Quote:
Originally Posted by chris_flies
In Summation:
The first number, found with the W, indicates the relative COLD TEMPERATURE viscosity, measured in freezing conditions. 0W flows fastest cold, 5W is a tad slower, 10W is a thin syrup, 15W is a tasty syrup, etc.
Generally, if you live in a climate that experiences temperatures around or below 20 degF, a 0W oil is gonna be best for you, and will offer the best cold start protection (flows faster, fills those lifters quicker).
If you never or rarely dip below 30 degF, a 5W oil would offer more protection than a 0W, but either works fine.
If you never or rarely dip below 40 degF, 10W is a great choice, offering better protection immediately at start-up, and 15W if you're on the warmer side of things.
The second number, without a W is the relative OPERATING TEMPERATURE viscosity. The higher the number, the better protection this offers at high loads, high temps, etc. However, higher viscosity also means decreased fuel economy, and a greater amount of parasitic (right term?) loses in the engine. -20 offer great economy, but little serious protection; -30 is what nearly every manufacturer recommends now; -40 is on the thicker side of things, and is usually recommended for high performance applications, but reduce fuel economy; -50 offers the greatest protection, but is the most detrimental to economy, and is generally the most expensive.
For this number, it's almost always best (for the engine's longevity, at least) to go with the thickest viscosity you can find. For the economy-minded individual a -30, for the spirited-driving enthusiast a -40, and for the racers among us a -50.
I'm not a total expert, but I do understand the physics, and the basic principle of engine lubrication (more is better). I'm open to answer basic questions, and Engineering Explained has a great video on this, as does Gears and Gasoline on YouTube (fantastic channel, deserves your subscription!).
By the way, I'm running a 0W-40. Cold starts are fine (no lifter tick), and it feels great when warm, and doesn't seem to mind light track work.
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You are correct there, trouble is dealerships will recommend and use only 1 oil weight no matter the climate conditions or your driving style.
I lived in Dubai for 20+ years and they use 5w30 on BMWs, Porsche, VWs and some Ford models.
I do not see that oil surviving 50c summers and lows of 35c during the night. That oil is great in winter over there, where 10c lows and 25c highs.
I remember running a 0w-40 in summer there, when i checked the dipstick after a spirited drive, the oil was as thin as water, oil pressure was at bare minimum (1 bar at idle) and oil temp easily hit well over 130c. Would never run that oil on even track days there either, yet the dealership would not run anything different.
Dealership can run whatever they want "strictly" and most of the time the local conditions are well outside their recommendations, yet when you get a new car you are stuck with what they recommend due to warranty reasons.