Yup. You are Right. I won't recommend ZIC.
I had used http://zicoil.pk/product/zic-x9-5w-40-vhvi-tech/ but repented. It was the best oil in its range by ZIC, fully synthetic and the most pricier. But it couldn't even bear beating of ~4000kms, volume of the engine oil reduced and at the time of oil change, it was just like as if water is coming out of the engine, got too thin. So ZIC is not recommended at all, at least which is available in the local market.
I now use http://www.eneos.pk/sustina-5w30-snrc/ and fully satisfied with it. It costs Rs. 4500 for 4L packaging with change interval of ~8000kms or more. Last time, I changed it at ~8500kms and I was amazed that it's volume had not been reduced and viscosity had also not been deteriorated much. Since your vehicle is more than 200,000kms on the odometer, so, 5w30 is not at all recommended for your vehicle.
Coming towards your queries, I will answer to them based on my learning and knowledge:
Bro, first of all, switch to SN API rating ASAP.
Considering that you own GLI, 2010 model (08 years old, and falling in the category 05-13 years as per shell oil guide), I would personally suggest 10W-40 oil grade. I do not think there will be any issue if you switch to 10w-40 from 20w-50, in fact engine over-all performance and fuel efficiency will improve.
I would not suggest 15w-xx or 20w-xx, they will be quite thick.
In 10w-40, please have a look at http://www.eneos.pk/eneos-10w40-sncf/ or http://mobilpakistan.com/mobil1.php?mid=3 or https://www.shell.com.pk/motorists/oils-lubricants/helix-for-cars/shell-helix-mineral-motor-oils/shell-helix-hx5-sl-cf-a2-b2-10w-40.html (Please note here that in the description, API SL has been written, but on the yellow Can, API SN has been written. As long as SN is there, the oil is good to go).
Note: The links are for reference only and to guide you / give you idea regarding the specs. Please buy from the store you trust.
Eneos 10w-40 aapko Attock k petrol pump sey milay ga. If thinking of this one, then try to buy it from that Attock petrol pump, which is company maintained. You can get details regarding company maintained petrol pumps from the internet or their website.
And do not worry about temperature of your city. Since your engine is water cooled (and I am assuming that you are using a good quality and excellent coolant) then do not worry about outside temperature, whether it drops to 5 degrees or rises as high as 47 degrees, no need to worry about oil viscosity.
For oil change interval, you should consult from the dealer from where you buy the oil or OEM recommendations.
Also keep on checking oil volume and viscosity after regular intervals. Good quality, genuine engine oil may lose some viscosity after taking beating, but will not reduce its volume considerably.
Engine 02 cheezain hi maangta hai:
1. Genuine Engine Oil with its drain / change after regular intervals
2. Radiator / Cooling system working in perfect condition
(Ye 02 cheezain milti rahein, engine kahein nai jata!)
Do not use any sort of oil additives with engine oils. I won't recommend them, and usually, all oils now a days come with additives blended in them.
For ultimate oil guide, you may have a look at: https://www.carbibles.com/guide-to-engine-oil/
I hope, above detailed explanation solves your concerns.
Jazak ALLAH and thank you.
