Oil Density

[Shel_B]

The PDS sheets for many oils show the lubricant's density. What, if anything, does an oil's density contribute to its quality as a lubricant? Would, for example, an oil with a greater density have better lubricating qualities than a similar, less dense, oil? Put another way, why show the density at all?

 

[Wheel366]

Completely unrelated but when I saw the word density, this is what came to mind. I've got issues...

 

[dnewton3]

It would be too hard to correlate the density to "lubricating qualities" because those "qualities" are very broad and hard to define.

It may be possible to correlate density to viscosity? I don't know, but at least those would be easily measured values that can be tabulated and graphed.

However, I suspect that density has little to do overall with any perceived benefit in the real world. We can see that as long as the MOFT is maintained, in combination with a decent additive package, that vicosity has minor influence, if any at all. For example, a 5w-20 vs 5w-30 in many applications will result in wear rates and trends which are statisitcally indistinguishable. So I suspect that oil density is even more removed and won't be able to be classically detected in differential.

 

[Tom NJ]

Density is listed in data sheets because it important for several reasons. A key factor is that lubricants are usually sold by volume, but many ingredient, manufacturing, and shipping costs are expressed in weight. Density is needed to convert weight to volume. From a performance standpoint density can affect pumping efficiency, the suspension of free water and particles, heat transfer, and is needed in some viscosity conversions. It is also used as a fast and cheap quality control test.

Polarity affects density and therefore to some extent density may give some indication of polarity, although I would not expect a clean correlation due to other variables. Polarity causes molecules to be attracted to each other and thereby packs more molecules into a given volume, increasing density. This can be seen in the density of various base oils with different polarities. PAO has no polarity, while Group I base oil has some polarity, diesters more, and POEs more yet.

Approximate Density of 5 cSt Base Oils
PAO = 0.82
Group I = .87
Diester = 0.91
POE = 0.99

In the lubricant ester family where polarity and densities vary greatly (0.86 to 1.01), I often used density as a factor in identifying the chemistry in unknown products.

 

[Foxtrot08]

Grease and gear oils are all sold in pounds. Other metal working products are often sold in pounds. Trucks are scaled in and out, weighed in pounds when loaded. Also metered on. Some bottle filling lines - things are weighed.

Etc. So it’s important in the transportation and sales of product.

Edit:

We check our Drums / Kegs / 5 gallon buckets that are filled on a certified scale. It’s also used for meter testing purposes on delivery trucks.

Lots and lots of reasons.

 

[DirectRejection]

Awesome, Tom NJ !
I always thought density might indicate quality of basestocks.

 

[Shel_B]

Density is listed in data sheets because it important for several reasons. ....

Thanks, Tom. That was very helpful and informative.