I wish I knew this thread was open when it was active. It's a good subject.Molakule, we had some issues a few years ago with ISO460 gear oils rapidly becoming 200(ish) in service. The manufacturer denied having Viscosity Modifiers in their ISO grades, pointing to the 98 VI...but within 3 months, no changes at our end on multiple pieces of equipment, the oil stopped breaking...three years later, it was back again...evidence of PIB (or similar thickeners)
Interesting I have done exact same thing with h-300 as well as PAO 100.I wish I knew this thread was open when it was active. It's a good subject.
Several years ago I was looking for low cost synthetic fluids or VMs (thickeners) for an ISO 680 gear oil. I formulated using a base fluid of 12% Indopol H300 (polybutene; KV100=605-655; VI=173) and bright stock (GI mineral oil; KV40=480). This would have yielded a VI of about 98-102. Long story short, I put the oil into a planetary swing transmission of an electric rope mining shovel, a high shear application. The oil began to loose viscosity within a few days and at 14 days it was down to about 525 KV40. I repeated this another time with the same result. Polybutene/PIB does not appear to be shear stable in geared system.
You can identify polybutene by infrared spectroscopy. Further, I wouldn't be surprised to see the VI drop as viscosity drops.
VMs, especially the VII type, are task specific. In other words, a VII developed for gears is stable in a geared system but not in an engine. Powersports engine oils with shared compartments are extremely damaging to many VIIs. A VII may be fine in separate compartments but when exposed to gears or a wet clutch loss viscosity immediately.