Specific gravity and density

[mjoekingz28]

Do these comingle like rake and trail on a motorcycle?


Example

5w-20. 5w-30. 10w-30

.861. .861. .871
SG @60F

7.18. 7.18. 7.26
D lb/gal



And while we are at it, I had an argument with my 1st cousin about 15 years ago about ounces and fluid ounces. I said ounces are by weight, but fluid ounces were volume. He stated fluid ounces are just ounces (of weight) in liquid form.

Researched, asked my Trigonometry teacher- always kind of wondered.




What brings this up is I was asking someone is nitromethane light or heavy. I said gasoline is lighter than water as you can drain the water from underneath a wing. Then he brought up SG.

Thanks

 

[Shannow]

Specific Gravity is density in Kg/L, or the ratio of the fluid to water (which is 1Kg/l)

Density (in S.I.) is usually Kg/m^3

 

[Jetronic]

specific gravity of an oil is determined by it's chemistry. There's no real correlation between the baseoil viscosity and the final product's specific gravity due to the polymers added

I've found esters are usually on the heavy side, close to or even over 1. but you can't find this in a finished product 95% of the time.

 

[Astro14]

Your cousin is a moron who clearly doesn't remember 4th grade earth science in which he should have learned what is meant by weight, and what is meant by volume.

He doesn't happen to be a TSA agent, does he?

I've found several of them who are equally ignorant...

 

[SHOZ]

Get the free software called Convert. Very handy.

https://joshmadison.com/convert-for-windows/

 

[Tom NJ]

Just to clarify, density is different than specific gravity (SPG), although related. Density is the mass per unit volume of a material at a given temperature. For a fluid this is often expressed as g/ml or kg/l or lbs/gal. Since volume is a function of temperature, the measurement temperature must be noted to be meaningful, such as 0.85g/ml @ 15°C.

Specific gravity is a ratio of the density of a material over the density of water, and as such does not have units. Since the densities may have been determined at different temperatures, both measurement temperatures must be noted. For example, for a fluid the SPG may be expressed as 0.85 15°C/15°C if both densities were run at 15°C, or as 0.85 15°C/4°C if the fluid density was run at 15°C and the water density at 4°C.

Density, and therefore SPG, are greatly affected by chemistry. For example, the density of most POE base oils fall between 0.94 and 1.01 @ 15°C, while the density of most PAO and Group III base oils fall between 0.81 and 0.85 @ 15°C. Group 1 mineral oils are a little heavier than PAOs due to their aromatic content, and diesters are a little lighter than POEs due to having fewer oxygen atoms and less polarity. The polarity of esters causes intermolecular attractions which increases the density. Motor oil additive packages have high densities due to the metal content in the detergents. For reference, the density of water is 1.000 @ 4°C, which is the temperature at which water reaches its highest density (actually 3.98 but who's counting).

The densities of other common materials in g/ml (or g/cc) are:

Air = 0.0013
Aluminum = 2.7
Steel = 7.8
Lead = 11.3
Gold = 19.3
Platinum = 21.5

Tom NJ

 

[Garak]

From a mathematical perspective, specific gravity will correspond nicely with density, assuming your density numbers are using cgs units, which tend to be quite common in undergrad chemistry labs. Of course, as has already been pointed out, specific gravity itself is dimensionless.

 

[userfriendly]

You have 2 engine oils, a multi grade with a density of .850 and a single grade with a density of .900

Your engine with 9.5 liters of the multi grade oil reads full on the dipstick.

Would approximately 10 liters of the single grade engine oil be required to read the same level on the dipstick?

 

[MolaKule]

Originally Posted By: Tom NJ
Just to clarify, density is different than specific gravity (SPG), although related. Density is the mass per unit volume of a material at a given temperature. For a fluid this is often expressed as g/ml or kg/l or lbs/gal. Since volume is a function of temperature, the measurement temperature must be noted to be meaningful, such as 0.85g/ml @ 15°C.

Specific gravity is a ratio of the density of a material over the density of water, and as such does not have units. Since the densities may have been determined at different temperatures, both measurement temperatures must be noted. For example, for a fluid the SPG may be expressed as 0.85 15°C/15°C if both densities were run at 15°C, or as 0.85 15°C/4°C if the fluid density was run at 15°C and the water density at 4°C.

Density, and therefore SPG, are greatly affected by chemistry. For example, the density of most POE base oils fall between 0.94 and 1.01 @ 15°C, while the density of most PAO and Group III base oils fall between 0.81 and 0.85 @ 15°C. Group 1 mineral oils are a little heavier than PAOs due to their aromatic content, and diesters are a little lighter than POEs due to having fewer oxygen atoms and less polarity. The polarity of esters causes intermolecular attractions which increases the density. Motor oil additive packages have high densities due to the metal content in the detergents. For reference, the density of water is 1.000 @ 4°C, which is the temperature at which water reaches its highest density (actually 3.98 but who's counting).

The densities of other common materials in g/ml (or g/cc) are:

Air = 0.0013
Aluminum = 2.7
Steel = 7.8
Lead = 11.3
Gold = 19.3
Platinum = 21.5

Tom NJ

 

[userfriendly]

Is engine oil sold by volume or weight?
For example would a higher density product not fill a 5 gallon pail to the same level as a lower density product?

I own an engine that takes 10 liters of oil.
I buy a 20 liter pail of a high density engine oil.
Will I have enough oil for two oil changes?

 

[Nyogtha]

Liters (and fractions & multiples thereof), and quarts (and pints and cups and gallons and barrels), are measures of volume.

Your 20 liter pail if full to 20 liters will contain two 10 liter portions.

A heavier oil will need a higher pressure to travel from the sump to the top of the engine than a lighter oil. This is due to gravity. This will be difficult to see on your oil system gauge due to the effects of viscosity.

A heavier oil will flow more quickly from the top of the engine to the sump, again due to gravity. Again, this would be very difficult to see relative to the effects of viscosity.

Hydrostatic head is a function of differential density (oil vs. gases in the valve covers) and differential elevation.

Since your engine has a positive displacement oil pump this doesn't really matter since by definition it delivers a certain volume flow rate per revolution. Viscosity, in its simplest terms, is resistance to flow. So pressure at the oil pump discharge depends on the resistance developed through the circuit. As the oil warms, its viscosity decreases (as well as its density), resistance to flow within the fluid reduces (but the circuit stays the same), and oil pressure at the oil pump discharge reduces for a given pump speed (which is proportional to engine speed). However the change in density over the temperature change (say in %) will be very small relative to the change in viscosity over this temperature range (again say in %).

If you had a centrifugal oil pump the relationship between density, viscosity, pressure developed, speed, and energy required to pump a given flow rate would be more complex.

This is a simplification but a reasonable one without going into minutae on positive displacement pump efficiency. whether the relief circuit is open or partially open, etc.

 

[userfriendly]

You answered my next question with (shortened);

"The change in density over the temperature change will be very small relative to the change in viscosity over this temperature range".

I'm going down a path, and I'm not sure where it is leading us to, or why.

Obviously the density decreases as temperature rises, expanding the volume.
We can see that on the dipstick.

 

[Nyogtha]

Correct!

Checking level on an automatic transmission dipstick when cold vs. at operating temperature illustrates this very well.

 

[Shannow]

Originally Posted By: Nyogtha
This is a simplification but a reasonable one without going into minutae on positive displacement pump efficiency. whether the relief circuit is open or partially open, etc.


But that's where they always end up

 

[userfriendly]

Lol.

If we compare two engine oils, one with a higher flash point than the other.

Will the higher flashpoint oil expand less (retain it's density) when heated and therefore retain viscosity better?

 

[Nyogtha]

Depends : flash point varies quite quickly with differences in composition.

I've seen just a little bit of gasoline throw a whole bunch of diesel off-test. It's an extremely difficult property to blend off once it's out of spec.

You have no idea how many formally educated individual who work their way into management I've had to explain this to, as well as highly educated fresh out of school folks. Not all listen equally well, with directionally proportional outcomes.

 

[userfriendly]

No, I get it, especially when tank cars go off the rails.
The 5% of low boilers cause 95% of the problem.

I talked to one Bakken crude guy from Minot ND the other day about this. He is quite confidant that in the near future the light ends will be removed and piped away as they do in Texas prior to shipping by rail.

 

[userfriendly]

Back to engine oil....

I'll assume the oil remains non compressible, at least for our application, up to the flash point, vapor point or close to it.

Higher oil pressure will help the oil retain it's density by raising the boiling point thus preventing gas bubbles from forming in the oil galleries.

Once again, I'm not sure where I am going with this.
Maybe NOACK?

 

[Nyogtha]

At the extreme end, I've seen pitch from a supercritical deasphalting unit, which is about the furthest you can go in refining oil without turning it into solid coke, throw off flash in heavy fuel oil blend because of entrained / dissolved isobutane solvent having to go through goo that while quite hot, was still quite thick. The was a vapor recovery compressor piped to the pitch tank vent.

The normal boiling point of isobutane is 11°F, this tank was always kept above 275°F.

There was quite a bit of density and vapor pressure difference between the isobutane and pitch to make the light stuff get to the surface and vaporize, but that pitch was really viscous.

 

[userfriendly]

The end result would be an environmentally responsible asphalt and butane?

I think I have it figured out where I was going with the density thing.

Low VI mono-grade engine oils appear, as a group to have both a higher flash point and density than the high VI multi-grade engine oils.
They also as a group, have lower NOACK and an improved correlation between KV100 and HTHS.

Can you add to this?