Learning a lot at school but this was another ah ha! moment oil when reading i.e. 5w30 most people think the w stands for weight.

What the numbers mean

The numbers and letters on a container of multi-grade motor oil will tell you at a glance what its operating range is and how it compares to other oils. Here’s an example:


5: This is the oil’s viscosity rating at low or winter temperatures

W: This stands for “winter,” and is part of the “5” rating

20: This is the oil’s viscosity rating at high temperatures

What this means is that the oil industry scientists, in their labs, have created lubricants that flow better at low temperatures than they do at high temperatures. This is exactly what your engine needs. You get easy cold starting, combined with excellent high-temperature protection.

I bet if you called down to oriellys and asked for some 5winter30 they would go huh?lol.

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Close but not quite. The first number describes the behavior when cold. The second number describes its behavior when warmed up to 210F. This is because a single weight oil will get thinner (less viscosity) as it warms up. So a straight weight SAE5 might have the viscosity of water at higher temps. For anybody who doesn’t know viscosity describes a fluid’s resistance to flow, so a more viscous fluid is thicker.

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your right sorry for confusion will edit however it would get thicker at higher temp right ?

i know that sounds backwards but you gotta love chemistry

Not quite.

This is an over-simplification, and not 100% accurate, but it’s a good analogy for understanding multi-viscosity lubricants.

Think of an old 2-speed powerglide transmission (or really any transmission if we imagine it has two gears.) You start out in first (low) gear and floor it. As the car picks up speed, the engine revs higher and higher. At some point, you think dang, this thing is gonna blow! So you shift into second (high) gear and the engine lives another day. The two speeds let the engine stay in an acceptable rpm range.

In a similar way, you can think of multi-viscosity lubricants as 2 lubricants in one. At cold temperatures, the lower viscosity fluid does its thing, keeping metal from direct contact with other metal. But as the engine warms up, the lower viscosity becomes too thin and cannot do its job. So, the thicker, more viscous fluid takes over and starts to do the lubricating and does so through the rest of the upper temperatures. When the temperature comes back down and the fluids start to become thicker, the higher viscosity is too thick and the lower viscosity fluid takes back over.

I don’t know of any lubricants that become thicker as the temperature goes up, but what I think you meant is that the higher viscosity comes into effect at higher temperatures.

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Honestly your explanation makes more sense i was having a hard time wrapping my head around how a fluid could get thicker as it got hotter, physics dont work like that to the best of my knowledge! Thx for taking the time to set me strait!

Also with all this talk about fluid and temperature check your car fluids in this weather is a good thing to do.


Not me. If I did that, I’d have to worry about my personal fluids all freezing solid. My Explorer is just going to have to deal with it.

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Oils are a complex formulation with many additives. The component that “kicks in” at the higher temperatures is called a “viscosity index improver” or VI additive. It is actually a polymer and it stays in solution under all temperature conditions. The VI additive has a very high molecular weight and some of them actually change shape with temperature changes, i.e. “curl up” at cold temperatures to keep the oil thin and then “fold out” at higher temperatures to help thicken the oil.

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To be more precise, the VI additive(s) don’t actually make the oil “thicker” at higher temperatures, they just cause the oil to get less thin. Hope this helps.