Sump Oil Temps vs. Oil Viscosity

[THX1138]

I followed a link posted in a reply to a question I had about oil viscosity and proceeded to fall down a rabbit hole. I used Widman International's "Graph Your Oil" calculator to compare the viscosity vs. oil temp for the Xw30 oils I have commonly used. Widman states in an accompanying article that the SAE viscosities of the family of 30-weight oils ranges from 9.3 cSt to 12.5 cSt at 100C (212F). The resulting graphs showed the oils I've been using fall out of the target viscosity range at about 113C (235F). So I then researched sump oil temperatures and found a range from 20 degrees above coolant temp to as much as 1.2 to 1.4 times coolant temps. That could equate to 240 to 280 degrees F and put these 30-weight oils well beyond the target viscosity range.

If the 20F above coolant temp is accurate for sump oil temps then my oils are pretty much in the middle of the target viscosity range. If sumps oil temps are higher, then perhaps I need a heavier oil. I would appreciate anyone thoughts or explanations.

 

[zach1900]

10w30 and even 5w30 are so passe or so I'm told.

 

[gregk24]

Just use what the owners manual states.

 

[Garak]

Originally Posted By: THX1138
The resulting graphs showed the oils I've been using fall out of the target viscosity range at about 113C (235F).

SAE J300 doesn't let you play with temperature and say something is out of range because it's 113 C. If it's within range at 100 C, then it is the correct viscosity as claimed and labeled. It doesn't matter what happens at 113 C or 150 C or -273 C, as long as the KV values are correct for grade and HTHS falls where it should and the part before the "w" fits its specifications for CCS and MRV values.

 

[Quattro Pete]

Originally Posted By: THX1138
The resulting graphs showed the oils I've been using fall out of the target viscosity range at about 113C (235F).

The thing about the 100C kinematic viscosity values which determine what grade the oil is labeled as, is that they are measured at... wait for it... wait for it... 100 degrees Celsius. And that's it. No more, no less. It it expected for the viscosity to decrease above this temperature and increase below this temperature. Such are the laws of physics. Or is it chemistry?

Your engine manufacturer is aware of this and specifies oil grades accordingly, so no need to worry.

 

[Greasymechtech]

What engine/year/make/model/mods/PSI/weight/sump/oil?

Do nothing with a graph or calculator. Do something with your own accurate temperature and pressure gauges.

 

[ExMachina]

Essentially, engine designers simply specify a viscosity to be used based on the standard KV100 measure which puts an oil into say an SAE 30 category at 10 cSt measured at the standard 100 degC point. Its just a temperature picked out to be representative. Engine oil temperatures vary all over the place, from cold to hot, depending on the engine type, and designers know this & account for it.

Most engines are designed to have their oil at around 200 degF to 240 degF. Ford did a study a while back that had the ideal (lowest) oil chemical degradation occurring at 210 degF, or 99 degC, probably measured in the crank journal bearings. Of course oil temperature at the rings spikes to 350 degF easily, but in smaller volumes than the oil reaching the valvetrain, timing chain, & crankshaft, etc.
See Ford's:

from https://etda.libraries.psu.edu/paper/9507/5943

 

[3311]

For what it's worth. On my 04 below I recently checked the sump and oil filter temps with an IR gun. The sump/pan was 160f and the oil filter pre cooler was 220f.
This was with 95f+ ambient.

 

[PaulH]

whow, what you don't know.... I just do what it says in the owner's manuel and don't worry....

 

[THX1138]

Thanks for the replies. I was just trying to understand what I perceived to be an inconsistency in engine oil recommendations. Will do some more reading and consider the replies to my question. That's what BITOG is for after all.