@haseeb.basharat
Sir, latest generation PKDM Altis 1.6 has 1ZR-FE engine, and is the same found everywhere in the world (please correct me, if this engine has different design criteria and specs for Pakistan).
As per http://mywikimotors.com/toyota-1zr/ , recommended oil grades are 0w-20, 5w-20, 5w-30 and max. 10w-30, and as per http://oil4motor.com/en/cars-oil/TOYOTA/Corolla-1.6-Dual-VVTi-(1ZR-FE---91kW)-(P-(Petrol))-(2007-)/33196 and http://oil4motor.com/en/cars-oil/TOYOTA/Corolla-1.6-(1ZR-FE---91kW)-(P-(Petrol))-(2006-2007)/33192 , again, the recommended oil grade is 5w-30. I could not find 5w-50 anywhere, even on a single website, where it has been recommended for 1ZR-FE.
Even in the manual (copy of the page from manual is mentioned in a post above), the oil grades are 5w-30, 10w-30, 15w-40 and 20w-50. I can not believe that they have even mentioned API SL and SM grades! Who would use API SM or SL grade engine oil in a brand new 1ZR-FE engine, which is based on latest tech.? I can just pray for the sanity of manual preparation team!
Would you ever pour an oil grade with API rating of SM or SL in your ride? I believe NOT! Ever! and then 20w-50? (Although they both are mentioned in the manual)
{Now even API SN Plus rating is available, which is even more better as compared to API SN. Why not move towards it, and come at par with the rest of the world? And I can swear that the engine, which has been perfectly designed and tested on API SN oil, would for sure work even more better in API SN Plus engine oil.}
They have mentioned oils from 5w-30 API SN to 20w-50 API SL. What to say now?
Then ILSAC has been mentioned, but not specific (like GF-4, 5, etc.). GF-5 is currently in use, with working on GF-6A and 6B in progress.
Now let's come to Toyota Taglon. Here is what's mentioned on the website ( http://www.toyota-indus.com/after-sales/parts/lubricants/ ):
Taglon
Taglon Gasoline Engine oil is high performance Synthetic engine oil formulated & imported from Japan with good quality base oil which meets the demand of petrol engine especially in lower temperature condition. (what about high temperatures here?)
General Characteristics
Meet API service category SN/CF & SAE 5W-50
Meet ILSAC GF-3 standard.
Designed to use in Gasoline / Diesel Engine
Design for smoother engine protection in low temperature condition of modern engine
Longer engine life.
Excellent startup protection
Maintain an oil film even in the low temperature up to -40Ā°C (again, what about high temperatures here?)
Excellent control on oxidation, corrosion, wear & oil consumption
More than 5000 KM mileage
Imported from Toyota Motor corporation Japan
Now let's analyse its parameters:
Its service category has been mentioned as API SN / CF. CF is Diesel C Category, and is obsolete as per https://www.api.org/products-and-services/engine-oil/eolcs-categories-and-classifications/oil-categories#tab-diesel-c-categories
Coming towards ILSAC GF-3. GF-3 is also obolete as per https://www.api.org/products-and-services/engine-oil/eolcs-categories-and-classifications/oil-categories#tab-ilsac
Now should Toyota Taglon 5w-50 be used in any brand new Toyota car, and brand new engine based on latest tech.? I would give a big NO to this outdated oil, based on obsolete parameters, for engines based on new tech. Only engine oil grade / viscosity does not matter, other parameters also need to be considered to take the best out of any engine.
Even if keeping the oil grade same, at least they should make ILSAC rating and API CF rating, better, best & current! 
Guys, Toyota Taglon 5w-50 is outdated and obsolete as per latest ILSAC and API Diesel C Category. Exercise caution in its use.
Sir I will not agree to it. Engine thermodynamics will always remain the same, in Pakistan, or USA; in winters or in summers.
I was just going through the owners manual for Corolla USA model, and was surprised to know that currently 0w-20 has been recommended. Can you believe it? Manual source: https://www.toyota.com/t3Portal/document/om-s/OM02509U/pdf/OM02509U.pdf page 541 / 608. Then latest ILSAC GF-5 has been recommended, why GF-3 here?
If we have bad fuel, do we also deserve obsolete API ratings regarding Diesel C Category and ILSAC?
If we have extreme heat in summers, then some regions in USA are also extremely hot, like Arizona, Death Valley, still, 0w-20 has been mentioned for throughout use in USA (and same had been for Honda).
Even Atlas Honda now is pouring 0w-20 in all of there brand new cars.
Regarding fuel quality, I do not think fuel makes any direct contact with engine oil (unless / until the rings, pistons, etc. are deteriorated, and engine oil gets burned with fuel in combustion chamber, but in that case, what wil oil do? Or what can oil do?)
Then regarding dirt, in that case, air filter takes the toll, and not the engine oil. Just keep the air filter clean, and you are good to go. However, if you are using bad / choked air filter, then engine oil can not do anything. Engine will have to exert more efforts in case of clogged air filter, so more heat stresses, and coupled with thick engine oil, well... engine may start crying!
Even in USA, some regions have very dusty environments but still, 0w-20 has been recommended.
Yes, this makes sense to me, since Fuel Filter and Fuel pump has direct contact with fuel, and if its of bad quality, then definitely, filter will choke, but still, nothing to do with engine oil.
Sir, if your friends are using Mobil 5w-50 and their cars are fine, then its a good thing, no doubt! But still, we all should follow what OEM suggests, and if OEM like Toyota Indus makes some mistakes in their owners / users manual and pours / recommends Toyota Taglon 5w-50 in their vehicles (based on obsolete API CF and ILSAC GF-3 criteria), then we should make the correction by some logical working, and choose the best thing for our ride, wisely.
I think, I should stop now (enough debate and discussion).
