Viscosity

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digginfool
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Viscosity

Post by digginfool »

Here's a question that I've thought about for a while and can't seem to find a solid answer anywhere. The fact that pretty much all of us live in Florida and a large portion lives in South Florida, is there any real reason to run a multi-vis oil? Wouldn't it make better sense to run a straight 30? Especially in the summer?
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Slidin Gator
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Re: Viscosity

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A multi grade oil is a better choice in both winter and summer. Multi weight oils have a higher viscosity index which equates to less change in viscosity versus temperature. Yes, the W grades have lower pour point and cranking temperatures vs. straight weight for winter cranking. However, oil weight selection is based on engine viscosity requirements at operating temperature, which is normally around 200 F or so. When cranking a "cold" engine on a 95 degree day, the oil viscosity is much higher than at operating temperature, on the order of 10X higher. Even in this situation the "W" grades are significantly closer to the proper viscosity than the straight weight.

Similarly, at operating temperature, the viscosity is more stable across the actual temperature range that the oil sees over the full oil circuit. Oil leaving the bearings and returning to sump is at the highest temp versus the oil coming out of the oil cooler (where the oil temp sensor is if you have one) and heading to the bearings. Depending on the oil routing, the oil temperature could see significant variation between different bearings (crank, rods, valves) etc. Multi-weight oils will stay in the proper operating range at higher oil temperatures that are likely to be seen in the summer.

I think the chart below (typical automotive specs) is as good of an example as anything else. Note that even the 0W-30 weight oil has a higher operating temperature than the straight 30 weight. This is not exactly the case for the 40 weight oils, the 0-10 "W" grades have a lower max temperature vs. the straight 40, 15 and 20 "W" grades, which is quirk of the SAE spec details. Finally, realize the the whole industry has pretty much switched to multi-grade oils. The only straight weight oil normally sold retail is SAE 30, which used to be cheaper than multi-grade, but since few use it anymore it is normally more expensive and never on sale.

I suggest using the highest "W" grade available for summer (or Florida year around), i.e., the 10/15/20 "W" grades. It should be a requirement to even sell the 0/5 "W" grades in Florida unless the buyer shows their Canadian drivers license and promises to leave the state soon :stirpot:

One last point, viscosity stability is one of the key features of synthetics vs. mineral oils. Synthetic oils require less viscosity modifier additives to meet the SAE viscosity specs. Viscosity modifiers are polymers that expand when heated to limit viscosity decrease with higher temperature. A 10W-30 mineral oil is roughly a 10 weight oil with modifiers to make it work like a 30 weight oil at operating temp.

Image
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

terrible ted
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Re: Viscosity

Post by terrible ted »

Hey that scale not in US standards so no one going to look at it.

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Re: Viscosity

Post by Rick McC. »

Yeah; WTF!
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Re: Viscosity

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Deano
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Re: Viscosity

Post by Deano »

They tried to convince us all the way back in elementary school that if we didn't learn to think in metric
we would be left behind. I'm glad to see that I'm not the only one that didn't buy that hook, line, and sinker. :)

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Last edited by Deano on Mon May 25, 2020 9:43 am, edited 1 time in total.
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Slidin Gator
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Re: Viscosity

Post by Slidin Gator »

Thanks Deano, if that makes everyone happy its awesome.
terrible ted wrote:
Sat May 23, 2020 9:12 pm
Hey that scale not in US standards so no one going to look at it.
Nothin for nothin Ted, but apparently you and Rick looked at it! :stirpot:

Tough crowd for sure, always getting hung up on the units.


The thing is, if celsius is an issue, it makes the whole viscosity discussion thing more difficult. The Society of Automotive Engineers is responsible for SAEJ300 covering engine oil viscosity requirements. The entire specification is written in metric units, not a Fahrenheit or SUS viscosity unit in sight.

A key parameter is viscosity at 100 Deg C, chosen because it is roughly the operating oil temp of many engines, plus it's the boiling point of water, an easy to reproduce reference point of 212 Deg F.

Read up on how Fahrenheit evolved, its a real British S*** show. One of the key reference points for the original scale was the temperature of the human body, we all know what a stable reference that is. :lol: :lol: :lol:


Image

A keen eye reading this chart will note that viscosity figures use different units at different temperatures (cP and cSt), so they do not directly compare. I didn't make the table, but there are reasons for this.
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

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Scotty1
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Re: Viscosity

Post by Scotty1 »

:rebel: Sounds like you fellows are talking Greek to me :scratch: :rebel:

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Slidin Gator
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Re: Viscosity

Post by Slidin Gator »

Scotty1 wrote:
Sun May 24, 2020 4:16 pm
:rebel: Sounds like you fellows are talking Greek to me :scratch: :rebel:
Scotty1, no doubt, a deep dive into viscosity can be a trip, let me move on to the middle of the story.

Back in the day, most engines were air cooled, Fahrenheit ruled and SAE stood for Society of Airboat Engineers. :cheers:

Back in the day, SAE 50 oil was rated for cranking at 50 F or higher (no metric).

Back in the day, all was good in airboating cause folks understood the value of warming an engine properly, ur gonna get there soon enough, the dry trails are faster.

Then along came CM guys, all the bling, polished blah blah blah. They avoid the AV crowd and usually compete with the Bass Tournament crowd, either way it's dump, thump and BLLAAAHHHHH. :cherry:

So back in the day, the SAE said, WTF we gonna do with these CM guys, they keep blowin up their sh*p and keep callin and bitchin. That's when they came up with multi weight oils, just to shut the dam CM guys up. :stirpot:
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

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Scotty1
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Re: Viscosity

Post by Scotty1 »

:rebel: Sounds like your :fishing and :stirpot: I am a cm guy and loving every minute of it there is just something special about hearing that V8 horse power roar and being able get my fuel easily any where. :cheers: :rebel: Oh and just good ole 10W 40 simple

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Slidin Gator
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Re: Viscosity

Post by Slidin Gator »

Scotty1 wrote:
Mon May 25, 2020 7:51 am
:rebel: Sounds like your :fishing and :stirpot:
You reckon?
Scotty1 wrote:
Mon May 25, 2020 7:51 am
Oh and just good ole 10W 40 simple
My point exactly, why didn't you just tell Diggin that initially?



I almost put my tranny pan back on without a filter thinkin about all this. Caught it just before firing up the gasket maker tube and putting on the gloves. :banghead: :banghead: :banghead:

Image
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

terrible ted
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Re: Viscosity

Post by terrible ted »

Slidin Gator wrote:
Sun May 24, 2020 2:02 pm
Thanks Deano, if that makes everyone happy its awesome.
terrible ted wrote:
Sat May 23, 2020 9:12 pm
Hey that scale not in US standards so no one going to look at it.
Nothin for nothin Ted, but apparently you and Rick looked at it! :stirpot:

Tough crowd for sure, always getting hung up on the units.


The thing is, if celsius is an issue, it makes the whole viscosity discussion thing more difficult. The Society of Automotive Engineers is responsible for SAEJ300 covering engine oil viscosity requirements. The entire specification is written in metric units, not a Fahrenheit or SUS viscosity unit in sight.

A key parameter is viscosity at 100 Deg C, chosen because it is roughly the operating oil temp of many engines, plus it's the boiling point of water, an easy to reproduce reference point of 212 Deg F.

Read up on how Fahrenheit evolved, its a real British S*** show. One of the key reference points for the original scale was the temperature of the human body, we all know what a stable reference that is. :lol: :lol: :lol:


Image

A keen eye reading this chart will note that viscosity figures use different units at different temperatures (cP and cSt), so they do not directly compare. I didn't make the table, but there are reasons for this.

I might have to work with it but otherwise I don't use it.

terrible ted
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Re: Viscosity

Post by terrible ted »

Slidin Gator wrote:
Sun May 24, 2020 2:02 pm
Thanks Deano, if that makes everyone happy its awesome.
terrible ted wrote:
Sat May 23, 2020 9:12 pm
Hey that scale not in US standards so no one going to look at it.
Nothin for nothin Ted, but apparently you and Rick looked at it! :stirpot:

Tough crowd for sure, always getting hung up on the units.


The thing is, if celsius is an issue, it makes the whole viscosity discussion thing more difficult. The Society of Automotive Engineers is responsible for SAEJ300 covering engine oil viscosity requirements. The entire specification is written in metric units, not a Fahrenheit or SUS viscosity unit in sight.

A key parameter is viscosity at 100 Deg C, chosen because it is roughly the operating oil temp of many engines, plus it's the boiling point of water, an easy to reproduce reference point of 212 Deg F.

Read up on how Fahrenheit evolved, its a real British S*** show. One of the key reference points for the original scale was the temperature of the human body, we all know what a stable reference that is. :lol: :lol: :lol:


Image

A keen eye reading this chart will note that viscosity figures use different units at different temperatures (cP and cSt), so they do not directly compare. I didn't make the table, but there are reasons for this.

Its a different language., I only read it at work otherwise I really don't pay any attention to it. I convert everything we did in physics when I took it. Everything converts.

terrible ted
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Re: Viscosity

Post by terrible ted »

9/5c+32=f

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Deano
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Re: Viscosity

Post by Deano »

terrible ted wrote: 9/5c+32=f
I found it interesting that at -40 degrees they measure the same.
Always knew they had to cross at some point, but never ran the math out that low.
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but it is not the path to knowledge; it has no place in the endeavor of science."
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Slidin Gator
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Re: Viscosity

Post by Slidin Gator »

After a few side tracks, I'm backing up to Mr. Diggin's original post.
digginfool wrote:
Mon May 18, 2020 8:17 am
Here's a question that I've thought about for a while and can't seem to find a solid answer anywhere. The fact that pretty much all of us live in Florida and a large portion lives in South Florida, is there any real reason to run a multi-vis oil? Wouldn't it make better sense to run a straight 30? Especially in the summer?
The real question is "what are the drawbacks of Multi-Weight oils?" To make a multi weight oil, they roughly start out with a thinner weight base oil and add viscosity modifiers - polymers - that increase the viscosity of the thin oil at operating temperature. But they wear out and the oil reverts back towards it's original weight (say SAE 20). Here are a couple of links with more discussion:
https://www.machinerylubrication.com/Re ... -improvers
Disadvantages

Unfortunately, viscosity index improvers do have some drawbacks. The primary disadvantage is they are susceptible to mechanical shearing. When referring to the slinky analogy, it is easy to imagine a stretched-out slinky cut in half by mechanical processes to produce two shorter slinkys.

As the additive is repeatedly sheared, it loses its ability to act as a more viscous fluid at higher temperatures. Higher molecular weight polymers make better thickeners but tend to have less resistance to mechanical shear. Lower molecular weight polymers are more shear-resistant, but do not improve viscosity as effectively at higher temperatures and, therefore, must be used in larger quantities.
https://itstillruns.com/differences-30w ... 86573.html
https://itstillruns.com/differences-30w ... 86573.html
Often, 30W motor oils contain a slightly higher quantity of viscosity-improving additives to create a thinner texture. These additives have their drawbacks. In high temperatures and pressures they "shear" or break apart, and can create a detrimental sludge, which reduces the engine's performance. Once the oil has begun this process of degrading, the rating changes from a 30W oil to a 20W or 10W oil.
So the point is under heavy use, straight weight oils will out survive multi-weights. This is one reason straight 30 is specified for lawn mowers, standby generators etc. I vaguely remember changing the oil in the lawn mower a few years ago??

Airboating involves a lot of starting and stopping, the oil heats up, the oil cools down. As long as you follow a reasonable oil change interval the oil is refreshed before the oil damage is significant. The result will be less wear and tear due to quicker warm up.

Synthetic oil base stock is more stable vs. temperature and therefore typically requires less of these additives. This is one of the reasons for the longer oil change interval.

I generated some viscosity curves using the data from the following Castrol data sheets for future reference.

https://msdspds.castrol.com/bpglis/Fusi ... nglish.pdf

https://msdspds.castrol.com/bpglis/Fusi ... v_2012.pdf

Image


The relationships are more clear when plotted on a log scale. At cold temp the SAE 30 is similar to 10W-40. It is not until about 175 F before the straight weight is in the same range as the multi weight 30's.

Image


Finally, zoomed in to the operating range.

Image
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

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