[MarkD]

I bought Promaster 3500 RV 2 weeks ago in NOLA and drove home to Florida. First day I got 24.5 mpg, 70 mph, I-10, level interstate, 70 degrees rain and wind. The second day I got 13.5 mpg, 65 mph, I-10, rolling hills, FL panhandle, 60 degrees, windy. Now at 1900 mi ODO I get 12.5 mpg, 70 mph, level interstate, 70 degrees, no wind. I don't know why the fuel economy would drop so much in so short time. The first day it would stay in 6th gear with cruise set 70 - 75 mph. Now it downshifts to 5th gear 3000 rpm and instant fuel economy says 9 - 10 mpg until it speeds back up to 70 mph. It won't even stay in 6th with cruise set at 60 mph.

 

[MsNomer]

Not as drastic, but my mileage has dropped from 19-20 the first couple tanks to 16-17. People here talk about the cold being a factor, so I'm curious to test it now that we have warmer weather.

 

[Trecilla]

3000 rpm!!!!!????

I'm not a mechanic but my PM is a 2500 diesel and it's happy and purring around 1700 to 2000 RPMs in "D" and when I use manual, I shift at 2000 and then I stay around 1700 to 1900 RPMs. Is your PM diesel? It must be screaming at 3000 RPM, telling you something's not right . . . my guess.

 

[jostalli]

I believe it's gas. I read on this forum how heavy those REV's are. My guess is you should be seeing 12-14mpg on average.


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[Dwight]

With small engine, promaster is sensitive to wind and slight road grades. It can get amazing mileage, then bad with a slight road grade or wind.

 

[MarkD]

It is the 280 hp gas minivan engine. I agree 3000 rpm screams. It seems like with 6 gears they would have closer spacing and not such a big jump from 5th to 6th. It acts more like overdrive. If it would cruise in 6th on level ground then not a problem.

The Dynamax REV 24RB dry weight is 8024 lb. I have it loaded to about 8600 lb. The rear axle weight exceeds GAWR by about 300 lb but the front axle is light.

 

[MsNomer]

I didn't recognize that this is an RV. 11,500 pounds!! I'm impressed it can move.

 

[uncubed]

Leave it in 5th gear on windy days 24.5 mile per gallon on the first run does not seem right.
3000 rpms is no problem for this engine.
70 mph will be bad on gas. Try 65 mph and see what happens.
My van will not stay in 6th gear at 70mph with a head wind and it only a 159inch high roof.

 

[jmcdude]

Are you guys just counting the gear shifts or are they displayed somewhere and I just didn't notice. My mpg has been lousy. When I drove home 150 miles from the dealer in December I got 19 mpg doing 70. I was getting about 14 mpg driving local suburban traffic for while after that. With this cold winter we've had in Northern Illinois I'm getting about 12 mpg. I have the low roof 136 wb and probably have only added about 600 lbs between my upfitting and tools. I tend to drive pretty conservatively in an attempt to get the mpg up, not happening. The weather has just went from single digits to 60 this week so I'm hoping to see better milage. Has anyone brought up their mpg issue to a dealer and had an adjustment made in any way to help?

 

[Zyzzyx]

I'm smirking at the comments about 3000 rpm being 'screaming'.

Yeah, its a different engine altogether, but the 1.8 turbo 4cyl in my Audi A4 cruises at 3000 at 60mph, and loves it. Redline is 6500, and an inline four (even without balance shafts) is probably smoother than a V6.

 

[Chance]

I bought Promaster 3500 RV 2 weeks ago in NOLA and drove home to Florida. First day I got 24.5 mpg, 70 mph, I-10, level interstate, 70 degrees rain and wind. The second day I got 13.5 mpg, 65 mph, I-10, rolling hills, FL panhandle, 60 degrees, windy. Now at 1900 mi ODO I get 12.5 mpg, 70 mph, level interstate, 70 degrees, no wind. I don't know why the fuel economy would drop so much in so short time. The first day it would stay in 6th gear with cruise set 70 - 75 mph. Now it downshifts to 5th gear 3000 rpm and instant fuel economy says 9 - 10 mpg until it speeds back up to 70 mph. It won't even stay in 6th with cruise set at 60 mph.

The only way I can imagine a REV getting 24.5 MPG on level interstate at 70 MPH would be to have an extremely strong tailwind pushing you along. I've driven to and from California many times and know that winds out of the west can be quite strong, but even so that just doesn't seem right. Certainly not normal or expected.

Numbers in the 12 to 14 range seem about right to me. Anything in the 20+ range has to be an abnormality. There is just too much aero drag in an RV that size.

The Winnebago Travato reportedly gets up to 17 MPG under similar conditions, so 12 to 14 for the much bigger REV should be about right.

Regarding shifting from 6th to 5th with subsequent high increase in RPMs, I agree it's not optimum. It's one of the main reasons I'm waiting for a PM upgrade. Regardless, RAM needs to offer much lower gearing for cutaway chassis that will end up with huge box on top in form of Class C. The same gearing that is optimized for a ProMaster van with high roof can't be ideal for an RV that is about 50% bigger in cross section. Just doesn't make sence to me.

 

[uncubed]

jncdude pull the shifter over to your left at any given time and that's what gear you
will be in,it displays on the dash.
Example: Driving up a hill at 70 mph and rpms are around 2900, pull the shifter over
and will read 5. After you did this the transmission will not shift above 5th unless you
pull back on the shifter.
Pull away at a stop sign and feel the shifts but pull the shifter over when you think it
is 3 ,should now read 3 but now will not shift higher unless you manually do it.
Driving down a highway at perfect conditions at 70mph should read 2100 rpms
now pull the shifter over and it will read 6.
Whats in my mind and what I type should be pretty close here.I think. .

 

[uncubed]

(Regarding shifting from 6th to 5th with subsequent high increase in RPMs, I agree it's not optimum. It's one of the main reasons I'm waiting for a PM upgrade. Regardless, RAM needs to offer much lower gearing for cutaway chassis that will end up with huge box on top in form of Class C. The same gearing that is optimized for a ProMaster van with high roof can't be ideal for an RV that is about 50% bigger in cross section. Just doesn't make sence to me).
Unquote.
When I first got the PM this was one of my complaints as not staying in 6th gear in slight wind
or hill.
But now I just leave it in 5th ,don't even think about it anymore.
This little engine actually likes it and gets better milage in 5th than in trying to jump to 6th all the time under those conditions.

 

[FlyingVan]

Well, they have a very good reason for downshifting like that. They are programmed to do so. Let me explain.

The small gas engines, which pentastar is, do not have low rpm torque necessary to move the van. If you look at the torque curve on the gas engine you will see that the torque is provided at quite high rpms. Compare this with the diesel engine where the torque is availeble even down at 1400 rpm.

If the gas promaster would not downshift, every little hill or headwind would slow it down quite considerably and you would realize what a gutless dog it wrewould be. Hence the need to downshift, bring rpm up, bring torque up and your van can maintain speed or even accelerate. Now the diesel doesn't need to downshift since all the torque is available at cruising speed. When the hill comes the engine already provides the torque needed, so no downshift is necessary.

Transit's ecoboost is better in this regard, no downshifting, but you still get quite poor fuel economy. The Transit's normal aspirated 3.7 engine does the same as the promaster. If you want no downshift and good fuel economy, get the diesel. Folks, you cannot get blood out of a turnip. The laws of physics don't allow it.

For this reason I am a diesel fan. I drive a diesel car and a diesel van. And when the time comes to replace my Sprinter it will be another diesel van.

 

[30 Ounce]

Well, they have a very good reason for downshifting like that. They are programmed to do so. Let me explain.

The small gas engines, which pentastar is, do not have low rpm torque necessary to move the van. If you look at the torque curve on the gas engine you will see that the torque is provided at quite high rpms. Compare this with the diesel engine where the torque is availeble even down at 1400 rpm.

If the gas promaster would not downshift, every little hill or headwind would slow it down quite considerably and you would realize what a gutless dog it wrewould be. Hence the need to downshift, bring rpm up, bring torque up and your van can maintain speed or even accelerate. Now the diesel doesn't need to downshift since all the torque is available at cruising speed. When the hill comes the engine already provides the torque needed, so no downshift is necessary.

Transit's ecoboost is better in this regard, no downshifting, but you still get quite poor fuel economy. The Transit's normal aspirated 3.7 engine does the same as the promaster. If you want no downshift and good fuel economy, get the diesel. Folks, you cannot get blood out of a turnip. The laws of physics don't allow it.

For this reason I am a diesel fan. I drive a diesel car and a diesel van. And when the time comes to replace my Sprinter it will be another diesel van.

This is not correct. The gas engine has 90% of it's torque available at 1700 rpm's. It's actually quite a flat torque curve. The issue is that horsepower is what's needed to climb those hills and fight the headwinds. Horsepower is a rating of how much work is being done and torque is the force being applied. So horsepower = torque X rpm. To get the power needed to climb the hills the gas engine downshifts to increase the horsepower. Even if there was another gear ratio available between 5th and 6th it may still need to downshift 2 gears to raise the rpm's to get the horsepower necessary to climb those hills. Turbocharged gas or diesel engines can simply increase boost which of course increases torque and uses more fuel...but doesn't need to downshift. I think a turbocharged Pentastar engine would be awesome!

 

[jmcdude]

I am aware that kicking it into manual mode will display what gear you are in. If one wants it to stay in 6th while cruising why not just keep in manual mode? Won't it stay in 6th or does it kick down regardless. For me it's a non issue, 90% or more of my driving is non highway. For my purposes I like the way it shifts. My wife's car is a Mazda CX5 and I hate the way it stays in a higher gear instead of downshifting when going up inclines. I alway have to put in manual mode and downshift to get any power out of it.

 

[FlyingVan]

This is not correct. The gas engine has 90% of it's torque available at 1700 rpm's. It's actually quite a flat torque curve. The issue is that horsepower is what's needed to climb those hills and fight the headwinds. Horsepower is a rating of how much work is being done and torque is the force being applied. So horsepower = torque X rpm. To get the power needed to climb the hills the gas engine downshifts to increase the horsepower. Even if there was another gear ratio available between 5th and 6th it may still need to downshift 2 gears to raise the rpm's to get the horsepower necessary to climb those hills. Turbocharged gas or diesel engines can simply increase boost which of course increases torque and uses more fuel...but doesn't need to downshift. I think a turbocharged Pentastar engine would be awesome!

Tell me why then the diesel climbs better with way less horsepower than the gas engine. Then tell me why you don't see gas 18wheelers?

 

[FlyingVan]

Well, we can debate torque and horsepower till the cows come home and we would both be right. It jusis not that simple. But, horsepower and torque are related, then gearing comes into play, etc.
Anyway, torque helps at low rpm, while hp come into play at high rpm. But my point was that the gas engine needs that higher rpm to accelerate/mmaintain speed, while the diesel can do it easily at low rpms, no need for downshift.

Sorry for the thread hijacking.

 

[makevx73]

I am aware that kicking it into manual mode will display what gear you are in. If one wants it to stay in 6th while cruising why not just keep in manual mode? Won't it stay in 6th or does it kick down regardless. For me it's a non issue, 90% or more of my driving is non highway. For my purposes I like the way it shifts. My wife's car is a Mazda CX5 and I hate the way it stays in a higher gear instead of downshifting when going up inclines. I alway have to put in manual mode and downshift to get any power out of it.

Think of putting it in "manual mode" more as a "gear limiter"? It's not like a manual transmission in that 6th gear stays in 6th until you shift. All it does is limit how high the transmission will shift when you select a gear, it will still down shift as necessary.

 

[stanw909]

I think I can answer why the mpg difference is so drastic. It is the computer. The only way to really check mpg is to fill the tank. Drive it. Fill the tank again and divide distance drivin by how many gallons to fill it. The mpg computers seem to always be optimistic. It appears that the computer on these vehicles is very optimistic for the first thousand miles. Could this be a way to sell vehicles? Naw!!! A car company wouldn't do something like that.