[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.