Viscosity temperature plots for oils

[RalphVa]

If you want to see how oil viscosity changes with temperature, here's a good site: C:\Users\user\Documents\Car Stuff\Viscosity_temperature_oil_plots.png

Below is a plot when I put in -40 as the minimum temperature (-40 is same in F or C).

At 1,000,000 Cs, no oil will flow. These will all flow at -40, but the oil pump will have trouble picking up suction on any but the very lightest short before many seconds or running. In the meantime, the upper valve train can go totally dry and actually start smoking. Imperial Oil, Exxon's oil research arm prior to their moving it all to Baton Rouge, did research on this many years back whereby they started a Chrysler 4 cylinder with transparent valve cover in a -40 room using various oils. There was quite a long delay in getting oil flow from all oils except a 0wxx oil. No dino oil could be made at that time to 0wxx specs and still meet volatility specs, particularly the stringent Noack one being tested at that time.

Many oil pumps also will require more energy to pump the oil if the oil is very viscous. Most oil pumps are designed to pump too much oil, with the excess going on pressure bypass back to the sump. This pumping energy, especially on startup, is mainly what can be reduced by use of synthetic oil. However, synthetic also seems to be more slippery (probably due to much fewer additives that may not be as "oil" like) at operating temperature and increases hp there. This is the main reason why car racers use synthetic. Of course, it will not break down so readily under the rigours of racing like dino oil with lots of additives.

Ralph

 

[RalphVa]

Oil follows a straight line if plotted on special loglog vs. 1/T paper available from the ASTM. Too bad they cannot show this. Guess the plain cS vs. temperature plot is all they could put on line.

Ralph

 

[SPYDERLK]

If you want to see how oil viscosity changes with temperature, here's a good site: C:\Users\user\Documents\Car Stuff\Viscosity_temperature_oil_plots.png

Below is a plot when I put in -40 as the minimum temperature (-40 is same in F or C).

At 1,000,000 Cs, no oil will flow. These will all flow at -40, but the oil pump will have trouble picking up suction on any but the very lightest short before many seconds or running. In the meantime, the upper valve train can go totally dry and actually start smoking. Imperial Oil, Exxon's oil research arm prior to their moving it all to Baton Rouge, did research on this many years back whereby they started a Chrysler 4 cylinder with transparent valve cover in a -40 room using various oils. There was quite a long delay in getting oil flow from all oils except a 0wxx oil. No dino oil could be made at that time to 0wxx specs and still meet volatility specs, particularly the stringent Noack one being tested at that time.

Many oil pumps also will require more energy to pump the oil if the oil is very viscous. Most oil pumps are designed to pump too much oil, with the excess going on pressure bypass back to the sump. This pumping energy, especially on startup, is mainly what can be reduced by use of synthetic oil. However, synthetic also seems to be more slippery (probably due to much fewer additives that may not be as "oil" like) at operating temperature and increases hp there. This is the main reason why car racers use synthetic. Of course, it will not break down so readily under the rigours of racing like dino oil with lots of additives.

Ralph

Yipes! ... A LOT of activity very near freezing. My engines have seen the last 20W ever.
,,,Thanks for posting.
larry

 

[DFB]

Yes sir and that might also just explain why the oil pumped right out the pushrod/lifter seals when I tried starting my Harley big twin that was stored outdoors in the wintertime some many years ago :laughing:

 

[RalphVa]

Out of curiosity, I did some internet looking into the Pierburg (think this is how it is spelled) oil pumps that most engines have. There was some information that showed their pumping rate is GREATLY reduced at lower and lower temperatures, even temps not so low.

It's easy to see how 40w oil shown in the plot at around 500,000 cS wouldn't pump too well. Whether the pump will pump it all depends on it getting through the suction screen and short length of suction pipe to the pump. At elevated cS values, it just won't flow or flows like molasses.

I was kinda disappointed that 0w20 and 5w30 oils didn't intersect somewhere at elevated temperatures. None of the ones shown do. If you plotted some regular 30w or 40w oils, they'd likely intersect at elevated temperatures, e.g. because they thin out so much at higher temps.

Ralph

 

[SPYDERLK]

Different weight oils, while adhering to their weight spec should never intersect if there is any sense to the world. The "intersection" is apparent only - due to the gross viscosity scale on the graph. ... Right?
larry

 

[DEWFPO]

Back in the day I had a '68 Ford Torino (302ci 2-bbl) that I had installed a mechanical oil pressure gauge in and was running dino 10W30 motor oil in. On cold mornings (below freezing), the oil pressure would take a while to register on the gauge even thought the oil pressure light was out on the dash. Then the oil pressure would start to drop down towards the bottom of the scale before it started to move up again and stay up. The first time I saw that it startled me but then I got used to it. It never seemed to hurt the engine.

DEWFPO