viscosity change over time/temp

KiA · Jun 5, 2004

i'm trying to imagine what happens to oil viscosity over time as the car warm up to temp. corrent me if i'm wrong:

1) with a multi grade like 10w-30, it acts as lower viscosity at lower temps, and it moves up to 30 grade.
2) then as it heats up more it thins out
3) depending on the generated heat, the viscosity probably goes up and down within the grade limit.

i made a graph to illustrate my view:

let's say ambient temperature is 40F.
what do you think?

XS650 · Jun 5, 2004

quote:

Originally posted by KiA:
i'm trying to imagine what happens to oil viscosity over time as the car warm up to temp. corrent me if i'm wrong:

If you plot temperature vs viscosity on an ASTM D341 standard temperature vs viscosity chart, you will get nearly a straight line for straight viscosities of multi grades.

The difference being that the line for the multi grades will be flatter because they don't thin as rapidly as the oil heats up.

KiA · Jun 5, 2004

i found this:

[ June 06, 2004, 04:37 AM: Message edited by: KiA ]

FowVay · Jun 5, 2004

I plotted my own graph of three different viscosities - 5w/10w/15w-40 Amsoil - just to get a idea of the actual difference in these products.
I plotted at 10ºC intervals starting at 0º and working up to 130ºC. My finding was that none of the oils followed a linear scale like the one shown above. Of course, my graduations were much more numerous and on a much smaller viscosity and temperature table than the one published above. This would definitely skew the averages in this case.

The cold temp property for each oil started at a different point and the high temp property ended at nearly the same point but the rate at which they achieved this high temp point was considerably different between each grade.

I also did this same plot using 0W/5W/10W-30 and I was amazed at the actual different in each of these oils with regards to their rate of flow change. My main concern was with temperatures starting in the 10ºC range since that is more in tune with my morning starting temperature.

I used this web page to give me the exact viscosity at a specific temperature:

http://www.geocities.com/CapeCanaveral/3655/VI.html

[ June 06, 2004, 06:16 AM: Message edited by: FowVay ]

TallPaul · Jun 5, 2004

KiA: Your plot looks very realistic but only if the x axis is time. Adding temp to the x axis is throwing folks off because the temp is not scaled or linear on the X axis with your graph. In the first inch or so it has the linear form of a evenly warming oil, but after that temp is fluctuating within the operating temp range and that is why the line levels and is squiggly. Nice work.

Edit: Actually, temp is probably near linear for the Y axis since viscosity varys closely with temp.

Edit 2: The viscosity on the Y axis should vary from maybe 6000 cSt at the bottom to about 10 to 12 at the top since the oil is thinning.

[ June 06, 2004, 08:45 AM: Message edited by: TallPaul ]

KiA · Jun 6, 2004

quote:

http://www.geocities.com/CapeCanaveral/3655/VI.html

i did find that page. i was short of plotting my own graph before i retired to bed. i'll try that in excel.

quote:

KiA: Your plot looks very realistic but only if the x axis is time.

i changed the graph to say only time.

quote:

The viscosity on the Y axis should vary from maybe 6000 cSt at the bottom to about 10 to 12 at the top since the oil is thinning.

i think my trouble is with understanding multi grade oil. doesn't it change from a 10w to 30 as it heats up? to me that sounds like it starts thinner (due to lower visocisty of 10w) and gets thicker until it reaches range of 30 grade oil.

unDummy · Jun 6, 2004

No Kia, it doesn't change from a 10w to 30 as it heats up. You fell for the bottle label viscosity misnomer.

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=1;t=006752

jetfixer · Jun 6, 2004

The way I understand it the oil thins out as it gets hot, so a 10 Winter is really like a 100 wt oil lets say.This 100wt can flow and be pumped down to -15F for example.As this oil heats up it thins so at 180F a 10w-30 is really a 40wt untill it reaches 212F were it will be a 30wt.Once the oil temp passes 212F it keeps thinning so the oil will flow like a 20wt.

Bill Morris · Jun 6, 2004

So what happens to say a hd straight 30wt oil. On some engines the manual states to use a straight 30wt.

jetfixer · Jun 6, 2004

A mono grade 30WT stays a 30WT thru any temp.This oil is good in a hot climate that stays above 40F.

JohnnyG · Jun 6, 2004

You guys aren't quite getting it right yet.

A 30 weight (straight 30) still thins out as it gets hot. It does not "stay at a 30wt", but thins out the same as a 30wt multi-weight would.

A multi weight, lets use 10W-30 as an example, has the viscosity that a 10W would at low temps, keep in mind that a straight 10W would thicken up to something around a straight 30w or higher(at normal temp) would, when it is cold.
The high number (30) has the same reaction as the oil is heated up....it thins out. BUT, it only thins out to about the same as a staight 30W would when raised to that temp.

Dominic · Jun 6, 2004

Let's make it simple so earlier posts can be deciphered:

Rules of All Oil:
1. They're thicker when cold than when hot
2. Monograde oils are thicker than multigrade oils at low temperatures.
3. a Multigrade oil's final number (20/30/40/50) means at 100C, an XW-30 is roughly the same as SAE30 monograde in terms of flow and viscosity.
4. A multigrade oil's first number (5W;10W-X) does not correspond to any SAE monograde weight, but is instead a Winter Reference Number.

That should clear some things up

can we post this on the frontpage?

KiA · Jun 6, 2004

ok, i think i understand now.

unDummy, that thread helped quite a bit.

question:

quote:

A multigrade oil's first number (5W;10W-X) does not correspond to any SAE monograde weight, but is instead a Winter Reference Number.

so, if i look at the viscosity chart:

i can't say an SAE 10w (say 25 cSt) @ 40c is similar to an SAE 60 (22-26 cSt) @ 100c? (this is similar to what jetfixer mentioned)

[EDIT> i've changed my initial graph to what i understand now.]

[ June 07, 2004, 02:40 AM: Message edited by: KiA ]

TallPaul · Jun 6, 2004

quote:

Originally posted by KiA:
i can't say an SAE 10w (say 25 cSt) @ 40c is similar to an SAE 60 (22-26 cSt) @ 100c?

The referenced 10w oil would have the same viscosity at 40C as the referenced 60 wt has at 100C.

On the graph, you need to have increasing temp on the Y axis. The "100C" at the top implies that all the Y axis is at 100C, but I don't think you meant that. Going from about 25 cst to 11 cst would likely be a range of 20C ambient up to operating temp of the oil (100C?).

Cary · Jun 7, 2004

If someone can host them, I have the actual PDF files of Mobil 1 and Mobil mineral oils showing their viscosity v. temp. They were given to me by another list member last year.

Cary

KiA · Jun 7, 2004

i plotted zoomzoom's data (note that Y-axis is Log scale):

zoomzoom · Jun 7, 2004

I calculated Vis vs Temp for M1 0W-40, GC and M1 10W-30...Pretty interesting to see how it changes with temp:

TEMP(C)/M1 0W-40/GC 0W-30/M1 10W-30

-20/2661.5/2609.0/3424.8
-10/1197.8/1127.1/1332.9
0/599.3/546.6/595.7
10/327.6/291.8/298.3
20/192.9/168.8/164.1
30/121.0/104.4/97.6
40/80.0/68.4/62.0
50/55.4/47.0/41.6
60/39.8/33.7/29.2
70/29.7/25.0/21.4
80/22.7/19.1/16.1
90/17.8/15.0/12.5
100/14.3/12.0/10.0
110/11.7/9.8/8.1
120/9.8/8.2/6.7
130/8.2/6.9/5.7
140/7.0/5.9/4.9
150/6.1/5.1/4.2

I used this caluclator:
http://www.geocities.com/CapeCanaveral/3655/VI.html

zoomzoom · Jun 7, 2004

I always wondered what are the temperatures that oil experiences on its cycle trough engine?

KiA · Jun 8, 2004

quote:

I always wondered what are the temperatures that oil experiences on its cycle trough engine?

someone with an oil temperature gauge could help. although from what i've seen most people that install the gauge have little clue about its practicality.

here are the PDF files that Cary mentioned:

Synthetic [0w-30, 5w-30, 10w-30, 15w-50], 175KB

Mineral [5w-30, 10w-30, 10w-40, 20w-50], 161KB

EPA GF3 approval letter concerning 5w-20, 198KB

[ June 08, 2004, 04:06 PM: Message edited by: KiA ]

DEWFPO · Jun 8, 2004

Based on KIA's graph .... does that mean that a given oil at 0C or 32 F has about 70 times the viscosity as that same oil at 100C or 212F?

70 times?

I hope I'm wrong.....

DEWFPO

viscosity change over time/temp

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