I have noticed that when I warm up the coach (bringing it to operating temp both engine and trans) the trans. temp. rises quickly( to about 275) if I shift into drive and reverse while holding the brake ( 1 min. or more in each position). The temp drops quickly when back in neutral.
Is this normal?
No
My trans temp warms up very slowly at idle. When driving it stays around 190
It is either your intake manifold sensor or your water temp sensor. If it is cold my intake air temp will go up helping warm up the engine but the engine and transmission warm up slowly. I never see the tranny above 140 even when I am driving starting out. It hovered about 170 in normal driving then would run a couple degrees cooler then the engine. Never saw those higher temps unless I was losing a sensor.
If the transmission is in a gear that is in "lock up," there is no slippage and the transmission temp will be cooler. City driving will frequently see higher trans temps as the torque converter is "slipping" and making heat in the lower gears. Highway driving in coaches with the lock up feature in their Allisons will usually run about the same temperature as the engine.
Earlier Foretravels may not have lockup and run higher tranny temps. The transmission heat exchanger is designed to lower the transmission fluid temp. The higher the transmission temperature (over an extended period), the shorter the transmission life. Lock up will also be more fuel efficient as less energy is spent making heat.
I back up my driveway as the 4.xx to 1 ratio in first gear rapidly heats the fluid to over 300 degrees in the first 300 feet. Backing at 6.xx to 1 keeps slippage to a minimum and does not heat the trans over what the heat exchanger can control.
Pierce
If you have never seen Pierce's driveway you will probably not understand what a feat this is !!!
My little Mazda pickup had a difficult time going up. BUT THE RIDE DOWN WAS FUN !
Lon,
Check your idle speed.
If just a little high it will raise transmission temp when sitting still in gear.
Sitting in traffic it will go up. I put it in neutral between light cycles when sitting in heavy traffic but it shouldn't go up that fast.
I do exactly the same thing.