Some years ago I stumbled across an interesting experiment/study on oil analysis between oil changes in motorcycle engines. One of the points that was exposed is that our transmissions are lubed by the engine crankcase oil. The constant gear meshing applied far more shear forces to the oil than when oil used solely in engine crankcases as is common in automotive uses.
The report found that multi viscosity oil blends reverted to base stock viscosity much sooner in motorcycles. The explanation is that when the oil is formulated, additives are included to make the base stock behave as thicker oil (higher shear strength) when hot by these additives. They explained that part of the additive package introduced long chain molecules that shrunk when cold and extended when hot. The reaction to temperature is what gave the oil the higher viscosity behavior when hot. The transmission's gears chop up the long chain additive molecules, with the result that the oil looses its viscosity modification rating, which reduces the shear strength of the oil during progressive use.
IIRC:
The study had oil analysis samples at 200 mile intervals. They used a liquid cooled engine, in order give the oil a more stable oil temp throughout its use. (This is something air cooled engines do not have the luxury of providing, and excessive heat is well known to reduce oil effectiveness damaging both the base stock and oil additive package molecules.)
Anyway the study showed a sharp decline in long chain molecules at around 1000 miles of use. Meaning a 10W-40 oil was effectively a 10W-30 oil at 1000 miles. This tapered down to 10W-15 at about 1500 miles. By 2000 miles the oil analysis showed that the oil has lost all of it's multivis properties.
Bear in mind, that study was at least 15 maybe 20 years old by now. Perhaps they have more robust long chain molecules in today's additive packages. Oil formulation details are quite secretive by oil companies, relying far more on marketing claims of "better" and "testimonial innuendos" than any objective performance data or chemistry specifics.
However, I found it curious to note oil behavior in my CB550's. The metric noted by me was effectiveness of the clutch and it's tendency to begin dragging at right around 1000 miles (varies with seasonal temps), and getting clunky shifts, harder to select neutral, from that point on, towards my 1500 miles oil change interval. The clutch drag and clunky shifting went away very shortly if not immediately after the oil change.
Perhaps you'll find interest in this, yet another, oil thread discussion.
That would be an interesting test to replicate with modern oils
I just sent Blackstone a request for a test kit. I’m at about 1k on rotella t6 15w40 right now
T6 load carrying capacity is a little lower than the Rotella T4 conventional.
The T6 failure temperature is 260* whereas the T4’s is 250*…fwiw….
And as 2 tired posted, I was taught the same that conventional multigrades degrade quickly with heat and contamination.
The last “conventional oil” training I attended was 10+ years ago too. My recollection is very similar to 2tireds. However the class attendants were taught the base stock oil weight chosen for the premium multi grade oils was the most important part of the formulation for the location used (design temperature). The 10w-40 multi grade oil was used as the example.
If the particular batch of premium multi grade oil (non discounted oil) was destined to be sold in the North, the base stock oil selected may be a 20weight. While relying on the formulation of the needed viscosity index improvers to lower the 20weight base stock tomaeasy flowing 10winter. And viscosity modifiers to raise the 20weight base stock to a 40 weight at operating temp.
While the batch of premium multi grade destined to the heartland may start life with a 25 weight base stock. While relying on the same viscosity improvers/modifiers to do the same as above.The manufacturer knowing when the additives wore out it would return near its base stock weight.
And finally the premium batch headed to Texas and New Mexico may start with base stocks at 30 or 35weight depending on the time of year it was formulated and predicted to be sold. (Summer or Winter). And the needed viscosity improvers/ modifiers added etc.
So it’s obvious the oil manufacturers know the additive package will soon break down and selects the base stock most appropriate for the area and temperature for the base stock oil. So that brings up the discounted oil 😜. Guess what they use to empty their odd end lots….😳 I Remember one of the viscosity index improver/modifiers is way more expensive. I’m not sure whether it’s the improver(cold) or the modifier (hot) that makes the base stock act as a winter oil or the one that makes act as a heavier weight at operating temp…Guess which one your getting with the cheaper close out oil….😁
