I'm a semi mechanic at UPS. The spotter trucks that all have an Allison automatic called for a 15W40 engine oil
up until about 12 years ago. Those transmissions hold up fine on it pulling semi trailers around the lot.
yes, but if you check the OP he has rotella 15w40 in the allison right now??
most sae 50W oils are allison approved including this one:
About Fleetrite Transmission Fluid
Navistar is excited to offer Fleetrite® synthetic automatic transmission fluid (ATF), a premium synthetic universal power shift and automatic transmission fluid that is TES-295approved for use in Allison transmissions. Fleetrite synthetic ATF is approved for Allison’s Extended Transmission Coverage Programs.
It does have the spin on filter.
It's very slow to shift when cold.
Then, again, everything is slow on this truck. Really like it. Rough ride, tough to steer, and brakes work great but you really have to stand on them.
It's a stinking blast to drive.
52-54 MPH tops.
For logistics purposes the US Army wanted to have a common engine and trans oil. The 15W40 was the diesel engine oil specified under MIL-L-2104D. So the trans was validated on both Dexron and engine oil. If you want better low temp performance, you could use a Dexron III spec oil or a 0W20 engine oil. 0W20 synthetic engine oil was the Army spec for engine and trans in arctic climate usage.