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Discussion Starter #1
Good evening all,

I've had my 2.0 Automatic Dart for 4 years, 90,000 commuting 120 miles a day. It's been a great car, but over the past year the mileage has gone from ~36 down to a measly 26; the majority being on the highway. In my quest to get better #'s, I've flushed the oil with Roayl Purple, changed out the spark plugs, air filter, and primary/secondary 02 sensors.

The car doesnt run rough at idle, partial, or full load throttle so I cant bring myself to replace the injectors (yet). There is no DTC's or CEL either. I just crossed 140,000 and would like to keep this car going as my DD for a little while longer.

Any help or insight/experience with this would be beneficial, thanks!
 

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Check for dragging brakes, especially the rear brakes.
 

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Discussion Starter #3
Had that happen last year on the rear driverside. Replaced all rotors, pads, and wheel bearing. It'll coast fir days. It doesnt feel like theres anything in the drivetrain that's stopping the car
 

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If you replaced the tires, did you go oversize?
 

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Discussion Starter #5
I have Federal 595 RSR 225/45/17 tires. I've ran these since I've had the car, changed about every 20,000 miles. There are more economical tires out there, but that's been a constant while the MPG's have been decreasing.
 

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Do you still have the belly pan?
 

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No, that thing was ripped off a few years back courtesy of NY plow trucks
If it's gone, that is definitely part of why your mileage is decreasing. Deyeme Racing has a replacement.
 

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If it's gone, that is definitely part of why your mileage is decreasing. Deyeme Racing has a replacement.
That's not going to cause a 10mpg drop. It definitely helps with aero dynamics, but there is something else going in with that significant of a drop. As you said, that might be part, but I don't think it's a significant part.

@jolio1994
Alpine already touched on the tires. Have you tried to add an fuel system cleaner? At that mileage it might be good to start adding some every so often. It's possible with all those miles, there might be some build up internally, causing the dramatic decrease in mileage. It could be exceptionally bad due to winter fuel (if you live in the cold). Injectors should be fine, I don't know the exact time to replace them though. Looks to be about $100 if you want to replace those soon. Not terrible 2015 DODGE DART 2.4L L4 Fuel Injector | RockAuto

Has the car been aligned lately? It sounds like you really hit everything on the head already in terms of maintenance needed. Here is the link to the belly pan Deyeme Racing : Online Shopping: Our Products, it's called Undercarriage Aero Shield, Front (Closeout Panel and Belly Pan) (DMR)
 

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I have seen Darts on the road with sections of the belly pan just flying in the wind under the car. If sections of the belly pan are catching the wind, it can't be helping your gas mileage. Here is the thread about the Deyeme shield:
I noticed you said you replaced rotors, pads and wheel bearing, but did you replace any calipers? If a caliper is not releasing, that could be a significant drag. If any of your wheels feel hot after a half hour trip, it could be a bad caliper. With a jack and jack stands lift the rear and those wheels should spin easily. The front end has to spin the diff so there will be some drag but you should not hear the pads holding the rotors. There could be a little resistance but not a lot to where you really have to push hard to turn the wheel.
 

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I have seen Darts on the road with sections of the belly pan just flying in the wind under the car. If sections of the belly pan are catching the wind, it can't be helping your gas mileage. Here is the thread about the Deyeme shield:
I noticed you said you replaced rotors, pads and wheel bearing, but did you replace any calipers? If a caliper is not releasing, that could be a significant drag. If any of your wheels feel hot after a half hour trip, it could be a bad caliper. With a jack and jack stands lift the rear and those wheels should spin easily. The front end has to spin the diff so there will be some drag but you should not hear the pads holding the rotors. There could be a little resistance but not a lot to where you really have to push hard to turn the wheel.
I would agree checking with this. The rear calipers are known to sticking. I replaced mine for this exact issue, then got a rebuild, brand new kit and they did the same thing a few months later. Luckily replaced under warranty.
 

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Good evening all,

I've had my 2.0 Automatic Dart for 4 years, 90,000 commuting 120 miles a day. It's been a great car, but over the past year the mileage has gone from ~36 down to a measly 26; the majority being on the highway. In my quest to get better #'s, I've flushed the oil with Roayl Purple, changed out the spark plugs, air filter, and primary/secondary 02 sensors.

The car doesnt run rough at idle, partial, or full load throttle so I cant bring myself to replace the injectors (yet). There is no DTC's or CEL either. I just crossed 140,000 and would like to keep this car going as my DD for a little while longer.

Any help or insight/experience with this would be beneficial, thanks!
Have you replaced your wheel bearings yet? Those will cause a drastic change in MPG when they are worn. The stock ones are known not to last very long, at 140k miles you should definitely replace all 4.
 

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Discussion Starter #13
While I haven't check the calipers, I have put the car in neutral while coming to a stop. The brakes aren't sticking and all wheel bearings have about 20,000 miles.

I've never had an alignment for as long as I've had the car, but toe/camber wear is even on all 4 corners. Car also drive straight as an arrow.

The only thing left to do for me is add a fuel cleaner/stabilizer. If that doesnt work I'll move to new fuel injectors, and after that... well, that's really all that's left.
 

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If it's running smooth, save your money and get the Deyeme belly pan.
 

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Discussion Starter #15
Got somewhere good today! Last night I put in some Mystery Oil in the engine oil as well as the fuel system and did about 150 miles today on the highway.

Averaged 35mpg at 75-80mph which is about 8-9 better than what I was getting at that same speed. I'm going to do an oil change tomorrow and top it off with a little more mystery oil as well as throw in some actual fuel injector cleaner and see where it gets me.

This is awesome, now I can focus on my Audi wagon! 😁
2020-01-12_07-36-19 by Joel Francisco
 
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