oil density specification

[bonjo]

I am trying to figure out how to interpret the low temperature performance of engine oil from published specification of the oil manufacturers. In particular how quickly the oil flows to all parts when cold starting and engine say at 10deg Celsius.

viscosity @ 40 being the first point of reference, what about the density quote such as "xxx@15"?

If for example two different oils have the same viscosity spec @ 40 but different density specs, then which one would have a better cold flow?

 

[Shannow]

Pump is volumetric, galleries are empty, and full of air...at 10C, they are all pumpable, and will therefore fill the gallieries at the same time...

Note that this isn't me saying that SAE60 is going to, just that in the realm of 0W through 15W, 20 through 40, normal passenger car grades at 10C it's a wash.

 

[bonjo]

so say at zero celc (freezing temp) a 0.895 density oil will have the same fluidity as one quoted @ 0.856?

Assuming all other parameters are the same (viscocity, additives, type and so on)

 

[FCD]

At above freezing temperatures, really any viscosity oil, even an SAE 60 will flow "adequately" well, only when you start getting into below freezing temperatures do the XXW- numbers come into play.

 

[weasley]

Density is built into the kinematic viscosity result (KV = dynamic viscosity/density). Forget about density.

 

[BrocLuno]

#1 Flow is not lubrication. Flow is delivery. There are other forms of delivery like splash and sling. Pumped oil is important to those components that can not get splash and sling oil. But piston skirts, rings, timing chains and timing gears generally do not get pumped oil.

So, to me there are two important considerations: 1.) how robust is the residual oil film that must lubricate until "new" oil is available; and 2.) how quickly will cold oil be thin enough to be slung to critical areas.

At the temps you are talking, most any modern multi grade oil will do both adequately

 

[ndfergy]

The higher the SG the greater the oil holds contaminants in suspension.

 

[Garak]

Originally Posted By: FordCapriDriver
At above freezing temperatures, really any viscosity oil, even an SAE 60 will flow "adequately" well, only when you start getting into below freezing temperatures do the XXW- numbers come into play.

Happy Birthday to you!

And yes, even a 20w-50 is technically a monograde, and can work under a lot of "winter" conditions. Here, not so much.

 

[SonofJoe]

Contrary to what Brother Weasley says, you can actually tell a lot about an engine oil from it's density, although you have to know what you're looking for and the significance of very small differences.

The density of performance additive (the DI) and solid VII in any oil are always much the same. For a given viscosity grade (eg 5W30) and a given performance level (eg GF-5) you can sort of treat the contributions from the DI & VII as being a constant. Therefore any differences in density you see are purely down to the mix of base oils you have in the oil.

Now the great bulk of multi grade oils contain at least two base oils; one with low viscosity and more volatile (with low density) and one that is heavier with a lower volatility (with high density). So for a given grouping of oils, generally you want to go for the one with the highest density to minimise the base oil Noack contribution.

You also need to know that for a given base oil viscosity, synthetics have a higher density than mineral oils. So for a given oil grouping, by picking the oil with the highest density, you're generally picking the oil with the highest synthetic content. If memory serves, PAOs have a greater density that Group IIIs so this too favours picking the oil with the highest density.

Just remember you're looking for very small differences, not big ones, and that you can't compare the densities of very disparate oils (ie don't try comparing densities if a 0W20 and 20W50).

Hope this helps...

 

[Shannow]

I do agree with Joe here, it's one of the things that I use to differentiate products in the same "category".

Originally Posted By: ndfergy
The higher the SG the greater the oil holds contaminants in suspension.


hmmmmmmmmmm.....i don't think that the drift towards the bottom of the sump after turning off is going to be materially different between engine oils of different grades...it's not like water and mercury.

The brownian motion keeping super fine particles in suspension is going tp be more affected by viscosity than density.

 

[zeng]

My perception is mineral oils (of higher KV@40*C) has higher densities than full synthetics (of lower KV@40*C) whilst KV@100*C of both are similar or neck to neck in similar grades of xWYY , what gives ?

 

[Jetronic]

full synthetic base oils from grIII only come in a narrow viscosity grade: typically 4-6 cSt @ 100°C. That's what most synthetics are made from.... the better ones have PAO and esters which exist in higher viscosities.

 

[ndfergy]

You also need to know that for a given base oil viscosity, synthetics have a higher density than mineral oils

Thanks for that clarification SonofJoe, I thought it was the other way around.

 

[ndfergy]

Originally Posted By: Shannow
I do agree with Joe here, it's one of the things that I use to differentiate products in the same "category".

Originally Posted By: ndfergy
The higher the SG the greater the oil holds contaminants in suspension.


hmmmmmmmmmm.....i don't think that the drift towards the bottom of the sump after turning off is going to be materially different between engine oils of different grades...it's not like water and mercury.

The brownian motion keeping super fine particles in suspension is going tp be more affected by viscosity than density.


It's been years since my high school chemistry so I must admit I had to research Brownian Motion. Although it doesn't apply with particles greater than 1 micron your point is taken. Viscosity is the determinate factor. Although density and viscosity are separate properties, wouldn't within the same compound, oil molecule, higher densities equate to higher viscosities? I'm sure in the grand scheme it's a hill of beans moving more towards sedimentation, but still, I'm curious.

 

[userfriendly]

Of course temperature would play a big part in sedimentation/time being, colder is thicker = more time it takes.
It appears that formulated mono-grade engine oil density peaks out at .910