What is 15w?

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By Detroit
I obtained a chart of 100C viscosities (cst) for the various SAE winter weight categories. It looks like this: 5W >3.8 10W > 4.1 15W > 5.6 20W > 5.6 25W > 9.3 30W > 9.3 So how does a 15W differe from a 20W? Why don't thy split the range (assuming 15W/20W run 5.6 to 9.29)? Is there a more subtle point that I am missing here?
 
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Ah thanks for the chart posting, unDummy. TallPaul - Need to look at it as whole, not just one column. Makes sense - that is the MINIMUM at 100°C - the low temp. properties are still controlled...by columnn 1 and 2.
 

Al

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So just to clarify TallPaul-The numbers that you have posted are really not what you are concerned about. A multiple viscosity oil like 10W-30 is required to be no more than 7000 cP at -25C . But on the other end the properties of the "30" part of the oil are required to be between 9.3 and 12.5 cSt(centistokes) at 100 C. Note that cP (centipoise) is used for low temperature viscosity designation and cSt (centistoke) used for higher temperature viscosity designation. [ October 30, 2003, 09:49 AM: Message edited by: Al ]
 

TallPaul

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Yeah I goofed. The 30 should not have a W. Also note that 0w and 5w have the same 100C min. I should have posted the whole table. The reason I am looking at the 100C viscosity of winter ratings is to compare the robustness of the base oil. And given the 100C column a 15W seems to be just as robust as a 20W. I understand that for 100C we are really interested in the back number (the 30 in a 1-0w30) but it is also true that the front (winter) number is the base oil and thus is your "if all else failed" bottom line. The back number is artifically attained by added polymers (Viscosity index improvers). Therefore, it would seem that a 10w30 would perform better than a 5w30, but a 20w40 would not necessarily perform better than a 15w40. So that is my drift, if you can follow.
 

Al

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quote:
Originally posted by TallPaul: Therefore, it would seem that a 10w30 would perform better than a 5w30, but a 20w40 would not necessarily perform better than a 15w40. So that is my drift, if you can follow.
By looking at these Ester and PAO properties and then comparing them to say Mobil 1 10W-30 you can get somewhat of a feel as to what is going on. Its apparant that M-1 10W-30 would need no VI or Pour Point depressants. I am assuming the mixture of the following: SpectraSyn 10 Estorex101 SpectraSynUltra (SuperSyn 150 Mobil 1 10W-30 Hope this helps
 
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My crude way of comparing robustness of the base oil is flash point, which correlates pretty well with oxidation and evaporation resistance. Taking Chevron Delo 400, a Group II+, for example. 10W-30 439F 15W-40 446F 20 451F 30 468F 40 489F 50 498F Note the almost linear progression up the scale.
 

TallPaul

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Thanks Al / Jimbo. You both make good points. I found some additional info in the Bosch Automotive Handbook (2nd ed, 1986) that compares the -18C (approx 0 F) viscosity of oils (instead of the usual low temp viscosity at different temps per weight. This one is apparent viscosity in mPa*s (min-max): 5w: max 1250 10w: 1250-2500 15w: 2500-5000 20w: 5000-10000 Note how each w increment shows a doubling from min to max, which indicates to me that a 20w could be 8 times more robust than a 5w.
 
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