What spec determines if an oil is "heavy"?

[Blake1107]

I recently switched to Magnatec 5W30 and was comparing the information on the PDS's for Magnatec 5W20 and 5W30 today and some others just out of curiosity.

Some of the numbers between 5W20 and 5W30 were not really far off from each other and made me wonder. I have seen some say in some other threads that "such and such oil is heavy for a 5W20/5W30/0W20 etc."

So, what exactly or which spec exactly determines or makes one say a certain 5W20/30 is "heavy"?

 

[FowVay]

The numbers on the oil bottle simply represent a range of viscosity grades that the oil falls into. A XW-30 can range from 9.3cSt to <12.5cSt at 100ºC. So, an oil that has a kinematic viscosity of 9.5cSt would be a light XW-30 and a oil that had a kinematic viscosity of 12cSt would be a heavy XW-30 even though they'd both be labeled XW-30 on the bottle.

 

[PimTac]

Grades of oils fall into a range.

Viscosity Charts - Bob is the Oil Guy

Viscosities can be related horizontally only Viscosities based on 96 VI single grade oils. ISO are specified at 40°C AGMA are specified at 40°C SAE 75w, 80w, 85, 5w, & 10w specified at low temperature. Equivalent viscosities for 100° & 210°F are shown SAE 90 to 250 and 20 to 50 specified at...

bobistheoilguy.com

 

[Snagglefoot]

On all the manufacturers websites they should have Kinematic Viscosity at 100 deg C. You can make your decision from that. (among all the other features you want to look for in an oil.) This was touched on in the above two posts.

 

[MolaKule]

The "Density" spec determines if one oil is "heavier" than another because:

rho (Density) = mass/Volume; mass = rhoXVolume; Weight = massXgravity (g), therefore
Weight = rhoXVolumeXg

Density - Wikipedia

en.wikipedia.org

Difference Between Density & Mass

Mass and density are two commonly used physical properties of objects in physics that are very similar and share a close mathematical relationship. Mass and density should not be confused with weight.

sciencing.com

The proper term to use is "Kinematic Viscosity" in Centistokes (cSt) when comparing "Grades" of any lubricant. Each SAE Grade can have a Range of viscosity.

Viscosity Charts - Bob is the Oil Guy

Viscosities can be related horizontally only Viscosities based on 96 VI single grade oils. ISO are specified at 40°C AGMA are specified at 40°C SAE 75w, 80w, 85, 5w, & 10w specified at low temperature. Equivalent viscosities for 100° & 210°F are shown SAE 90 to 250 and 20 to 50 specified at...

bobistheoilguy.com

 

[SR5]

rho (Density) = mass/Volume ....

As a fellow physicist that is exactly where my mind first went. Don't even get me started over "lite" and "heavy" beers.

I've moved on though, a lesson learnt earlier in life, when explaining densities to a bartender ended up in very poor service for the rest on the night.

 

[Blake1107]

Thanks for the answers, all! Sorry I disappeared after posting. Opening weekend of rifle season in MO.

 

[ceecbtg]

Depending on what you mean with "heavy", about viscosity and additives a fast way to know the differences is the normative (API, ACEA, ILSAC). Here in EU we have many same SAE oils but from ACEA you can know easily as heavy or not it is, 5w30 C2 always has lower visco and additives than B4 or C3 etc. Car manufacturer spec is other fast way to know it.