Density of motor oil

Patman

Patman

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The one thing that always seems to come up when looking at the technical data of an oil is density. What does this even mean and why would we care about it? It’s always felt like a meaningless piece of information to give us.
 
I believe it’s density compared to water. How would this be useful to a BITOGer? Well, if a a type of motor oil had a density of .85 that would mean a liter of motor oil would weigh 850 grams. If you want to be very particular and get a pretty precise volume of oil you could convert quarts to liters, and dispense the needed grams into a pre-weighed, empty container on a kitchen scale. Extreme? Maybe, but I do it…
 
Danh said:
I believe it’s density compared to water. How would this be useful to a BITOGer? Well, if a a type of motor oil had a density of .85 that would mean a liter of motor oil would weigh 850 grams. If you want to be very particular and get a pretty precise volume of oil you could convert quarts to liters, and dispense the needed grams into a pre-weighed, empty container on a kitchen scale. Extreme? Maybe, but I do it…
Click to expand...
But wouldn’t all motor oils basically have pretty much the same density? It seems like all of them are very close to.85
 
Patman said:
But wouldn’t all motor oils basically have pretty much the same density? It seems like all of them are very close to.85
Click to expand...

Density matters when converting from kinematic to dynamic viscosity, and not all base oils have the same density. Mineral oils are in the mid 0.8 range, PAO tend to be below 0.8 (so for the same kinematic viscosity they have less dynamic viscosity) and esters tend to be heavier, POE close to 1. since all oils are basically mixes of different base oils they tend to settle close to 0.85 density. HTHS viscosity is dynamic, as are CCS and MRV.
 
Technical data, meaning SDS sheet?
If so, that data is meant for first responders or cleanup personnel, likely others may need that info. Same as volatility. Not that it's an issue with motor oil, but according to the rules set forth by the EPA, it's required to be on the SDS sheet for various reasons.
It matters witch data you are talking about. :unsure: I don't see it being beneficial to the average user.
 
JohnnyG said:
Technical data, meaning SDS sheet?
If so, that data is meant for first responders or cleanup personnel, likely others may need that info. Same as volatility. Not that it's an issue with motor oil, but according to the rules set forth by the EPA, it's required to be on the SDS sheet for various reasons.
It matters witch data you are talking about. :unsure: I don't see it being beneficial to the average user.
Click to expand...

also sds, but product data sheet was meant
 
JohnnyG said:
Technical data, meaning SDS sheet?
If so, that data is meant for first responders or cleanup personnel, likely others may need that info. Same as volatility. Not that it's an issue with motor oil, but according to the rules set forth by the EPA, it's required to be on the SDS sheet for various reasons.
It matters witch data you are talking about. :unsure: I don't see it being beneficial to the average user.
Click to expand...
I wasn’t talking about the safety data sheet, but the technical data such as viscosity, flashpoint, pour point, etc
 
When you buy a litre of oil, are you buying it by weight or volume?
A cubic meter of water (1,000 litres) weighs 1,000 kilograms, or one kilogram per litre.
But, your 5w20 only weighs 85% of water, so is the volume greater per litre or do you get one thousands of a cubic meter of oil?
If the latter, a litre of SAE 40 that has a specific gravity of .900, or 90% of water should weigh about 5% more than 5w20.
 
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userfriendly said:
When you buy a litre of oil, are you buying it by weight or volume?
A cubic meter of water (1,000 litres) weighs 1,000 kilograms, or one kilogram per litre.
But, your 5w20 only weighs 85% of water, so is the volume greater per litre or do you get one thousands of a cubic meter of oil?
If the latter, a litre of SAE 40 that has a specific gravity of .900, or 90% of water should weigh more.
Click to expand...
What does it say on the front of the container?

Density is reported for shipping information and for firefighters.
 
Jetronic said:
Density matters when converting from kinematic to dynamic viscosity
Click to expand...
Bingo. dynamicViscosity = density x kinematicViscosity
For a given KV, increasing density increases DV. Red Line and some other oils with quite a bit of esters are denser than most. Higher viscosity oils tend to be denser, if VII concentration is held constant. Kinematic viscosity matters when it drains down under the force of gravity. As you said, mostly it is dynamic viscosity that matters in an engine. The density variations of motor oils are not very large though. Plus or minus a few percent would contain the vast majority.

This article is really good. https://www.machinerylubrication.com/Read/294/absolute-kinematic-viscosity
 
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userfriendly said:
When you buy a litre of oil, are you buying it by weight or volume?
A cubic meter of water (1,000 litres) weighs 1,000 kilograms, or one kilogram per litre.
But, your 5w20 only weighs 85% of water, so is the volume greater per litre or do you get one thousands of a cubic meter of oil?
If the latter, a litre of SAE 40 that has a specific gravity of .900, or 90% of water should weigh about 5% more than 5w20.
Click to expand...

At what temperature?
Change the temperature of the water, oil, etc even just 0.1 Centigrade, and the weight changes per 1000 liters.
 
Jetronic said:
Density matters when converting from kinematic to dynamic viscosity, and not all base oils have the same density. Mineral oils are in the mid 0.8 range, PAO tend to be below 0.8 (so for the same kinematic viscosity they have less dynamic viscosity) and esters tend to be heavier, POE close to 1. since all oils are basically mixes of different base oils they tend to settle close to 0.85 density. HTHS viscosity is dynamic, as are CCS and MRV.
Click to expand...
Rotational viscometers such as HTHS, MRV and CCS report apparent viscosity which is derived from a torque value. There's no conversion from kinematic.
 
userfriendly said:
When you buy a litre of oil, are you buying it by weight or volume?
A cubic meter of water (1,000 litres) weighs 1,000 kilograms, or one kilogram per litre.
But, your 5w20 only weighs 85% of water, so is the volume greater per litre or do you get one thousands of a cubic meter of oil?
If the latter, a litre of SAE 40 that has a specific gravity of .900, or 90% of water should weigh about 5% more than 5w20.
Click to expand...
Don’t overthink it. The litre is defined as a unit of volume.
 
I literally own, and drive fuel trucks.
If i put 46,000 liters of gas in the trailer when its warm, and park it outside overnight at 25 below, it has shrunk in volume in the trailer, bu the weight remains the same.
If i put 46000 liters of gas in a trailer on a cold morning, then drive it 10 hours somewhere in the heat and blazing sunshine, it has expanded in the trailer, but the fuels weight remains the same.

Lets use water next, get a metal tub that holds exactly 1000 liters of water when full to the top. Fill it with a garden hose of cool water, lets say 5 C water temperature. Then let it heat up on a hot sunny day, it expands, some water spills out over the top as it expands.
Its still 1000 liters in volume, but now weighs less than the cold water you put in.

It's not rocket science.
 
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