How Accurate Is Bob's Viscosity Chart?

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I was looking at Chevron's Supereme 5W30 conventional oil. St at 40*C = 64.8 According to the chart that would make this a 20W30! Am I doing something wrong? It should be betwen 28.8 and 35.2. I found the same trend when comparing other oils. The numbers at 100*C seem to match up.
 
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bobs chart is a 100VI striaght read across Multi vis oils with a higher than 100 Vi will not work on that chart. bruce
 
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I've seen that chart since forever, think it came out of an ASTM publication? It has probably been updated somewhere, it is only good for giving a general idea of the different grades imo....
 

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More help please.. What I need is a list/chart that shows what cST (both at 40 and 100) that an oil needs to fall within to be classified as a particulal weight/viscosity. Example: I know that to be a 30 weight the oil must have a cST between 9.30-12.49 cST @ 100 deg celsius. What about 20, 40, and 50? What about the first number @ 40? For example: to be an 0wX the cSt @ 40 needs to be between X and X cSt. The same for 5wX, 10wX etc. Can someone point me in the right direction? I want to know with great accuracy if a particular oil is on the "thin" or "thick" side.
 
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Just scroll down from that visc chart and you'll see the 100C visc's for 5 weight to 60 weight.
 

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I see that and thought my questions were answered when the chart was posted but if you take 40 weight, as an example, the chart showes between 10 and 20. The same for 50. The chart gives someone a general idea of the range, I'm looking for the EXACT range. I'm hoping someone has this information so an exact comparison to the nth degree can be performed.
 
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NO ..SCROLL DOWN to the OTHER CHART (NEXT CHART BELOW THAT ONE). It shows that a 40 weight falls between 12.5 and 16.29 CST @100C/212F Just in case ..go to the very bottom of the page and work up. First chart you see ...there you will most of what you seek. http://www.bobistheoilguy.com/visc.html
 

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Thanks for your help and patience Gary, your link answered part of my question. What about at 40*C? I'm understanding that chart to be for straight weight oils. Using Mobil 1 5w30 as an example, their data reads this oil as [email protected] 40cST. I have no idea if that is thick or thin for a 5wX oil. Is this information available?
 
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Well, OC, the chart is what an oil appears like in terms of visc at the respective temps. If you go to the various refiner sites they will list the 40C and 100C visc of their oils. M1 5w-30 is about 10CST thinner @ 40C then something like PZ HM dino. Depending on how you look at it, it thickened or thinned less over that temp span. It (M1) has a broader VI (viscosity index) in comparison. Sopus products (PZ, QS, Shell) XOM products except for Canadian Esso There's plenty more. Although there is more to it, essentially you take a 5CST oil and dope it with stuff (polymers that coil when cold and stretch out when hot) that is transparent at -30 (keep in mind that anything that is 5CST @ 100C is going to be motor honey @ -25) but gives the blend an appearance of a 30 weight @ 100C. So it's said that it's a 5 weight when cold and a 30 weight when hot. This is usually misunderstood as the stuff actually being thinner when you throw it in a freezer then it is when warm in your engine. What it means is that it thickens like a light Karo syrup and thins like a heavier one. It's still motor honey when stone cold. Like I said, there's more to it ..that's the Allan Visc by a Dummie version of the Cliff Notes.
 
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