0w-40w, 5w-50w, 20w-40w, many different answers from different mechanics, seems like they not even too sure in detail. Front number if 0w=for easy cold starts, then what’s 20w and the Back number 40w to 60w=thickness of oil or max temp range it will peak? Or is it the other way round?? Any clear answers, anyone?
A quick explanation.
The Society of Automotive Engineers developed a number system to grade an oil’s tendency to flow at different temperatures. In single grade oil like SAE 30, the number is a rating for how well the fluid flows at lower temperatures. In multi-grade oils (10W30) the first number refers to the same thing, the oils tendency to flow at colder temperatures, the lower the number, the lower the temperature it will flow easily at. The "W" does not mean "Weight", it stands for Winter. The second number is a rating for how well the oil will flow when heated up to aprox. 100C or 212F.
Now, about your old BMW. You’ll find as many different opinions as people who answer. My PERSONAL opinion is to repair the engine so it does not leak and then use the factory recommended oil grade. If you feel you need a little "something more", then use a bottle of Lucas Oil Treatment.
Good Luck
