Hill Climbing

Cummins and Allison are efficient automatic pieces of engineering: EGT, downshift, temperature, RPM overspeed limiter, etc.. I take a look at the provided gauges once in a while and I just enjoy the automatic ride.

Arnie,

Certainly, one CAN just let the Allison "do its thing".

But, by definition, a transmission is REactive (seeing what happened behind you and the heavier the vehicle, the further behind you it looks because of MOMENTUM.

A driver can be PROactive-- anticipating what is happening in FRONT OF YOU.

Based on my tour of the Allison plant and the Q&A I will let the transmisson do the shifting as programmed as the tour guide suggested. If you choose read the manual if have a different opinion JMO.

Jerry, The temp sensor goes before the turbo. I drought you have one from the factory. I think you could find a temp sensor to monitor the air from the CAC, you could do in and out.
Brett, That brings up the question. What does the factory think are acceptable EGT temps and for how long? As you know I am running a Banks Economind Diesel tuner and the Banks IQ. I can run in the first setting that adds nothing and did that on a trip to get a base line. The hottest temps were when I had cruse on and the ECON engaged. The computer would try to maintain speed in the gear selected. I did see temps over 1300 but turning off the cruise and dropping a gear will drop EGT temps.
Bill

On most of my hill climbing, I use my "max-performance" technique. I speed up before I began the climb, and as soon as the engine RPM starts dropping I hold the fuel pedal to the floor, and let the machine select whatever gear it needs.
I don't do enough hill climbing to worry about fuel mileage, and don't mind the engine going up to 2,400 RPM (8.3 Cummins 350 HP 1,050 lbs of torque).
It has never overheated.

wolfe10 wrote:

2oldman wrote:
Downshifting before the hill is easier on the tranny.

Would like more information on that one-- this is an Allison 3000 series. Torque converter is locked in all higher gears.

The only reason I would downshift (down arrow) is if the transmission in hunting between gears or you are overheating.

The OP is doing it EXACTLY correctly (per Cummins): As long as you are not overheating, let RPM lug down to peak torque RPM before downshifting.

And by doing THAT....your highway speed can vary considerable. Getting to the top of the hill first isnt any big deal but maintaining a constant...fluid like...highway speed is MUCHO safer

Lots of opinions/theories. As a 50+ year manual transmission user, I prefer to shift down an automatic manually, as I can see what is up ahead, ie increased grade, or another grade, or a sharp curve coming up, and prefer to downshift before the transmission decides to. Maybe just a carryover from my manual days. Never have had a problem on grades - up or down.

WILDEBILL308 wrote:
Lots of interesting replies. I find it interesting that no one mentioned EGT temps when climbing hills. You can have dangersly high EGT temps long before your water temp goes up.
Bill

Bill,

Unless one has modified the engine (chip in newer, larger injectors/ moved plate in older) the engine manufacturer has limited fueling to avoid dangerously high EGT's.

Said another way, EGT's on a stock engine would be "interesting" to watch, but would not reach dangerous limits. Exception would be running below peak torque RPM at high throttle positions.

My CAT didn't come with an EGT, but I can see how it would be useful information. Where is the probe normally installed - upstream or downstream of the turbo? or is the probe already there for the ECM?

Also - what about inlet air temp? With all the worry about plugged up CACs, I'm surprised that the air temp on the output side of the CAC isn't monitored as well.

I expect I'd get all of these from an engine monitor app on my tablet.

Lots of interesting replies. I find it interesting that no one mentioned EGT temps when climbing hills. You can have dangersly high EGT temps long before your water temp goes up. I think every diesel coach should have at least a Boost, EGT and transmission oil temp gages. I will watch and if EGT temps start to get high I will manually down shift. The hill that got my water temp up was not the big climes but a gentle grade that couldn’t have been more than 2-3 degrees. The problem when I caught it was I was running cruise but the hill wasn’t enough to make the transmission down shift. So the computer had the boost maxed out to maintain speed. The problem it was about a 20 mile climb. You didn’t feel like you were on a hill till you looked behind you.
Bill