[Railcarmover]

It would be interesting to see what the viscosity of the off the shelf 600w is at operating temperature.I do know foaming in an issue.STP and other additives are not tested for pressure,in other words,even though its thick it might not handle the tooth on tooth contact pressure of engaged gears under load,possibly ending up with accelerated wear.That's where the API designation is critical,it tells you,by testing, how the oil handles the actual condition its under,way more scientific than looking at it and approving it by how thick it is.