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2015 Promaster 1500 136" low-top gasser.

Love my van, but I'm not getting anything close to 17-20 mpg.
Having to fill up almost exactly every 200 miles, 24 gal tank makes that close to 8 mpg.

I do live in the N GA foothills, and I carry around a fair amount of gear (guessing about 1000 lbs).

Also, I do have to run the rpms above 2500 to merge, get out into traffic, etc.

Judging by what others have posted, even considering all that, I should be getting at least 15 mpg, right?

I dunno where the gas is going...

I runs well, if I hadn't done the calculations I wouldn't know there was a problem.

What am I missing?
 

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Something is definitly wrong. Now it boils down to regular old diagnostics. What you absolutly DON'T want to do is just start guessing and throwing parts at it. You'll be blindly replacing the highest quality OE parts with parts store junk, and still not solving the problem.

Any competent independent mechanic will be happy to diagnose it and let you do the work yourself. He will read the computer and look at things like temp sensors, long and short term fuel trims, o2 sensor responses, etc.

The most likely cause of low mpg is the computer thinking the engine is cold when it isn't. Temp sensors, or possibly the system just needs burped.
 

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When driving steadily at 65 mph on a flat stretch of interstate, what does your Instant MPG read-out indicate? If it is in the 17-20 range, then your engine is probably functioning properly and you need to figure out how the gas is disappearing. If it is significantly less, check to see if you are in 6th gear. (Just bump the shifter over into Manual and the dash will display what gear you are in, then bump it back into Drive.) If you are in 6th, then your transmission is probably functioning properly. From there . . . I'm not sure what to suggest next, but that's a starting point . . . .
 

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Do you have anything extremely non-aerodynamic on top of the van?
 

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At 65 on flat road my 159" ext will show 28-39 mpg. Do you do a lot of stop and go driving? Drive with 2 feet? Have ladder racks? Short trips where the engine doesn't warm up? There are many other variables but that is the lowest mpg I've heard a ProMaster get. I would take it in and have them check for leaks.
 

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2015 Promaster 1500 136" low-top gasser.


Having to fill up almost exactly every 200 miles, 24 gal tank makes that close to 8 mpg.

(snip)

I runs well, if I hadn't done the calculations I wouldn't know there was a problem.

What am I missing?
Based on the info above, you have no way of knowing if you are you calculating correctly. The only way to do this is to record the amount of gas going into the vehicle, not to estimate that amount based on the tank size. Since you haven't done that, you can't eliminate two possible causes of miscalculation: the shutoff at the fuel filler at the gas station you use may be triggering early; or your low-tank indicator may not be functioning correctly. Since you aren't recording the exact number of miles and dividing by the exact amount of fuel going in, you can't know if you have a correct mpg. It seems to make sense to start there.
 

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Don't mean to derail the thread, but how do I get the MPG reading to show at all times on the console? It was there, I messed with updating the date and time, now I can't locate the MPG setting in the menu to get it back. Thanks in advance!
 

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Press the button at the end of the windshield washer stalk over and over, eventually it comes up?
 
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I noticed that on some fillups the nozzle would click off early (specially in CA) and I had to manually top it off. I also had a few instances of the avg mpg being stuck on 8ish. I just reset it., I also hand calculate the fuel used by the miles traveled if I want to get a good real number. The dash thingy is close but a pencil is better. If my Dodge Ram diesel computer was correct I would have kept it sine it said I was getting 23+, but by hand I was getting 15-16.
 

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Discussion Starter #12 (Edited)
Thanks for the responses! Here's more info...

I do have a ladder rack on top with a 32 footer...

My gas card makes me enter in the odometer every fill up, I'm constantly going 210-230 miles between fill-ups. (I'll find some real numbers and calculate a more legit #)

Yes, a fair amount of hilly, and city traffic, not much hwy speed driving.

My display doesn't show trip or MPG, I'll do more research to see if it can be set to do it. (tried a while back it it just wouldn't do it)

I bought the van used from a car lot, who got it from a rental fleet up north (was in service 9 mo with rental fleet, had 19K miles on it, stripped down base model, drove it off the lot for $20,500.00)

I agree about not throwing parts at it :)

I don't fully understand how this transmission works and could be the sole source of the problem (ie. my ignorance).

Edit: Just watched a vid about how to make MPGs show. Discovered my Trip button is non-functional...
 

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I do have a ladder rack on top with a 32 footer...

a fair amount of hilly, and city traffic, not much hwy speed driving.
Those factors, plus 1,000# of gear in van, could easily put you in the 13 mpg range. If you tend to accelerate hard, and you don't anticipate stops and ease off on the gas, you could lose another 1-2 mpg. But still, that shouldn't take you to 8 mpg.

I don't fully understand how this transmission works and could be the sole source of the problem.
I mentioned the transmission earlier on the chance that it is staying in too low of a gear. High RPMs would hurt your gas mileage. (If you are using TOW mode, it might hurt your mileage a little.)
 

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Even out in the mountains, mine gets around 16 mpg just driving around country roads.

Run some Techron FI cleaner thru the system? I did that recently.

I did notice a 2 mpg hiway drop after getting all 4 solar cells mounted up top. I'm sure that dirtys up the air flow and causes drag. But the 22+ mpg hiway I get in flat land is acceptable to me.
 

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2015 Promaster 1500 136" low-top gasser.

Love my van, but I'm not getting anything close to 17-20 mpg.
Having to fill up almost exactly every 200 miles, 24 gal tank makes that close to 8 mpg.
I easily have 1000 pounds of A/C, Refrigerator, etc. inside and on top, and I consistently get 8.9 driving around town in my Winnebago Travato.
When I get out on the highway, I get closer to 17, though.

You're saying you're getting 200 miles for 24 gallons, but I don't think that's right. Sure, your gas card makes you put in the odometer, but I *know* you're not putting in 24 gallons every time! I "ran the tank dry" this last fillup (drove about 35-40 miles past the 50 miles left warning). I was "topping it off" past the auto-shutoff several times - to the point that I was genuinely scared I was going to overfill. (the tone/sound of the gas going in changed a bit, and I figured I was filling up the fill-pipe...), and it only took 22 gallons...

You might try aCar on your phone for better mileage calculations (and a place to keep other maintenance records, as well). It requires you to put in your odometer at each fill, but it also requires you to put in how much gas you took, and the price you paid (so you can get a 'cost per mile' and 'cost per month' out the other side).
 

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Discussion Starter #16
Ok, heres what I got:

last OD reading 37065
put in 18.58 Gal. at 37281

so 216 miles = 11.62 MPG

Better than 8 but still a bit low I think.
 

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Ok, heres what I got:

last OD reading 37065
put in 18.58 Gal. at 37281

so 216 miles = 11.62 MPG

Better than 8 but still a bit low I think.
Hi,
I think you need a couple more fillups to tell.
The PM is hard to fill to a consistent point when you fill it up -- it tends to shut off early in an inconsistent way. So, I'd say, do a couple more tanks and try to fill each time to a consistent point.
I think you will end up with better than 11.6.

Gary
 

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Trying to hand calc can be very inconsistent. I hand calc'd vers the computer every tank for the first 5,000 miles. My conclusion, you get one mpg less than what the computer says. Just made a trip from FL to CO, 2100 miles and computer says 19.5, so really got 18.5. Carrying about 900lb, 70mph. Two things that make the biggest difference is speed and wind. I had a stretch in Kansas that I had a strong tailwind and was getting 22. Soon as I changed direction, wind was side on, wasn't even getting 17.
 

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This is why I encourage you guys to buy an obd reader. For a $12 dongle and an $8 phone app, we could know most of the engine parameters and determine if there's a problem. If it's burning extra fuel, that would show up as a value in the long term fuel trim. My reader also shows me an accurate amount of fuel in the tank in gallons so we could know if its a fullup problem. And it shows actual coolant temp - the dash gauge is just for show.

Search ebay for ELM reader, buy Dash Command from Palmer Software on the app store. At the very least, you'll be able to establish a comparison against my vans, and a comparison against yourself when future problems arise.
 
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