Originally Posted By: AirgunSavant
Special additives to reduce oil gelling........
Use 0w20 and move on was not answering the question........
No objection either and I thanked him.
"Gelling" and "Low Temperature Gelling" aren't anything to do with sludging, and certainly not that 0W or 5W flow better at 0F (you can't make that distinction, they are the tests at -30 and -40Fs to differentiate them.
Gelling in oils is akin to the same problem in diesels, but more specific and much worse.
During the 80s there were a spate of engine failures at apparently sane temperatures for the oils of the day and they found that at specific cooling rates, wax crystal formation was promoted, causing the oils to fail to flow up the pickup tube...it's a part of the reason for the "don't store oil in a cold garage" story.
The oil then developed a "memory", and it's "W" characteristics were compromised severely at even "normal" temperatures, and the memory could not be reset until the oil was heated to 80C.
Some previous discussions.
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4019886/Re:_low-temperature_oil_gellin
https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3999169
So...WAG hat on now.
Maybe they are starting to notice that in some locations and duty cycles that the hybrids aren't getting the oil warm enough to reset the memory, and over time are developing waxy gels, accumulating in service...going to a 0W whch SHOULD have less waxy constituents, and probably more defensive additives would help.
Another great paper by Selby, one of the best researchers IMO on low and high temperature rheology
chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/http://www.savantgroup.com/media/SBT-SAE-922287.pdf
If he'd have had his way, the "W" ratings would have looked VERY different.
disclaimer : this, as always is my presentation of somebody else's work, using charts cherrypicked from papers that may or may not be as fresh as yesterday's bread.