post #17 says the dealer got 32mpg on their test? what was the distance traveled? you also say you use the trip computer and come nowhere near that number? i play with my trip computer and can reset it while i am driving on the highway and i get 33mpg approx initially. than after 5-10 miles it drops to 30mpg or so. you should get the same for your rig. so, you get 30+ on the hwy and you get off the road and into your driveway and it should still read high 20’s? maybe they drove on the hwy for a mile and pulled over and had the jeep towed back to dealer? haha
I saw the 32.7 MPG for their “trip” when I retook possession of the car, and I’m sure that number will be used in the dispute with Fiat Chrysler. Unfortunately, I have NEVER been able to achieve that kind of fuel economy with this car. I wish I could, because then we wouldn’t be having this dialogue. If I were getting even 21/22 MPG for “mixed” driving (the stated city estimate), I would accept mild disappointment. I live in a suburban area, never drive in heavy traffic, and have driven numerous pretty long trips (300+ miles), so it’s not like I’m driving only city. But I’m averaging 16 MPG in total, including all fuel purchases and miles. I’ve been complaining about the fuel economy from the start. 12,000 miles later, I’ve still got no answers. Really frustrating.
One point that I was getting at in a not very clear manner is that it’s entirely possible to have a hard fault with no diagnostic codes being set. Logic says this should not happen, but…
I had earlier mentioned the possibility of a faulty engine coolant temperature sensor. Many years ago my Mercury got a little wonky. It seemed to run fine but fuel mileage dropped from the normal 26 on the highway to 22 on the road.
No diagnostic codes were set. No Check Engine Light. I decided to test the ECT sensor with an ohmmeter and found it way out of range. Replaced the ECT and the fuel mileage returned.
I’ve also seen hard failures of the crankshaft sensor, speed sensor, MAF sensor, and so on with no DTCs being set. Just something for consideration anyway.
try a reset on the hwy? at least we all we know whether the jeep can hit 30+ mpg at least initially.
Yes, I know how to do that (reset), and have optimistically done it hoping that I would actually be getting the fuel economy that I’m supposed to be getting. Unfortunately, testing sensors is beyond me, but perhaps I can find someone to do that…
+1
Even though my brother’s new Hyundai Azera had a bad engine coolant temp sensor, the Check Engine Light never came on.
As somebody else said, ask to have the car tested with you in it, see how they got 32 mpg. Could have been driving 20 mpg on a back road for all you know.
whew, its like pulling hens teeth.
you have done the reset on the hwy?
and you got what initially?
i expect you to say you got 33mpg initially, and than drove home. and it said 25mpg avg
and than drove to work the next day and now the average is 15mpg?
my former car listed fuel used and miles driven.
you used 1.2 gal and drove 30 miles. avg is 25mpg
This tells me the 16 MPG figure is a long term average.
Would an engine that is burning that much excessive fuel show too-high unburned hydrocarbons in its exhaust? Or is the catalytic converter handling it like a champ?
The fact that the dealer got 32 MPG rules out, to me at least, a mechanical problem, unless the dealer were cheating.
As others have asked, could the OP check the mileage driving at a fixed speed, say 50 MPH, on an open highway? reset the computer (as you are driving), drive for 10 miles under the cruise control, see what the computer says is your MPG. See if you get 32 MPG.
I know that I will get well over 40 MPG under the same conditions. (Forester, base engine)
A few weeks ago, I replaced an inaccurate coolant temperature sensor . . . no fault codes whatsoever
On this particular engine, I was able to screw in a mechanical coolant temperature gauge on one bank, while still having the suspect coolant temperature sensor screwed in on the other bank
So I monitored the cluster, scanner and my gauge all at the same time
There was over 20 degrees difference between my gauge and the factory coolant temperature sensor’s reading
I replaced the sensor and retested. No more discrepancies
Not sure I completely agree with that . . . on this particular vehicle, the factory provided no specs for testing. Often, the manufacturer will provide a chart. At a certain temperature, you should expect a certain resistance and/or voltage. No such luck here. I looked in the paper factory service manuals and the manufacturer’s technical website, which we subscribe to at work. Nothing. Hence the mechanical temperature gauge
The average MPG display may or may not be accurate. My 2010 Kia was the first vehicle with that feature. After I had acquired 3,000 miles (thorough break in) I started monitoring MPG manually. Using the same gas station and 9 times out of 10 the same pump the MPG very closely matched the miles traveled/fuel added calculation. Fuel added was out of my hands as Oregon still prohibits self serve by the general public and attendants are not allowed to add fuel after the pump automatically shuts off. My average MPG display is very accurate and automatically resets when the tank is filled (how does it know?). The first time I left the gas station from their driveway to a 55 to 60mph state highway I used appropriate (spirited) acceleration. About 0-60 in 10 seconds or so. Not the car’s potential 0-60 of 6.9 seconds (Road & Track road test). When I glanced at the speedometer to ensure I was up to highway speed I noticed the average MPG was about 5mpg! That made sense going from zero mpg and accelerating to 60mph in less than 1/4 mile. About 8 miles on the highway at 55-60mph in 6th gear (1,900 to 2,000 rpm) resulted in average mpg of 35 plus. When I completed 10 miles round trip of city driving average mpg was about 28. Return with highway driving was about 30mpg. I have no way to reset my display between fill-ups. OP says the Jeep can reset the display manually. Did the dealership do that once they entered the highway to achieve 30+ mpg?. If they did they were attempting to cheat the OP. If they did it out of ignorance they are incompetent. A few years ago I overheard 2 men. One asked the other how he liked his new Chevrolet Malibu? He replied that it was great but the average MPG display was malfunctioning. When he was parked with the engine running mpg would decrease although he was not traveling any miles. His buddy suggested he have the dealership check that out. I decided attempting to educate 2 individuals that ignorant was futile.
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My sister leased one, not sure what year, but they told her to come in once a yer for a computer upgrade, no charge, maybe you just need a computer upgrade.
A bad thermostat or temp sensor won’t directly trip a fault code. Unless it causes misfiring, or an out-of-range oxygen content in the upstream oxygen sensor, it’ll generally not cause a code. The ECU doesn’t monitor the T-stat directly. A defective T-stat can, however, cause the engine to take too long to reach operating temperature and kill gas mileage. But that would be highly unusual. Usually they fail by either not opening, which will cause overheating, or not closing, which would have rendered your heating system’s marginally operative at best.
Your symptoms don’t sound like a bad T-stat, but I thought I’d add a bit of clarity on the T-stat question. It remains a possibility.
My wild guess would have been driving style, but your mileage with the loaner would seem to rule that out.
Re: the measuring question, the only accurate method of measuring mileage is to divide the fuel pumped to “shutoff” at three or more fillups into the miles traveled, preferably using the same pump every time to reduce the shutoff point as a variable. The key is to use some method such as mile markers or known distances as variables. Gas pumps are calibrated, so you can rely on their accuracy, but your odometer could be off.
Of course, tying a moose to your hood would make your gas mileage drop too. 
Just trying to add a bit of levity. No offense meant.
The cooling system is monitored by the PCM, the engine temperature must reach a certain temperature before other monitors can run.
If the engine coolant temperature fails to reach 170 F in a calculated amount of time the PCM will set fault P0128, Thermostat Rationality.
It is possible to have a failing thermostat and a fault not be set because of short trip length or driving too slow but sooner or later the failure will be detected.
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Yep, my Camry set a code before I ever noticed the engine wasn’t quite getting up to temp. Bad tstat…
Thanks to everyone for the thoughtful responses, much appreciated.
I’ll do a few fill-ups and try to keep track specifically of my highway miles (separate from driving on local roads).
My guess is that the end result is going to be extremely close to the 16.5 MPG that was showing on the fuel economy calculator for the 3,000 miles before Jeep did its test.
And just to clarify, it was corporate - not the dealer - sending a representative to the dealer to calculate the fuel economy and evaluate the vehicle. My car cannot achieve 32.7 MPG in normal driving conditions - even when manually resetting the fuel economy calculator while on the highway and already at driving speed - so something out of the ordinary had to have been done in their test (specific MPH, drafting behind a truck, etc.).
I really don’t see how Fiat could get almost 33 MPG and you get 16, unless it’s driving habits. Do the highway test again, but let the cruise control drive the car, keep your foot off the throttle.
I guess it’s possible they cheated, but unlikely.
i guess it does not matter what your computer says when you reset it on the hwy. 1 day later or maybe 4 or maybe 2 weeks later it says the average is 16mpg. i am just curious what it says initially. which we may never know
Is the 4WD lock on?