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I am sorry if this has been posted before. I’ve done some google search and found what appear to be other issues (potentially unrelated) with the cruise and a downhill descent. At this point, I’m not sure if I have a problem or if this is just what the van does.

I have a 2019 Touring Plus with just over 2.5k miles on it. I just finished a nearly 2k mile trip out of mountainous WY where we have very fast highway and interstate speeds (80 mph).

When cruise is engaged at these higher speeds (65-80 mph) and I begin going down a steeper downhill, the van will (I assume) downshift to slow me down. In this process the RPMs shoot up to 4K+. Eventually when the road flattens out for a bit the van will finally decide to upshjft again and the RPMs decrease to normal. The van drives so well and the RPMs are almost always below 2k so this behavior was alarming.

I can’t imagine that type of revving is great on a transmission. This hasn’t happened with any other vehicle I’ve driven. Is this normal? Is this ok?


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I would say it is normal, my Audi does the same (and the 1999 Ram Van 1500 I had before did it as well). If you go downhill, the cruise control wants to keep you roughly within your set speed range. So the only way to break the van down is to downshift, to make the resistance (=breaking) of the engine stronger.


When making my driving license in Germany, I also learned to purposely downshift when going downhill and to use the effect of the "engine breaking". The purpose is to be easy on the regular breaks to prevent them from overheating and excessive wear.


Shouldn't create any issues for the transmission, since this is within Spec...


Some better explanations can be found here: https://www.picknbuy24.com/column_352.html
 

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I experience the same thing. It is disappointing because I pride myself on keeping the RPM's low. I've become tuned in to when the van, while on cruise, will attempt to downshift. I'll hit the cancel cruise button and let the van coast. RPM's stay low, gas mileage is great. Only in the Rockies has the van not been able to slow itself with the engine brake. Did pretty well through quite a bit of Appalachia, still the engine brake doesn't seem to do much. Seems like it slows the van down more in town, making coasting a bit annoying as slower speeds.
 
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That operation is completely normal and intentional. As you surmise, it is the car downshifting to maintain speed on the downhill run. Spinning the engine at 4.5k RPM is not a problem. The redline is 6.5k so it isn’t really reving it all that hard. Fuel consumption isn’t an issue because in this situation because the car is in Deceleration Fuel Cut Off (DFCO) - zero fuel is being fed to the engine. If you bring up the fuel economy display it will show 99MPG - the highest it goes, but also a bit of a misnomer. If in metric, or using an OBDII monitor it will show 0 liters per 100KM - no fuel use. The kinetic energy of the rolling van is being fed back through the wheels and transmission to spin the engine, so you are getting free miles at that point.
 

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Shouldn't create any issues for the transmission, since this is within specs... [/url]


This is exactly what I was looking to hear.

I think the solution (although it is not a problem) me will be to switch out of cruise. I’d rather get the mileage on some of these hills than the breaking power.

None of the hills are dangerous mountain bends I would need to apply brakes on. I may not be able to maintain a perfect 75 or 80 but it will be a rough equivalent.

Thanks all


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As already mentioned, coasting the car in neutral or drive gear wastes fuel and is less safer than a controlled deceleration offered by “engine braking “. Not sure why many don’t prefer it. Using the gravity to go downhill (without burning fuel) is the best way to save energy and the environment (if you care about it).
 

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Of all the things you save through engine braking, wear and tear on the brakes is the most important. People who go down slope while constantly on the brake just don’t know how to drive.
 

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Transmission braking is great, when it's really called for. but on most downhills I break cruise and downshift as needed. You get DFCO either way, but if a higher (but still perfectly safe) speed on the downhill happens, that's fine. It's not like the transmission can see that the downhill is almost over, the road is straight and there's no traffic. You've got to drive the van, not just steer it.

"coasting the car in neutral or drive gear" can be the right move in some circumstances, as can downshifting in others. Downshifting, or "coasting" in gear (that's not actually coasting) is still braking. While the system isn't pumping gas into the cylinders, if it slows you down it may not be the most fuel efficient way to get where you're going. Spending kinetic energy to save potential energy (gas) may only get you closer to when you need to spend more gas to move forward. If you're not in cruise or on the gas, odds are you're getting DFCO without the tach vigorously and noisily pointing it out or the system actually slowing you down. Because face it: disc brakes or transmission braking, the effect is the same. Don't be on the brakes more than you have to.
 

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I feel like people who are really confused about this have never learned to drive a stick shift. It's amazing how many people, even in hilly places like California, that have no idea what that "L" gear is for. Failing to downshift on an uphill will only make the engine stall, but failing to downshift on a long downhill can kill you from brake failure. When driving a manual, it's just obvious how bad it is because you're used to thinking about what an appropriate gear for the situation is. In fact, when I took my driver's test in Sweden, they would have failed you if you had attempted to go down a steep downhill in the highest gear while riding the brakes.

Engine braking is a renewable resource, it does not wear anything out, as long as you don't overspeed the engine. Even if you don't have a hybrid... :smile2:
 

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That operation is completely normal and intentional. As you surmise, it is the car downshifting to maintain speed on the downhill run. Spinning the engine at 4.5k RPM is not a problem. The redline is 6.5k so it isn’t really reving it all that hard. Fuel consumption isn’t an issue because in this situation because the car is in Deceleration Fuel Cut Off (DFCO) - zero fuel is being fed to the engine. If you bring up the fuel economy display it will show 99MPG - the highest it goes, but also a bit of a misnomer. If in metric, or using an OBDII monitor it will show 0 liters per 100KM - no fuel use. The kinetic energy of the rolling van is being fed back through the wheels and transmission to spin the engine, so you are getting free miles at that point.

I'm not sure I agree with the 0 MPG going down hill. I like to think of myself as a high miler and the best I've do on average driving around town, highway, hills and all, is 30.7 MPG.


I always drive with the fuel economy display on. I've noticed when I'm going down a hill at 25 MPH I get a 99 reading on the display. If it let it coast up to 35 MPH the van shifts and my mileage drops to around 30 MPG. That's always bothered me. It's not is cruise control just driving.


Thoughts?
 

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That's just the transmission doing its job, and one of the reasons why automatics FTL.

The transmission doesn't know that you're going down a hill and everything's fine, it just sees that because of the lack of back pressure, it should upshift. And presto! The engine isn't acting as a brake and letting DFCO give you infinity miles per gallon any more, you're in a higher gear and it's gently pushing you forward. The self-contained system is operating as designed, oblivious to the world outside the van.
 

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So you're designing a car. Everything about it is completely stunning, better by far than anything else in its class. And then at the last stage, to mess everything up, snatch defeat from the jaws of certain victory, you drop in an automatic transmission. For the loss.

The 9 speed is a great automatic, way better than the 6 speed it replaced, which was also a really great automatic. But automatics don't know what the road is doing, they don't know what other traffic is doing, they don't know what you're trying to do and they won't let you do things that don't fit into their programming. Upshifting while going down a hill is a classic example. The van doesn't know that loafing in DFCO is the right thing to do here, it just knows that its mapping says it's time to upshift.

It's really, really good at what it does, but it's still an automatic.
 

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So you're designing a car. Everything about it is completely stunning, better by far than anything else in its class. And then at the last stage, to mess everything up, snatch defeat from the jaws of certain victory, you drop in an automatic transmission. For the loss.

The 9 speed is a great automatic, way better than the 6 speed it replaced, which was also a really great automatic. But automatics don't know what the road is doing, they don't know what other traffic is doing, they don't know what you're trying to do and they won't let you do things that don't fit into their programming. Upshifting while going down a hill is a classic example. The van doesn't know that loafing in DFCO is the right thing to do here, it just knows that its mapping says it's time to upshift.

It's really, really good at what it does, but it's still an automatic.

I guess the operative word here then is "Automatic"! Got it, thanks.
 

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I am sorry if this has been posted before. I’ve done some google search and found what appear to be other issues (potentially unrelated) with the cruise and a downhill descent. At this point, I’m not sure if I have a problem or if this is just what the van does.

I have a 2019 Touring Plus with just over 2.5k miles on it. I just finished a nearly 2k mile trip out of mountainous WY where we have very fast highway and interstate speeds (80 mph).

When cruise is engaged at these higher speeds (65-80 mph) and I begin going down a steeper downhill, the van will (I assume) downshift to slow me down. In this process the RPMs shoot up to 4K+. Eventually when the road flattens out for a bit the van will finally decide to upshjft again and the RPMs decrease to normal. The van drives so well and the RPMs are almost always below 2k so this behavior was alarming.

I can’t imagine that type of revving is great on a transmission. This hasn’t happened with any other vehicle I’ve driven. Is this normal? Is this ok?


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I have the same issue only mine has done this going up hill rpm jump from 2000 to 5000 this is not normal happened 3 times in 2500 miles!
 

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I have the same issue only mine has done this going up hill rpm jump from 2000 to 5000 this is not normal happened 3 times in 2500 miles!
Thats normal. When going up a grade using cruise control the transmission will downshift to maintain the set speed and that will cause RPMs to rise.

The rise is more dramatic in modern cars with a lot of gears, like the Pacifica. Its criuising in 9th gear, and then its downshifting to 3rd or 4th gear going up the grade and the RPM differential is pronounced. When cars had 4 and 5 speed transmissions the jump wasn't as noticeable.
 
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