43221B

Have any of you noticed that the GL 320 transmission holds a lower gear than it needs to when driving under 50 mph? I've been using the upshift paddle to shift up a gear when driving at non freeway speeds and the mileage is going way up. Where I was getting 20-21 in city driving I'm now getting 23-24 mpg. Either there is something wrong with my transmission or it is geared low to keep the trans from hunting when going up hills. It is flat where I live so that is a non issue. I'd be curious to know if others notice the same thing.

lkchris

I suspect you can reduce pressure on accelerator pedal and get it to upshift. It's all drive-by-wire so it doesn't take much.

43221B

Actually, it will not. For instance, there are several 3-5 mile long stretches of road that I fequently take that have a 35 mph speed limit. The police are bad so I will usually set my cruise control on 39 or 40. The engine will run around 1400 or 1500 rpm at that speed. If I upshift with the paddle, it will move up a gear and will run closer to between 1200 to 1300 rpm. I'm assuming that puts it in 7th. The diesel has no problem running at that speed and doesn't shift down even on gradual inclines. If I go to accelerate with anything more than a gradual press of the accelerator, it will immediately shift down.

I guess my point is, if everyone elses 320/350 does the same thing, then I guess mine is shifting properly and there is more mileage to be had. Certainly, it probably makes for a more enjoyable driving experience if the transmission doesn't shift the second you go to moderately accelerate at those speeds. Not that I really need to eek out another 2-3 mpg but it is sort of fun to see the mpg number climb on the dash. By the way, this is when the engine is completely warmed up.

DucatiNut

Had an XC90 that did the same thing but more so in winter. Even thought the engine temp gave said it was up to temp it would hold a lower gear until it had been running quite a while and everything was hot, not just the water temp. Next time you return from a trip, turn around and head out again over the same road and see if it repeats with a hot engine and transmission...

43221B

No, I'm talking about when it is completely warmed up. Don't get me wrong, I'm not complaining. I think the transmission has a setup that delivers a good driving experience. I just think that the shift points are set to run the engine a little faster than it needs to run when taking fuel economy into consideration. If everyone elses 320/350 is set up the same way, perhaps it was purposefully engineered that way to allow the driver to manually shift up for fuel economy's sake when cruising at those speeds. In a lot of stop and go traffic, it would be annoying if the engine ran so slowly and the transmission had to shift down constantly. If you could let me know if any of your diesels do the same thing, I'd appreciate it.

robalo220

Yes you are correct. I have an 08 and it is slow to shift when you get on it also. It holds the gear almost to redline. Even if you use the paddle shifter, it still is slow to shift. Now if you are driving like you describe, mine acts the same way. It is essentially the same engine and tranny as in the ML 320. I had an 07 ML 320 and it had better shift points. I think due to the extra weight, they designed the GL's tranny to shift later as to give you the feeling of more power. It annoys me also.

Fourdiesel

On the '07 - '08s, the transmissions are supposed to be adaptive - that is they are supposed to 'learn' from your driving habits and move the shift points accordingly. I assume the '09s are the same.
In my experience on my '08, the car is pretty dumb - it doesn't learn very fast! I also would like the tranny to remain in a higher gear longer when moderate accelerator pedal is used. I find myself using the paddle to upshift (never to downshift - that shifts you 3 gears) all the time. I wish there was a way to make the driver's input a higher priority in the tranny shift algorithm.
It will be interesting to see if yours learns any faster than mine did/does.

DucatiNut

Well I know my CLS55 adapts to my driving but I did not know the GL does. If that is the case, search the forums here to see if you can reset the ecu (key to on position, depress accelerator fully and hold for 5 seconds, switch off, release pedal and wait 2 minutes .... if I remember correctly) Makes a HUGE difference in my CLS!

StevethePilot

I've done paddle shifts at highway speeds and gotten it to shift up "one more gear" to (can't believe I'm even saying this) 7th. What was interesting to me was, my loaner C230s my dealer gives me do the same thing. It's likely most folks drive those like they stole them. I feel like it's a combination of adaptive shifting (like others have said) and just too many gears. Now, on some days I've had the transmission hold a low gear for a long time, as if it were trying to, I don't know, heat up the engine or maybe clean the ... is it a filter in the exhaust? But the weirdest thing is backing out of my driveway most mornings, I have to give a lot more accelerator push than I'd expect, just to get it started. Then, once it's moving, no problem. Like on a manual transmission when you ease out a really long throw clutch, not like a sudden clunk, so it feels controlled and not like something's broken. But I'm due for service, so I'll ask my SA what he thinks.

STP

LEOSOPHIE

The 550 does exactly the same thing under 50, drops 200 rpm and fuel mileage improves.

LEOSOPHIE

My 550 stays in a lower gear in cruise control and will upshift with the paddle. Also you are very savy with these cars, do the diesels start in 2nd gear as the 550's do?

slim nicky

What makes you say they start in 2nd gear?

alx

the only reason it will hold gear is if drivetrain is cold (after a cold start 7th gear is unavailable for quite some time in auto mode)

or...

you are pushing it... try slightly lifting off the throttle to make tranny upshift... the 7g can be pretty much shifted through the throttle...

alex

43221B

This is another issue altogether. It took me a while to train myself (my foot) not to let the tach go over about 3200 rpm. My technique for quick acceleration is to depress the accelerator so the tach quickly goes up to just over 3000 rpm. I hold it there or just sightly depress the accelerator until it shifts up a few gears while maintaining a rev range between 2100 and 3000 rpm. Once it shifts into what is probably 4th or 5th and the engine is running around 2200 rpm, you can feel all 400 lbft of torque and it takes off. I have a feeling that it problably loses 4 or 5 seconds to the 450 between 0-30 mph and then gains a couple back above 30 mph on the way to 60. I'm not quite sure why it even allows you to run the engine over 3500 rpm. When you floor the accelerator, it seems like an eternity for an upshift to occur and then when it does, the engine is above the optimal torque range. I'd be curious to know if the 0-60 time would be improved at all following a more calculated approach to applying the throttle.

If there are any better techniques out there, I'd love to hear them.

dgiturbo

I believe Mercedes should reprogram the diesel transmissions to work best with the diesels motors. The 7 speed tranny's all try to work as if they are mounted to a higher revving gas motor, and not a torque monster. I am sure the bean counters had some input here to save a dollar, but the engineers should have put their foot down on this.
And yes, even on my ML, there are times just around 45-50 MPH where I am really trying everything to get the tranny to upshift just 1 more gear so my RPM's can drop. The only way I can do this is to accelerate to 55, then slow back to 45. Not always the best choice on a 45 MPH speed limit road.