Chevron changed it's specs

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When did Chevron change its specs? The pour point of 5w-30 used to be -45f, now it is -33f. In my books it does not stand out as one of the best cold weather oil. What happened?
 

JonS

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I guess it is better. I seems weird that the pour point moves up, but it pumps better.
 
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The pour point of a conventional oil is generally determined by the wax content. A small amount of long chain paraffin molecules can form a gel-like network at low temperatures and trap the rest of the hydrocarbons. Pour point depressants act to inhibit the interaction between the wax molecules. The low temperature pumping properties of an oil, while limited by the pour point, are more of a function of the size distribution and shape of the majority of the hydrocarbon molecules as is the viscosity index. Chevron may now be using a more aggressive hydro-cracking method that improves the VI to the point where extensive wax isomerization (the iso-syn process) is no longer necessary. Just a guess.
 
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Sure. Waxes are long linear hydrocarbon chains. So a wax molecule that is say 24 carbons long is a pretty long molecule that can easily interact with other long molecules to form a network once the temperature gets low enough so that molecular motions doesn't pull everything apart. Chevron's iso-dewaxing procedure uses a chemical catalyst attached to a solid matrix that re-arranges the wax molecules into branched structures which have a smaller radius. So a 24 carbon linear molecule might be converted to a 24 carbon branched molecule. Since they have the same mass, but different structures, they are said to be isomers. The branched molecules don't form networks as easily as long linear molecules so you get a base stock with a low pour point. Severe hydrocracking treats a base stock with hydrogen at high temperature and pressure in the presence of different catalysts. Chemical bonds are saturated with hydrogen, broken, and often rearranged into branched structures. The resulting molecules have a much more uniform mass range than the feed stock and thus a higher VI. So, wax molecules are rearranged by hydrocracking as well. In fact, some of the best Group III base oils start out by treating "slack wax", which is essentially obtained by cooling down crude feed stock oil and allowing the wax to congeal.
 

JonS

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I think i am going to switch from Chevron to Mobil dino 5w-30. Mobil has cold crank of 5500 vs. 5700 of Chevron. Mobil pour point is -39f vs -33f for Chevron. Mobil is better in these two areas.
 
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Washington St.
quote:
Originally posted by Drstressor: ..... Chevron may now be using a more aggressive hydro-cracking method that improves the VI to the point where extensive wax isomerization (the iso-syn process) is no longer necessary. Just a guess.
Chevron has announced that they're going to produce more Group II+ base stock and less Group II at their Richmond refinery. The GR-II+ has the higher viscosity index/better cold crank numbers. I don't know if this means that Chevron is reformulating their own products or just producing more GR-II+ for sale to other customers. Note that Chevron describes Havoline as their "internal" customer, and Havoline, as well as other users, needs more GR-II+ base stock for more 5W-30 production. Ken
 
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JonS... do a search on my user name on the UOA board. I posted an analysis of 5W-30 Mobil, after a 3500 mile interval in a cold PA winter (down to 0 deg F). It did OK... nothing spectacular though.
 
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Gone
quote:
Originally posted by Drstressor: Sure. Waxes are long linear hydrocarbon chains. So a wax molecule that is say 24 carbons long is a pretty long molecule that can easily interact with other long molecules to form a network once the temperature gets low enough so that molecular motions doesn't pull everything apart. Chevron's iso-dewaxing procedure uses a chemical catalyst attached to a solid matrix that re-arranges the wax molecules into branched structures which have a smaller radius. So a 24 carbon linear molecule might be converted to a 24 carbon branched molecule. Since they have the same mass, but different structures, they are said to be isomers. The branched molecules don't form networks as easily as long linear molecules so you get a base stock with a low pour point. Severe hydrocracking treats a base stock with hydrogen at high temperature and pressure in the presence of different catalysts. Chemical bonds are saturated with hydrogen, broken, and often rearranged into branched structures. The resulting molecules have a much more uniform mass range than the feed stock and thus a higher VI. So, wax molecules are rearranged by hydrocracking as well. In fact, some of the best Group III base oils start out by treating "slack wax", which is essentially obtained by cooling down crude feed stock oil and allowing the wax to congeal.
...mmmmm, drstressor, could you explain everything after the part where you say, "Sure."
 
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