Manual Automatic Mode
 

I took a trip recently to Ohio in my 14 Elantra. During my drive I encountered miles of rolling hills. When I hit the hills my transmission would downshift to maintain my cruise control set speed. Every downshift met with a significant reduction in fuel economy on my ScanGuage. I decided I would shift into manual mode to see if there was anything to be gained by locking the car into high gear.

My car would not upshift to a higher gear in manual mode while climbing so I tried it the opposite way. I climbed the hill locked into 6th gear. When my fuel economy settled I shifted into normal automatic mode which triggered a downshift to 5th gear, with each downshift to 5th I lost 4 MPG.

I guess I'm wondering if anyone else has experience with locking in high gear? Does the car normally shift down to protect the weaker 6th gear or is it done to ensure on-demand power is available.

find what the lowest speed you can shift to 6th is and keep it in 6th

From the 100+ hypermiling tips:

44) Cruise control - when not to use it
Only use cruise control on flat roads. On hilly roads, cruise responds to changes in grade - by feeding in more throttle on the uphill and releasing on the descent - in the exact opposite way an efficient driver would

56) Drive with load (DWL)
AKA "target driving". Put most simply, this technique is accomplished by choosing a "target" rate of fuel consumption and ensuring you don't fall below it on hills (or in very strong winds, or any conditions which cause load to vary for a given speed).

In other words, you will back off the accelerator and lose speed (possibly also downshifting) as you climb, and gain that speed back on the descent.

It's far more efficient than pressing the accelerator more and more to maintain speed on the way up a hill and then releasing it down the other side.

DWL is how an efficiency minded person can greatly outperform cruise control in hilly terrain.

Obviously the ability to use this technique without adversely affecting other drivers depends on the traffic situation.

As well, fuel economy instrumentation is required to DWL/target drive to the maximum extent, though it can also be done using a vacuum gauge, and to a much lesser extent by the seat of the pants.

I think that is the key question - and no, I can't answer it. I have the same issue with the auto box in my car. It will change down when I would have kept it in a higher gear with a manual box. My initial impression was that this is to ensure on-demand power is available, which is something I would sacrifice.

I have recently tried experimenting with the manual shift controls, which in my case are paddles on the steering wheel. Very boy-racer F1 style. I have come to the conclusion they are unusable, for a couple of reasons. The one that is relevant here is that the auto will override my settings if my manual gear selection is outside of its comfort zone. I can't think why the manufacturer would have made it work that way unless it was to prevent damage, so maybe my initial impression (about changes being intended to maintain availability of on-demand power) is incorrect.

As to what to do about it, I have been wondering whether it can be changed in software. I wonder if I plugged in to the OBD port and logged all the data flying around I might find messages that control the gear changes. If so, maybe it would be possible to inject my own messages. This would of course be foolish if I just broke my gearbox.

I drove a rental Hyundai Elantra once and it would lock 6th gear in manual mode up a hill.

Turns out, the 1.6L engine wasn't really capable of pulling 3000 lbs up a slight hill in 6th lol, I had to go down to 4th.

Jedi_sol,
I was road tripping, my primary goal was to get to my destination as quickly as possible, fuel economy was a secondary concern.

SDMCF,
You brought up a good point about the computer overriding driver input. I am sure if things got to a point where driveline damage was possible the computer would force a downshift.

serialk11R,
My car is equipped with 1.8 liters of fury. It has the lowest first gear I have seen in a small car. Reminds me of the Chevrolet Diesel I drove at work. It had an Allison transmission that felt like the brakes had been applied as it shifted down to 1st. Anyway, I pulled 6th through the rolling hills without drama, but it's definitely no powerhouse.

The downshifts are quicker than what an eco driver would want, they come up with some tradeoff btwn sport and economy that the average driver likes. I haven't heard of any cars that have weak top gears that needed to be babied. Keep it in as high a gear as you can.

In a G1 Insight, I've had instances where I've run into hills that have required 2nd gear to climb. Leaving it in higher gear will also run the risk of running down the hybrid battery, and converting between electrical and mechanical energy is often more lossy than simply downshifting and rev'ing it a bit.

However, this car is more the exception than the rule. It has a 67HP 3 cylinder, and a 5th gear that that is under 2000RPM at (lower) highway speeds.