Oil viscosity numbers, and does "Winter" actually matter?

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Apr 29, 2021
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Oils are confusing. I'm trying to understand if the 0W, 5W, or 10W actually matters if it's never below the rated temps? As I understand it, the W number is purely how the oil flows at cold temps.

Assuming this chart is correct and I'm reading it correctly and it never gets to -30 Celcius, but a person's car calls for a 0W weight, should 10W be fine? Say they live in the desert. -30C is -22F. If it never gets that cold, would they be completely okay with a larger W number?

Conversely, could all cars in colder climates just switch to 0W weight? Say a Toyota 4x4 that is recommended for 5W30, switch to 0W30?

IOW can you go down or up on the W chart at will, depending on your climate?

I don't really understand why the labeling/numbering system was made so confusing b/c it doesn't actually relate to any logical value. The 0, 30, 50, 5, 15, etc. relate to nothing as far as I can tell. If you need to refer to a chart to determine what it is used for, it's simply more complex that it should be. Correct my misunderstanding please...

If I were labeling oils, for instance, SAE 30 would be called SAE -5/+35C. And SAE 5W would be SAE -35/-10C. And SAE 0W30 would instead be labeled -40/+40C. Makes sense, right?

Engine-Oil-Viscosity-Chart.png
 
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I am working on my taxes. Even TurboTax is getting confused over the tax laws! lol


"I don't really understand why the labeling/numbering system was made so confusing"
 

ZeeOSix

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It's not as confusing as some people try to make it. The info in the owner's manual is there for a reason, and people should refer to it especially for the W call-out. Not all vehicle manufacturers have identical oil viscosity vs ambient temperature charts when you start comparing the lowest use temperature for a given xW rating.
 
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Well if you believe "no oil is too thin cold" then it matters. If you don't care about the effects of the detailed physics and if "good enough" is good enough for you, then it doesn't matter.
 
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I've been using conventional 10w40 year around for the past 44 years and my engines outlast the rest of the car. About the coldest we get most winters is maybe negative single digits F but I had 10w40 in my car when temps hit -28F around Christmas of 1990. 5w oils weren't that popular until the '80's and 0w has just become popular in more recent years. If someone wants to run 0w8 that's fine with me it's their car to do with as they please. Personally I don't want something that's going to run like water when the engine gets hot in stop and go traffic.
 
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Well, I look at it this way, unscientific, but fits my thought process. Take a 0w-30 and a 10w-30. Each of these oils are going to have the range of a 30 grade oil at 100*c. But we all know that a 0W will flow at a lower temp than the 10w. So, seems to me, that short of the 100*C viscosity range that both oils will eventually get to, at say, 80*F, the viscosity is very different between the two. The 0W being ”thinner” at that temp than the 10w. If one is curious, go buy a quart of each, and pour each one out at 80*. I’m betting the 0W will empty a bit faster than the 10w. That will also equate to a better CAFE response over the big fleet. Just seems to me people look at the extreme end of either side of the oil. I hear, “it’s a 30 grade so it shouldn’t matter. Well, at 100*C, it is. But at different temps, it’s different between the two. At 0*C, they will still flow different. That’s my thinking on it.
 
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So, just a page of snarky comments?
There was a good reply once, and I'll attempt to be concise. 95% of what you see on BITOG is for mental masturbation. Perhaps 1 out of 10 posts actually has any merit or helpfulness. "What are you listening to right now" or "What are you watching right now" or "What are you doing right now" posts? Pulease. The main reason I check back here is for deals on oil, which this board is good at finding. So, welcome to BITOG!!! 🍺
 
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Well, I look at it this way, unscientific, but fits my thought process. Take a 0w-30 and a 10w-30. Each of these oils are going to have the range of a 30 grade oil at 100*c. But we all know that a 0W will flow at a lower temp than the 10w. So, seems to me, that short of the 100*C viscosity range that both oils will eventually get to, at say, 80*F, the viscosity is very different between the two. The 0W being ”thinner” at that temp than the 10w. If one is curious, go buy a quart of each, and pour each one out at 80*. I’m betting the 0W will empty a bit faster than the 10w. That will also equate to a better CAFE response over the big fleet. Just seems to me people look at the extreme end of either side of the oil. I hear, “it’s a 30 grade so it shouldn’t matter. Well, at 100*C, it is. But at different temps, it’s different between the two. At 0*C, they will still flow different. That’s my thinking on it.
Not necessarily most 10w30 you pull off the shelf is API RC/ILSAC while 0w30 is usually more of a ACEA A3/B4 grade so at room temp on a warm daythe resource conserving 10w30 is actually going to be thinner than a 0w30 A3/B4.
 
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Yes about the cold starting temps , but it is simple, just use the recommended oil in the manual. No this is not a snarky reply but lets keep it simple there is no need to make it harder.
 
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