how does viscosity changes as Temp goes up?

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I know it thins out. I wanted to know at what rate does it thin out. Is it a linear rate? I am using AMSOIL so it should be fine. Normal high way driving is around 110 so it is not too high
 

MolaKule

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It varies logarithymically. You'd have to plot it and then take the derivative, which would be the rate (slope) of oil thinning as temps rise.
 
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From what I have read. A ball park number is it changes one grade level for every 23 deg. F. In the 190 - 260 deg. F range. Something to think about for the ones here running 5w 20 on a hot summer day.
 
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I have seen some good data on this here. Do a search. The base stocks should give a straight line with the log of the viscosity decreasing when plotted against the reciprocal of the absolute temperature. The synthetics naturally decline at a slower rate than dino. Viscosity index improvers, VII, are added to oils, the reducing the effect of temperature, at least over the range from a cold engine to a warm one. That can lead to some strange curves.
 
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quote:
Originally posted by Hirev: Something to think about for the ones here running 5w 20 on a hot summer day.
I have yet to see anyone state what kind of oil pressure they get with this 5w20 stuff. I'd think they would need a high volume pump to keep it from leaking out the bearings too quickly. [crushedcar] Sorry. I know about all the good UOAs, but I can't help ripping on the 5w20. Just in fun [Wink] , but I won't use it.
 

kickster

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My vw oil temp is around 80C to 90c on short city trips. If I go on Highway for more than 10 minutes it goes to 100 C. After 10 min it slowly goes to 110c @ 100 KM/h if I go 130KM/h the temp climbs to 115 to 118 c. Once I did a 210Km/h run for 2 min and oil went up to 125c Another time my coolant hose blow up and I drove it with no water for 5 min, oil temp went up to 150c which is the maximum on my gauge. How does oil viscosity changes as temp goes up, I have seen the numbers @100 but I dont know how it changes as temp goes up slightly higher than 100.
 
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I think viscosity takes a dump as temp gets that high. If we use the HT/HS as an indicator of the 150C viscosity (although HT/HS may not be a good indicator of overall viscosity) we see quite a drop. Overall viscosity may not be so low as HT/HS is meant to simulate viscosity in under pressure in the bearings and a lot of your oil is circulating and in the pan. I hear it is normal for oil to get hot at high speed operation and run cooler at idle. In your case consider an oil cooler, bigger sump capacity, true synthetic oil.
 
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Here is example: TEMP * M1 0W-40 * GC 0W-30 * M1 10W-30 * M1 0W-20 -20 * 2661.5 * 2609.0 * 3424.8 * 1712.7 -10 * 1197.8 * 1127.1 * 1332.9 * 730.8 0 * 599.3 * 546.6 * 595.7 * 352.8 10 * 327.6 * 291.8 * 298.3 * 188.5 20 * 192.9 * 168.8 * 164.1 * 109.5 30 * 121.0 * 104.4 * 97.6 * 68.3 40 * 80.0 * 68.4 * 62.0 * 45.1 50 * 55.4 * 47.0 * 41.6 * 31.3 60 * 39.8 * 33.7 * 29.2 * 22.6 70 * 29.7 * 25.0 * 21.4 * 17.0 80 * 22.7 * 19.1 * 16.1 * 13.1 90 * 17.8 * 15.0 * 12.5 * 10.4 100 * 14.3 * 12.0 * 10.0 * 8.4 110 * 11.7 * 9.8 * 8.1 * 6.9 120 * 9.8 * 8.2 * 6.7 * 5.8 130 * 8.2 * 6.9 * 5.7 * 5.0 140 * 7.0 * 5.9 * 4.9 * 4.3 150 * 6.1 * 5.1 * 4.2 * 3.7 [ July 22, 2004, 11:18 AM: Message edited by: zoomzoom ]
 
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While we are at it, I have one question. It has been said on this board that using lighter oil like M1 0W-20 will make engine run cooler. Has anyone been able to verify this by actually noting the difference in their oil temperature between 30/40wt and 20wt given the same conditions? For example what was the oil temperature in: 1. Regular city driving 2. Highway driving 3. High-speed highway driving(like 80 mph+) I guess if the car run cool enough then 20wt would behave like 30wt? I whish I had oil temp gauge on my car [Frown]
 
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