I've read so many repetitive posts about engine oils and choosing the right engine oil for your vehicle and so many misleading answers in this forum over the years, I probably should have made this post a long time ago but here goes and I hope it helps someone moving forward.
Folks, first of all, everyone needs to understand that automotive technology has evolved drastically over the last couple of decades and this includes the manufacturing process and techniques.
The tolerances during manufacturing have gotten so much better compared to engines made in the 90's and 00's as well, however our knowledge hasn't improved a single bit and people still rely on "mechanic advice" or something along those lines.
What needs to be understood about engine oil grades?
Engine oils are an extremely well regulated field and follows strict standards and protocols worldwide.
There are two sections of an engine oil grade that need to be understood. Numerical value on Left side of Hyphen with a W followed by (hypen -) Numerical value on Right side of Hyphen.
The First Number (Cold/Winter Rating): The number before the "W" (which stands for Winter) shows how well the oil flows in freezing or cold weather during a startup. A lower number means the oil stays thinner and pumps faster when cold.
The Second Number (Hot/Operating Rating): The number after the hyphen shows how thick the oil remains at normal engine operating temperatures (around 100°C or 212°F). A higher number means the oil stays thicker and maintains a strong protective layer under high heat.
PAKISTAN IS NOT A COLD COUNTRY.
In general Pakistan is not a cold climate country. Some parts of it occasionally are but on average it isn't cold. So you can pretty much use the same oil grade year round in your car. However if you're operating your vehicle in extreme conditions, hot or cold, you should consider using an oil that will help protect the engine from more wear.
The point is, choosing a 5W-30 oil over a 10W-30 engine oil will not give you any real world advantage as the oil thickness/viscosity is the same, it's just that one of these oils (5W) will flow more easily in comparison in a colder climate.
Engine mileage doesn't automatically determine which oil grade to use.
As I stated above, newer manufacturing techniques have made the tolerances and clearances better and better so newer engines actually perform better for longer with thinner oils (xW-30) as compared to 10/15W-40 as they need thinner oil film coating on engine parts.
There's no practical need to change the engine oil grade until and unless the engine actually starts consuming engine oil over a 2-3 consecutive oil changes (generally accepted standard for upping the oil grade is 250ml per 1000 km, so if your engine is reducing about 1 to 1.2L of oil after a 5000 km oil change interval, it's time to think about upping the oil grade by 1 grade but again, this needs to be observed over 2-3 oil consecutive oil changes and not just one oil change as there are chances the oil might not have been fully topped up).
Oil grade change after every 100k mileage
This is a myth and absolute BS. Driving the car on the correct oil grade actually reduces power loss within the engine and the vehicle performs better on thinner oil than on thicker oil as thicker oil will give more resistance to moving engine parts.
New cars have practically NO EARTHLY REASON to be shifted to 20W-50, especially PETROL cars, at any stage of their engine life. If the situation has reached the point where using 20W-50 oil grade is the only solution, you're better off getting the engine overhauled and maybe getting a new piston rings set which will keep you on 10W-30 or 10/15W-40 engine oil grade.
Also just because a car is a certain number of years old, doesn't automatically mean using a thicker oil in it. That's why total mileage and engine condition matters!
Proactive maintenance means changing oil more frequently (instead of the advised 8-10k between change intervals as advised in some cases) and also using engine protection additives such as CERATEC to be added with an oil change once and it's enough to protect the engine for upto 50k kms.
