All those who are suggesting different brands and grade may or may not have tested it personally but I own a gli 2010 model where I am the first owner of the car and it has been maintained by the 3s dealership throughout. As you know that 3s dealerships pour 20w50 in these cars right from the first oil change at 5000km and same was the case with me where after every 5000 km 20w50 petron was used by the dealership along with genuine oil filter. I call this my era of ignorance or zamana jahiliat in context of oil and oil viscosity. I was a firm believer that the manufacturer know their product best and 3s would always suggest the best but little did I know that 3s in Pakistan is not actually following the manufacturer when it comes to the engine oil.
It was catch22 situation and at this moment my savior was no one but our very own @Xulfiqar because the car was having about 80 to 90 K running on 20w50 and there is a popular belief that once the car get used to thick oil there is no going back to the oem recommended viscosity or thinner oil. The 3S foremen scared me alot that the engine will start consuming oil and seals will leak but Xulfiqar asked me that "its never too late to revert back to the oem recommended oil grade".. I was then told to switch gradually by first switching to 10w40 and then 10w30 and then 5w30 but I did a tawakal to switch directly to 5w30 directly from 20w50. It was very stressed time for me becaue I was scared to death for this swtich but thanks to Allah it turned out very well. It felt like a trailer was towed with the car earlier which has been detached. The car felt so agile and quick ma sha Allah and the fuel ecomy jumped by 2 to 3 km per litre in local and about 4 to 5 km per litre in long and now the car has clocked 139k and I am still using 5w30. First I was using 5w30 total from drum and then when havoline introduced 5w30 then I switched to havoline. I am still using orig filter.
I was changing the oil on 5k and the car is used on motorways only and very less in local. Xulfiqar again guided me that for fully synthetic oil 5k km is waste of money. He guided me to change it at 12k with orig filter but only last month I strectched it to 8k Km as there was ac idling involved due to summer and belive me oil was still good so in sha Allah this time I am planning to strectch it till 10k kms.
Hope this helps.
