Generally speaking do multi-grade motor oils rely on one or the other or both?
What are the advantages and disadvantages of both?
What are the advantages and disadvantages of both?
Pour Point Depressants vs Viscosity Index Improvers
- Thread starter BMWTurboDzl
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PPDs are predominantly used with Group III/III+ base oils with synthetic oil and not so much with GTL. Their use largely depends on the quality of the Group III/III+ base oil. You can have a thin, average-quality Group III base oil that will form crystals earlier than a better quality one, so you must use PPDs. Then you must also use more VII to get to the operating viscosity you want. It's not an ideal situation. An example of this is Castrol EDGE Extended Performance 0w-20. It freezes solid just before or around -40C, is made with thin base oils, and uses polymers to reach around 8.6 cSt @ 100C.
Ideally, a good quality base oil should be used and as few PPDs as possible. High-quality VII (e.g., star polymers) can help a thin base oil achieve higher operating viscosity and stay there without shearing much.
At least that's my take on the issue.
Ideally, a good quality base oil should be used and as few PPDs as possible. High-quality VII (e.g., star polymers) can help a thin base oil achieve higher operating viscosity and stay there without shearing much.
At least that's my take on the issue.
OVERKILL
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All base oils that aren't PAO or Group V (and nobody uses esters in the quantity for that to matter) require PPD's for their cold temperature performance, because the hydrocracking process does not remove all the slack wax. When the temperature drops, at some point, you get wax crystal formation and that's when the oil begins to rapidly, and massively, increase in viscosity. PPD's work to push down the temperature at which that process takes place so that the oil can meet the intended Winter rating.
GTL bases have less wax in them than most other Group III's, so they require comparatively less PPD support. PPD's may also be used in PAO-based lubes to deal with the same phenomenon in the carrier oils. There are some examples in the Mobil blending guide that show PPD's, some that don't, like this for example:
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