In my ACE 30.1, with F53 chassis, 6.8L V-10, 5-speed transmission, the tranny temp gauge doesn't read temperatures. It simply shows a range, with the upper end indicated in RED (which I think means "Get ready to walk"). However, pulling a 3700-lb Toyota Highlander, even on a hot summer day and going up long, fairly steep hills to Cashiers NC, temperature never got close to the red zone. In fact, it barely budged off of center of range. It's on my list of someday projects to install an actual temperature gauge, but so far I'm not worried about it.
Incidentally, there are lots of transmission fluid temperature/lifespan charts out there like the ones posted above. Here's one that I bookmarked:
http://www.digi-panel.com/trannyoil.htm. The operative text for fluid temps measured at the pan/sump is this:
- 150° F= The minimum operating temperature. Note: It is possible in low ambient temperatures to overcool the transmission with auxiliary oil to air coolers. Oil to water coolers in standard factory radiators will normally not overcool a transmission.
175-200° F= Normal pan oil temperature operating range.
275° F= Maximum allowable oil pan temperature for short durations during long hill climbs.
300° F= Damage occurs to internal transmission parts, including warpage of metal parts, degradation of clutches, and melting of seals. Transmission oil oxidizes, (forming varnish-like substances causing further clutch slippage and compounding heat build up) and transmission oil life is extremely short.
See also the chart for fluid life vs. temperature. The Ford owners manual calls for a fluid/filter change at 60,000 miles, but I'm thinking that a 25,000-mile interval may be cheap insurance. I hope to educate myself on the issue as I rack up the miles (only 7500 miles on the rig now).
