Should I change?

[Patman]

quote:

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Originally posted by JonS:
Patman,

The vis of 9.8 vs. 11.5 is at 212 degrees. I used to watch this also and figured, my oil is not going tobe at 212 all the time. It might be at 180 one day then 250 the next , depending on how you drive ect. Plus, this is just an average from a sample taken. One guy at a refinery i talked to went thru some of a batch he was testing. Some was at 10.2, some was at 11.7. These numbers on the spec sheets are averages and change (i've heard) dramatically with a few degrees either way. So, your Max- Life at 250 might be "thinner" than Mobil1 at 250 because of the viscosity index is higher.

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I've been thinking about this a lot today and it really bothers me. Are all oil companies like this, or do you think it might have just been at that one refinery? I find it hard to accept that they can't make their batches of oil more uniform. It also makes it harder to determine if your oil has thinned or thickened through analysis, because you might not know exactly where it started at! I also wonder if the other factors of an oil vary this wildly? In other words, if they claim the oil has a pour point of -40F could it vary as much as ten degrees either way? If so, an oil that might be marginally safe to run in your winter climate might just end up with one batch being safe and the other being a bit risky. Not good!

What would make an oil vary so much in viscosity from one being at 10.2 and one at 11.7? Would they add different amounts of VII? Or is it the base oil which determines this variance? And if so, wouldn't a synthetic be subject to less production tolerance since they are "custom making" the base oil? (I'm talking real synthetics here, not the group 3 pretenders)

 

[UncleS2]

Petrolem comes from the ground as-is, and there are differences in oils from different oilfields. That alone may be enough to account for the fact that some specs are given in ranges instead of a single figure.

 

[ZR2RANDO]

Stuart,
petroleum comes from the ground, as is, and is then HEAVILY processed...the hydrocracking process is an old process, it did not get famous just because the API finally got to the SL classification of oils.
Specs are in ranges because of manufacturing abilities, costs and minimum requirements, not because of raw materials. If specs were made to an absolute value we would be paying top dollar so the mfgrs could make exact value specifications which would effectively gain nothing.

 

[widman]

The range is partly from variations in the base oil and partially due to the lack of need for it to be exact and still be within what the API thinks is needed.
Remember that these viscosities are only valid for new oil. It will begin to change with the first few miles, depending on temperature, loads, the quality of the base oil, and the grade of VI improver used. Carefull guesswork goes into matching those elements so that as the oil thickens from oxidation the VI improvers shear, leaving you with an oil that still meets the API specs

 

[ZR2RANDO]

Variations in the raw materials does not dictate what the API sets as required standards for classification/wt of motor oil. They do however pose a challenge to the manufacturer to make a consistant product within the specs that the API sets though. The API sets minimum requirements for the physical properties and the allowable deviation from those values (if that deviation was too small the cost would go WAYYY up). The manufacturer does the best he can to minimize variation of inputs (raw materials) so that process control avoids any extreme corrections in the overall process flow....ok now can I be a lawyer? can I?
Seriously, the API does not care about the raw material fluctuations or any other problem the manufacturer has, they just set the standards that the boss is setting for them....wait a second, maybe the manufacturers are the boss???

Have a great weekend folks!
Rando