I'm curious about something.
When I start the truck in the morning and it's not cold enough for high idle to kick in, I will let the truck warm for a minute or two, then set the parking brake, put the truck in gear and hold the rpm's around 1000 (not enough to reach stall). This helps the engine warm quicker (I'm assuming from the load), but the tranny temp needle hardly moves after 10-15 minutes.

When high idle kicks on in even colder weather (like this morning with the temp reading 5 degrees), the truck will high idle for 15 minutes and the engine temp is warmed up (just like the previous method), but the tranny temp is much higher. The tranny temp will actually go DOWN as I start driving.

I read my owners manual and it states that the exhaust becomes restricted during high idle to increase engine temps, but I could not find (or didn't see) how it forces the Allison to warm. Does anyone know.

I search using "allison" and "high idle" as search terms and found alot of posts, but no answers.

Thank in advance.
Chris

It's not stated anywhere but starting in MY06 the trans will lock up the turbine inside the torque converter to add extra load to the engine when High Idle is active. Main purpose is to heat up the cab faster.

It's essentially like what you are doing by putting it in gear with the parking brake on. But in this case it applies C3 and C4 (I think), which locks up the turbine shaft stalling the converter without sending any torque to the wheels. But don't worry, it's designed not to overheat the trans.

Cool info! I did notice that durring high idle the trans would build a bit of heat or more so than if just let ideling.

Ledfoot. I do the same thing. Wish the high idle would kick on in warmer weather. Or there was a switch or something to fool it.....but I've been told fooling circuts in the motor to get the high idle to kick on is a :badidea:

It's not stated anywhere but starting in MY06 the trans will lock up the turbine inside the torque converter to add extra load to the engine when High Idle is active. Main purpose is to heat up the cab faster.

It's essentially like what you are doing by putting it in gear with the parking brake on. But in this case it applies C3 and C4 (I think), which locks up the turbine shaft stalling the converter without sending any torque to the wheels. But don't worry, it's designed not to overheat the trans.

:cool2: Thanks for the information. I love this site.