Transmission Retarder OverTemp

[davidbrady]

How hot is too hot? I pulled this from an allison HD4000MH manual:

These temps define transmission overheating:

Sump fluid 121°C (250°F)
Converter out fluid to cooler 149°C (300°F)
Retarder out fluid to cooler 165°C (330°F)

A transmission tech at Prevost once told me my 2003 chassis H345 VIP will throw a transmission temp code at 150 degrees C. That must be the converter out fluid to cooler temp of 149 deg C spec-ed in the Allison manual. I think on my bus the retarder out of 165 deg C (330 deg F) is considered a transmission overheat event. I try to keep my retarder below 230 deg F, but I have gone as high as 250 deg F. At around 230 deg F the S60 cooling system fan comes on full speed. The Prevost Tech's also told me if your transmission fluid hits 300 deg F you need to dump it. But, Tom Johnson, the Allison fluid engineer who wrote the TES-295 spec of which Transynd belongs, says Transynd can take 330 deg F intermittently:

http://www.irv2.com/forums/f125/what-is-...60596.html