Originally Posted By: Nick1994
Now this may be a dumb question, but it's something that has always made me wonder. I get it that the colder environment you're in, the better the idea it is to go down a grade of oil (as in the xW weight). But according to the BITOG Motor Oil University, it says that all oils are too thick at start up, regardless of weight, that the lower the xW of oil you can go, the better.
Not dumb at all. On a cold start it is true, ALL oils are thicker than what the vehicle was designed for. To pick an arbitrary number and vehicle, at 100C(212F) as an oil operating temp, the vehicle was designed to have a 30 weight. When the oil is cold, it is much thicker than a 30 weight would be at the operating temperature.
So when a 10w30 is used, it is thinner at the cold temp than the straight 30. 5w30 is thinner at lower temperatures than the 10w30, and 0w30 even more so. So the lower you go on the "first number", the better the oil flows at a lower temperature even though all four oils are the same consistency at operating temperature.
Originally Posted By: Nick1994
Or that's how at least I interpret it. So using this logic, what's the point of using a, for example, 10w30 oil these days? Wouldn't this logic mean a 5w30 is better on startup, and a 0w20 is more beneficial than a 5w20?Even in a hot environment.
If you live in a warm climate (Florida?) where the temps rarely if ever get to freezing, then a 10w30 is fine. I don't have the chemistry background to discuss in detail, but do understand the concept - that in general, the smaller the spread between the numbers the less chemicals are involved to make the oil adjust to both cold and hot temps, and the better the oil will hold up over time. (that said, the difference in durability between 10w30 and 5w30 used to be huge in this respect, but has narrowed a lot since the 90s and may be gone entirely)
But if you live in a climate that sees subfreezing temps or even below 0F, then it is best to use a 0wxx or 5wxx appropriate for the climate. A vehicle might very well be able to start at -20F on 10w30, but there will be a lot of parts that are starved of lubrication in the time it takes for the very thick fluid to make it around the engine.