Originally Posted by Y_K
Originally Posted by ka9mnx
I couldn't find the article I was referring to but here are a few (of many) good reads from Machinery Lubrication:
https://www.machinerylubrication.com/Read/29954/synthetic-gear-oil
https://www.machinerylubrication.com/Read/167/synthetic-gear-oil
Thank you. According to the articles, even a lowly mineral oil should be good for 200k miles in old geezer mode.
==============================
Synthetic oils have better resistance to aging and high temperatures and a longer service life than mineral oils. Depending on the base oil (SHC or PAG), the oil change intervals may be three to five times longer at the same operating temperature.
Approximate oil change intervals of gear oils
at an operating temperature of 176°F (80°C) are:
Mineral oil: 5,000 operating hours
SHC oil: 15,000 operating hours (extension factor 3)
PAG oil: 25,000 operating hours (extension factor 5)
Synthetic oils have a lower friction coefficient than mineral oils in a gearbox and a more favorable viscosity-temperature relationship. This generally permits the use of synthetics at lower viscosity grades and also offers the possibility of reduced oil temperature during operation. In such cases, the life extension factors for oil change intervals of synthetic oils are longer than the values stated above, which refer to identical oil temperature.
The following comparison of test results illustrates this advantage. Three lubricants were tested in a splash lubricated worm gear test rig.
The test records show the following oil sump temperatures after 300 operating hours:
Mineral oil: 230°F (110°C)
SHC: 194°F (90°C)
PAG: 167°F (75°C)
The life extension factors of synthetic oils as compared to mineral oil are as follows:
Mineral oil = 1
SHC = 9.5 times longer
PAG = 31 times longer
Does it occur to us that :
Operating viscoisities of PAG >> is higher than that of SHC, >>>> which in turn is higher than that of Mineral oil, hence leading to
Operating temperatures PAG whilst all these 3 oils are of
similar viscosity grades at KV@40*C in the context of industrial gear oils , which the article fails to highlight or not expressed.
It's the operating viscosities that matters, not (base) oil groups per se.
It's confusing, I know.
Edit:Mineral gear oil operating at 110*C is simply an incorrect viscosity grade selection by owner , other than gearbox design dificiency.