[Vettezuki]

Originally Posted by enkeivette

Still don't understand why the oil gets thicker when hotter.

I read Adam's post about the polymers getting longer, but if weight it simply a measure of how long it takes the oil to flow through an orifice, I can tell you right now that hot oil comes out of the oil pan faster than cold oil.

And from Brian's chart, it also looks like oil gets thinner as it gets hot.

My understanding is as follows:

The polymers unwind with temperature, increasing film strength. The oil BEHAVES as though it were a heavier weight at the higher temperature.

The multi weight means that it flows as a 10 weight would at low temps and as a 30 weight would at the higher temperature. (Of course a hot 30 weight is thinner to the touch than a cold 10 weight.) This split personality is the point of a mutli-grade oil. It offers the operating temp protection of a 30 weight, but without the very thick nature of a 30 weight at start up (especially in a cold winter climate).

[BRIAN]

Originally Posted by enkeivette

Still don't understand why the oil gets thicker when hotter.

I read Adam's post about the polymers getting longer, but if weight it simply a measure of how long it takes the oil to flow through an orifice, I can tell you right now that hot oil comes out of the oil pan faster than cold oil.

And from Brian's chart, it also looks like oil gets thinner as it gets hot.

Okay this is VERY difficult to explain without going into fluid dynamics and all that mubo jumbo as it is very confusing. Took me lots of time to think about it in my head before it finally clicked when I first looked into it. Please bare with me on this.....

The way the bottles are numbered with there 5w-30's and 10w-30's which by the way is a very dated way to describe them is by lab tests done at different temperatures. For this purpose I just want to talk about your normal daily driven car, not your drag queens.

Okay so let me begin with the thickness levels. Automotive designers for the most part aim for an operating temperature of 212F (oil and water), with an oil thickness of 10. This is NOT the weight of the oil, IGNORE all that shit you read on the bottle for right now. 10 is the viscosity of the oil NOT weight, if our oil was 10 all day long regardless of temperature it would be having a ball. There would be almost no wear and tear on the motor and you wouldn't even need to warm it up, just start that baby up and step on the gas. Unfortunately that's not how it works.

I remember this example vividly but can't find a link I had GRRRrr. The example is you drive from work back home and your oil warms up to it's operating temp and all reaching the viscosity of 10. You come home you park and the oil cools and thickens over night. The next morning it's a viscosity of 150, super thick for start up temps. So now your thinking lets get the thinnest oil money can buy, well good luck finding something like that, remember as it warms up it get thinner. We don't want your oil turning into ignitable fumes now do we

I forgot to mention, your motors sees the most wear upon start up. The thinner it can be the better when cold. A 10W-30 would be about a 100 at 75F if I remember correctly and 10 at operating temp (212). We want to be as close as possible to 10 when cold but like I said this isn't a perfect world. Now a 0W-30 on the other hand would be about a 40 on cold start up and a 10 just like the 10W-30. Yeah the 40 isn't a 10 but it's damn sure closer than 100 which means less wear on start up, get it??????

I'm out of time, got class in a bit. This goes on much more deeper but I think if you put your mind to it you might be able to see it in your head. I'll finish this later tonight don't worry

[BRIAN]

I'm surprised nobody has responded, I'll let it sink in longer lol.

Here's the correct answer to what the "W" stands for. Straight from the ASE
http://www.focfloridaregion.com/edu/chapter7.htm



oh oh that's the same article I have from Dr. Haas, sweet. I have it in a file. Read all of that and you'll understand much much more than what I have explained!!! I didn't realize it. My professor emailed me to search for SAE j300 and tada got more than I asked for.

[Damian]

I just dont like how there is no real standard. You should be able to go in to a store and get 5W30 and actually get 5W30, regardless of the brand. I use Mobil 1 5W30 in all my cars and they seems to be doing just fine. My Eclipse had 130k miles on it, warped the heads, and the cylinder walls still had the factory honing on them. So Im assuming the oil is doing its job.

[enkeivette]

Originally Posted by BRIAN

I'm surprised nobody has responded, I'll let it sink in longer lol.

Here's the correct answer to what the "W" stands for. Straight from the ASE
http://www.focfloridaregion.com/edu/chapter7.htm



oh oh that's the same article I have from Dr. Haas, sweet. I have it in a file. Read all of that and you'll understand much much more than what I have explained!!! I didn't realize it. My professor emailed me to search for SAE j300 and tada got more than I asked for.

I was waiting for you to finish, I still don't get it.

[Vettezuki]

Originally Posted by enkeivette

I was waiting for you to finish, I still don't get it.

Multi-weight oils have different weight-characteristics according to temperature.

Repeat that like a mantra. It will come to my child.

Think of it as a two dimensional spectrum moving from "like the LOWER weight AT LOWER TEMP " to "like the HIGHER weight AT HIGHER temp"

[Vettezuki]

DISCLAIMER: This is my understanding. I hope it is basically correct. The following graph is not scientific; it is only intended to represent a relationship of parameters.

NOTE:
A 100 weight at 0C (32F) is going to be damn near a solid.
A 0 weight at 100C (212F) is going to be damn near like water.

THEREFORE:
- A Straight 10 weight oil at 100C is thinner than a straight 30 weight at 100C.
- Conversely, a straight 30 weight is thicker at 20C (68F) than a straight 10 weight at 20C.

The following graphs really need a 3rd dimension like a gradient, to help visualize thickness (what you perceive when you smear oil between your fingers). So use your imagination.

This is what a straight 10 would look like. Nice thinness for starting but too thin at operating temp.



A straight 30. Fine for operating temps, but pretty damn thick during startup, not offering a lot of protectino until the engine gets warm.



Behold the miracle of blended multi-weights and unwinding polymers. This graph is intended to show what a 10/30 oil might behave like on a typical day in CA where you start up at around 20C (68F) in the morning and bring up to something like a typical operating temp.



THIS IS THE POINT of a multi-grade oil. Relatively thinner at cooler (startup temps) and relatively thicker at operating temps. The real point is that something like a 10-30 offeres the protection of a 30 weight oil at operating temps, but offers lighter, easier starrting, quicker to lubricate, characteristics at startup temps.


BONUS:
Assuming a fairly static relationship, a 10 weight @ 20C will flow like a 90 weight @ 100C.

Simply stated, a multi-weight oil is just a way of optimizing lubricating characteristics according to two principle conditions; starting and running.

[enkeivette]

Ben, thanks for laying it out for me. I get what you're saying, just having a hard time buying it.

If weight is simply a measure of how long oil takes to drain through an orifice, the longer the thicker, than from my experience of doing hot and cold oil changes with 10w 30, it seems to me that this is false. Like I said, drains faster when hot. Using my oil drain plug as an orifice, it seems to me that hot 10w 30 is thinner than cold 10w 30. Which is obviously contrary to what you explained.

I could see making the case that the hot 10w 30, acts like a thick oil in some way even though it flows faster, but then how would you measure it? If weight is just a measure of flow vs. time... how do you measure how the oil 'acts?'

And really thanks again Ben and Brian for taking your time to lay it out.

[Vettezuki]

Originally Posted by enkeivette

. . Using my oil drain plug as an orifice, it seems to me that hot 10w 30 is thinner than cold 10w 30. Which is obviously contrary to what you explained.

It is not contrary.

TEMPERATURE, TEMPERATURE, TEMPERATURE

Stare at the charts above. Note, weight, temp, thick and thin (and the fact I'm not completely representing the thick/thin part witha gradient or Z dimension). Remember I said a 10@20C while have a thickness like a 90@100C. Also keep in mind the charts are only intended to show relative thickness according to weight and temp.

The difficult part to understand is that the nature of a multi-weight oil is changing with temp. It's not thicker at higher temps, it behaves like a heavier oil at higher temps.

A hot 10 is thinner than a cold 10.
A hot 30 is thinner than a cold 30.

Depending on temps, a hot 30 is thinner than a cold 10. That's why as you stated, a hot 10/30 is thinner than a cold 10/30.

THE POINT of a multi-weight is that when hot it's acting more like a 30 at said higher temp, and when cold, more like a 10 would at said lower temp.

If it were a straight 10, it would be even thinner than 10/30 when hot. Maybe think of that way.



Or, another way, the point of a multi-weight:
A cold 10 is thinner than a cold 30. (GOOD)
A hot 30 is thicker than a hot 10. GOOD)

Best of both worlds.

(COLD) Like a 10 ------------------------------------------> Like a 30 (HOT)

The oil is NOT becoming thicker in absolute terms with an increase in temperature, it's just thicker than it would have been if it was a straight 10 for example.

In fact, in all cases it's going from relatively thicker to relatively thinner with temp in absolute terms. It's the spread that matters. A multi-weight allows the range to be constrained.

If it were a straight 10

(COLD) GOOD ----------------------------------------------> BAD - Too Thin (HOT)

If it were a straight 30

(COLD) BAD - Too Thick ------------------------------------------------> GOOD (HOT)

multi-weight 10/30

(COLD) GOOD -----------------------------------------------> GOOD (HOT)


Ok, I'm running out of ways to say the same thing.

[BRIAN]

Vettezuki is doing a good job explaining it with the numbers on the bottle. Those numbers are the ones that threw me off in the beginning so I try to avoid it all together, but I get your explanation perfectly.

Like I said it's very confusing, I asked the same questions and of course I too wasn't buying it. The problem is the numbers on the bottle throw you off, that whole 10W-30 junk. Your thinking, yeah because the 10W is smaller than 30 it should feel thinner to the touch when cold and thicker when hot. The bottles should be labeled with there thickness instead for example a 10W-30 I would label it more like 100-10, thickness of 100 when cold and 10 when hot or operating temp.

There would be chaos in the streets if that happened today, probably why they just keep on going with there weight system.