I'd like to understand how these things work in an 08 Sienna AT.
As a starting point, when in D and I go 65 mph, the RPMs are 2000. If I go up a hill with enough incline, it seems to 'downshift' and the RPMs will go to about 2300 to get back to 65 mph,(I will call this 4.3 in the following). If however, the shift lever was in 4, and I went 65 mph, the RPMs would be 2800. So by going to 4.3 has the transmission actually shifted, or is there some extra 'turbo' mode the engine goes to or what?
I've seen the terms 'lock' used in discussions, and get the idea that 'lock' is a good thing. Which of the 3 scenarios above am I in 'lock'?
The reason I'd like to know better, is that I pull a ~2000 lb popup RV camper (Aliner), and have often seen the advice to drive in 4 rather than D. When I tried this on a trip, I saw that transmission temps were definitely higher (15+ degrees). I know that heat is bad (and I recently installed a transmission cooler to great effect thanks to the great thread on this forum), but hear that a lot of shifting is bad also. If I go D, and run a little faster on the downhills, and especially if I let up (and slow down a little) on the uphills, I can usually (not always) avoid the 'shift' to 4.3 . Rare that it shifts down to 4.0. So the question is, is dropping down to 4.3 as bad or the same as the AT shifting down to 4.0? Given the lower noise, better gas mileage, lower presumed engine wear of lower RPMs, and the lower trans temp, I much prefer pulling the rig in D instead of 4. Can anyone shed any light on these areas? Thanks.
As a starting point, when in D and I go 65 mph, the RPMs are 2000. If I go up a hill with enough incline, it seems to 'downshift' and the RPMs will go to about 2300 to get back to 65 mph,(I will call this 4.3 in the following). If however, the shift lever was in 4, and I went 65 mph, the RPMs would be 2800. So by going to 4.3 has the transmission actually shifted, or is there some extra 'turbo' mode the engine goes to or what?
I've seen the terms 'lock' used in discussions, and get the idea that 'lock' is a good thing. Which of the 3 scenarios above am I in 'lock'?
The reason I'd like to know better, is that I pull a ~2000 lb popup RV camper (Aliner), and have often seen the advice to drive in 4 rather than D. When I tried this on a trip, I saw that transmission temps were definitely higher (15+ degrees). I know that heat is bad (and I recently installed a transmission cooler to great effect thanks to the great thread on this forum), but hear that a lot of shifting is bad also. If I go D, and run a little faster on the downhills, and especially if I let up (and slow down a little) on the uphills, I can usually (not always) avoid the 'shift' to 4.3 . Rare that it shifts down to 4.0. So the question is, is dropping down to 4.3 as bad or the same as the AT shifting down to 4.0? Given the lower noise, better gas mileage, lower presumed engine wear of lower RPMs, and the lower trans temp, I much prefer pulling the rig in D instead of 4. Can anyone shed any light on these areas? Thanks.