Allison Retarder Temperatures

A few years ago at an FMCA Seminar on Allison, and in the Q&A session, I learned following

• Allison provides two temperature outputs, one in the sump, the other in the retarder section. Foretravel uses the sump sender, perhaps because the temperature swings on the retarder are much faster and higher, and could cause unnecessary alarm and/or concern.
• At about 300 degrees in the retarder, the software starts “load shedding”, and at about 330 degrees, the “shedding” is close to 100%, meaning the retarder has shut down “retarding”.
• The Senior Allison Rep advised that 250 degrees in the sump is equivalent to 300 degrees in the retarder section.

My conclusion and current practice is to use 200 degrees (sump) as a “Yellow” or “caution” zone and 250 degrees is my “Red Light” limit where I pull over and high-idle in Neutral until the temp is down. Being conservative, chicken and slow on a mountain down-hill, we have toured the Rockies about 5 times over the years and I have never seen 250 degrees.

Parenthetical anecdote: our first coach was a 1988 U-280 with no retarder and I worried about transmission temps because, in Colorado, it wasn't unusual to hit 250 degrees and I would back off. Met an RV'er in a park who had been a Fire Truck salesman for 20 years. and he scoffed at my concern. He said that at a fire, pumpers were “locked” at wide-open throttle for 8 hour at a time and were always at 250 degrees in the transmission (Allison 4-speed).