w-30 are mentioned in the owners / users manuals of cars, and also recommended by the OEMs, then for sure, they can work absolutely fine in that car, under normal working conditions (provided oil is from reputed brand, and good quality, which can easily bear high engine temperatures, and do not thin out and deteriorate quite early).
Rest, all have personal experiences which cannot be challenged, but by-book, I think above mentioned text is correct.
