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https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2048544
Notice interesting comment about TBN just a few down from top …
Notice interesting comment about TBN just a few down from top …
Viscosity thickening, long drain
- Thread starter pitzel
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Dropped the pan and put the old oil back in. That's like apocalyptic Mad Max or zombie shtf scenario level conservation of resources. But then again I work on cars every day that are sludgeballs by the time the customer "didn't make it back in for service because X trivial reason" for 20k miles. Accidental extended drains. Last one had 18k-ish.
25k miles on HDD 5W-30, similar to XD-3:
https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/2726844/1
Thickened to a 40-weight.
https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/2726844/1
Thickened to a 40-weight.
Originally Posted By: pitzel
"ASTM STP621_S4 Cold Starting and Oil Pumpability —An Evaluation of New and Used Oils in Gasoline Engines", but its very old (~1980) and implies that a 'used' 10W-30 becomes a 20W-40 in their case. Not sure such logic is applicable to modern synthetics though which don't rely upon viscosity modifiers.
From recollected reading (I havn't read up on this specially, so my memory may be at fault) viscosity gain is supposed to be mostly due to oxidation and polymerisation of the base oil, with a corresponding rise in AN due to the formation of organic acids. Viscosity modifier breakdown, typically due to shear, would be expected to reduce viscosity.
Synthetic base oils would be expected to have ralatively high oxidative stability but this is not always reflected in the performance of finished oils. For example, in this study:
COMPOSITION AND OXIDATION STABILITY OF SAE 5W-40 ENGINE OILS
the two oils showing the lowest oxidative stability were both full synthetics.
Many of the oxidation processes are self-sustaining "cascade" chain reactions, so once the anti-oxidants are depleted, the oil may "go critical" and deteriorate quite quickly. Better keep a close eye on it.
Off course its up to you, but if you aren't monitoring this in a way that would produce data as well as give you warning, its value as an experiment, even just to satisfy your own curiosity, may not justify the risk of damage. Depends how invested you are in the vehicle.
"ASTM STP621_S4 Cold Starting and Oil Pumpability —An Evaluation of New and Used Oils in Gasoline Engines", but its very old (~1980) and implies that a 'used' 10W-30 becomes a 20W-40 in their case. Not sure such logic is applicable to modern synthetics though which don't rely upon viscosity modifiers.
From recollected reading (I havn't read up on this specially, so my memory may be at fault) viscosity gain is supposed to be mostly due to oxidation and polymerisation of the base oil, with a corresponding rise in AN due to the formation of organic acids. Viscosity modifier breakdown, typically due to shear, would be expected to reduce viscosity.
Synthetic base oils would be expected to have ralatively high oxidative stability but this is not always reflected in the performance of finished oils. For example, in this study:
COMPOSITION AND OXIDATION STABILITY OF SAE 5W-40 ENGINE OILS
the two oils showing the lowest oxidative stability were both full synthetics.
Many of the oxidation processes are self-sustaining "cascade" chain reactions, so once the anti-oxidants are depleted, the oil may "go critical" and deteriorate quite quickly. Better keep a close eye on it.
Off course its up to you, but if you aren't monitoring this in a way that would produce data as well as give you warning, its value as an experiment, even just to satisfy your own curiosity, may not justify the risk of damage. Depends how invested you are in the vehicle.
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