Somebody tell me if this sounds correct

[LouDawg]

(Referring to oil weights and oil viscosity...feel free to correct me on anything that's off base)

"The second number in a multigrade oil means that oil will not THIN more than that weight at operating temperature (i.e. 100 C). It does NOT mean that it's thicker at operating temperature than the first number. It's really quite simple. Did you even see the cSt ratings for the PP at temperatures? The polymers coil up so that it will flow better at low temperature. But they lengthen to keep it from *thinning too much at higher temperatures*, not to make it get "thicker" than the first number. There is a difference. It's not making it get thicker, it's keeping it from getting too thin, get it?

So what does this mean? Yes, 5W-20 oil will flow like a 5W oil when cold, and will not thin any more than a 20W oil when hot. But it's cSt reading (i.e. viscosity) is much, MUCH higher when cold than when hot."

 

[JAG]

Here's how an oil gets classified by viscosity grade. http://www.infineum.com/information/viscosity.html

 

[Vilan]

Sounds like quite a good explanation to me.

 

[LouDawg]

Thanks. I've been trying to educate someone on another forum who keeps arguing that the first number, e.g. 5W-, means that it's thinner when it's cold. The he says the polymers help it thicken up to protect the engine better when it gets hot.

This is the last thing I wrote to him, then I'm done:

Gosh, I just don't know how to say it any more clearly to convince some people: cold oil is thicker than hot oil. Let's use PP 5W-20 as an example. All the first number (5) means is this:

1. It's made from a 5 weight base oil.
2. They add polymers to it so that when the oil heats up, it won't *thin out* to any less than a 20 weight oil, because the polymers straighten out as the oil heats up to help give it some "beef".
3. When it cools down from 212 F even only to 100 F (which is still pretty warm), it's over 5 times thicker than it is at 212 F.
4. Yes, it will flow better when cold than a 10W, or 15W, or 20W, or anything higher. But it will still flow MUCH more poorly than when the oil is hot.
5. You don't even want to know how much thicker it is at 0 F or -40 F. But here's a hint: it ain't running like water.

 

[Gary Allan]

Yep. Most state it in a misleading manner .. if they really know what they're talking about.

I make sure that the person realizes that 5W is like motor honey at the cold spec. If you just say "I acts like a 5 weight (if there was a 5 weight) @-30 ..they can think that it pours like water when cold. If you also said that it acts like a 40 weight @ 100C ..they again can think that it "got heavier" over the span from very cold to very hot. They keep looking at it like it is in the bottle when looking at both ends of the statement.

 

[Dad2leia]

I would say that if he still doesn't get it after that explanation, he probably wouldn't get it if the answer dropped a rod onto his driveway from using the wrong oil at the wrong time

.

 

[cfromc]

Tell him to drain his oil when its hot and then compare that to the fresh "cold" oil that he pours in from the bottle. Ask him, which is thinner? If its the stuff from the bottle, he's got problems.

 

[Tempest]

Quote:

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It's made from a 5 weight base oil.

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This is not correct. 5W30s for example are usually made from ~20wt base oils and then "plumped up" to a 30wt with VII. This is why 5W30s shear to a 20wt and not a 5wt.

They can get the 5wt rating by using PPD (Pour Point Depressant) which inhibits wax crystal formation at low temps, so it flows better at lower temps than it should.

 

[LouDawg]

Quote:

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Quote:

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It's made from a 5 weight base oil.

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This is not correct. 5W30s for example are usually made from ~20wt base oils and then "plumped up" to a 30wt with VII. This is why 5W30s shear to a 20wt and not a 5wt.

They can get the 5wt rating by using PPD (Pour Point Depressant) which inhibits wax crystal formation at low temps, so it flows better at lower temps than it should.

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Okay, thanks for clarifying that. I was aware of PPDs but didn't realize they were used to achieve the cold-temperature viscosity.