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So i purchased my ram late December 2016, when I was driving from Kentucky to Michigan I was getting about 23.5 - 24 average mpg at about 78 miles per hour. Now doing the same drive I am getting about 18 mpg. How ever I have changed two things tires and air filter. I am running factory size tires they are cooper atp' s. My air filter is a drop in k&n. I cant imaging that the tires would decrease fuel economy by 5-6mpg nor the air filter. Does anyone have this issue? Truck has about 30k miles on it. I use mobile 1 5w-20.
 

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Same time of year? Winter gas has robbed me of about 1.5 to 2 mog this year. So if you have heavier tires and winter gas that can be it. Which engine do you have? I know GTYankee has seen and MPG decrease in his ecodiesel this past few months as well.
 

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As mentioned winter gas decreases MPG! Sometime more other times not as bad,, Must be their mixture ! BUT are your tires 10 ply ? If so they are real heavy and sucks gas, my buddy lost abut 4/5 mpg ,, Please update what you find out !
 

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I have never even come close to 23-24 mpg in my Ram. The best I ever had was 21 mpg from my Z71 and that was holding a speed around 60 mph on fairly level drive with no wind.
 

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the USA government mandates that Summer Gasoline has to follow these rules
May 1 to September 15 for refiners and terminals, and June 1 to September 15 for gasoline retailers.

The US Environmental Protection Agency (EPA) says conventional summer-blend gasoline contains 1.7 percent more energy than winter-blend gas, which is one reason why gas mileage is slightly better in the summer. However, the summer-blend is also more expensive to produce, and that cost is passed on to the motorist.

States can Offically request a variance to the June 1 to September 15 rule on a case by case basis

==============================================

My Eco-diesel uses Diesel #2 all year around
Diesel # 1 is winter diesel & very seldom available in most States
 

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Discussion Starter #6
Sorry guys my truck is a big horn 5.7 hemi with the 3.21 rear end, yes same time of year, tires are 10 ply.
 

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It's not uncommon to lose 2 MPG by going to the much heavier 10 ply tire. Also are you sure its the stock size? Most people usually go a little bigger and taller and the taller will throw you mileage off a bit.On another note I have a 17 Laramie Crew with the Hemi and 3.92's and if I reset the evic as soon as I get on the interstate I will barely get 20 MPG at 79 MPH and that's on flat ground. I usually average around 17 MPG in mixed city/rural driving.
 

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I hope I'm not over simplifying this, but you mentioned driving at 78. 78, of course, is the magic number where your MDS stays on and 79 is where it kicks off. No matter what the engine load is, if you're going 79, your ECO light will go off, and you're running on all 8 cylinders.

On the first leg of a 1400 mile trip from PA to Maine (first trip in the truck), I'm running 80MPH on I-80 in PA, and noticed that A. my Eco light was never on and B. My MPG was around 15.5. Through some experimentation I found the speed at which the ECO light stays on, and later confirmed the 78MPH threshold through some internet research. Once I set the cruise control to 77 MPH (so that even when overshooting the setpoint, I never made it to 79), my MPG went up to over 21.

I use this knowledge on my daily commute to run in 4 cylinders as much as I can. I know the places the ECO will kick in, so I ensure my cruise control is on 77 in these places. However, once the load (based on the incline, curves, etc.) is such that the ECO goes off with the cruise set at 77, I bump it up to 80, since I'm going to be running on 8 anyway, I'd rather run at 80MPH (in a 70 zone), which is pretty much the threshold where the PSP will leave you alone around rural interstates in PA.
 

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I'm betting it's a combination of the winter blend gas, the cold temps in the Detroit area, and those 10 ply tires. All 3 combined could certainly result in a 4-5 mpg loss. I'd suspect you'll gain a few mpg's back once it warms up, but I'd still expect a few mpg loss with the heavier tires.

In regards to the ECO light and MDS, it is true that the ECO light will go off when the speed hits 79mph. However, the ECO light is not an indication whether or not your MDS is on. The ECO light simply means you are driving most efficiently. MDS will actually engage at times even when the ECO light is off.
 

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That is interesting I was under the impression that MDS only came on when the ECO light was on but that it wasn't on everytime it came on. So all MDS were ECO but not all ECO lights meant MDS.
 

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That is interesting I was under the impression that MDS only came on when the ECO light was on but that it wasn't on everytime it came on. So all MDS were ECO but not all ECO lights meant MDS.
I had always thought the same thing. It made complete sense to me that the two were tied together. But after some reading and threads on here, I learned that the two are not tied together.

I know you can't believe everything you read online, so I'm hoping I have the correct understanding of the MDS/ECO light operation.
 

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That is interesting I was under the impression that MDS only came on when the ECO light was on but that it wasn't on everytime it came on. So all MDS were ECO but not all ECO lights meant MDS.
Same here. It would make sense that MDS would come on when you're driving most economically (ECO)., but under what circumstances would you be driving most economically on 8 cylinders? Seems to me that if you're on 8, and the threshold to run on 4 hasn't been met, you're not really in ECO. And what's so magical about 79 MPH that ECO isn't on. My "instantaneous gas mileage" gauge can be pegged high when coasting down hill at speeds over 80 MPH, but the ECO light will be out. Slow down to 78, and the ECO light goes on.....but the instantaneous MPG is still pegged. Seems to be a little voo-doo here.

Interestingly enough, the ECO light on in my Challenger is not limited by speed, and it's much easier to actually hear the 4 cylinders cut out. I don't notice the sound in the exhaust on the RAM. On the car, though, ECO and MDS always happen together. I can feel/hear it and see the light come on at the same time....always, no matter what speed.
 

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It would be nice to see the kind of fuel mileage increases some of you guys say you're seeing with MDS. I actually saw my mileage decrease by 1 mpg on my commute with MDS on. 20 miles each way, 95% highway miles. But with several large hills to climb and descend. The highway speed limits range from 50 to 60 mph. None of that is interstate. I am now in the habit of disabling MDS as soon as I put my truck in D.

70 mph speed limits are only a dream for us where I live. The highest I see in my corner of the state is 60. And WSP will often pull you over for doing as little as 5 mph over the posted speed limit. The county boys usually give you closer to 10 over unless it's been a slow month for them.
 

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It's not uncommon to lose 2 MPG by going to the much heavier 10 ply tire. Also are you sure its the stock size? Most people usually go a little bigger and taller and the taller will throw you mileage off a bit.On another note I have a 17 Laramie Crew with the Hemi and 3.92's and if I reset the evic as soon as I get on the interstate I will barely get 20 MPG at 79 MPH and that's on flat ground. I usually average around 17 MPG in mixed city/rural driving.

Dayum, that is exceptional! I just went from PA to CO on I 70. Was down to as low as 13 at one point in Kansas. Lucky to get 15-16 going across Missouri and Kansas. All doing 74-78 mph.
Never get over 17 in the south on I 95 @ 74 mph in the summer.

I am so jealous :(
 

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That is interesting I was under the impression that MDS only came on when the ECO light was on but that it wasn't on everytime it came on. So all MDS were ECO but not all ECO lights meant MDS.

I can confirm that MDS can come on without ECO and ECO can come on without MDS.
Just watched this happen earlier in the month, but it seemed to be rare and with certain circumstances with the MDS and no ECO. The only sign was the sound and instant MPG readings.
 

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Interesting. Thank you. I can't hear the MDS difference. At least I have never ntocied it. But then again audio quality is not my thing. Most speakers of even decent quality sound the same to me. And audiophile I am not. Maybe this is why messing with the exhaust is lost on me.
 

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I can barely hear it, but usually do feel it more often than not.

I have a single exhaust so it is a bit quiet. But, the ride is fairly stiff, so I feel it more.
 

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I can confirm that MDS can come on without ECO and ECO can come on without MDS.
Just watched this happen earlier in the month, but it seemed to be rare and with certain circumstances with the MDS and no ECO. The only sign was the sound and instant MPG readings.
Thank you. This is my first Ram, has single e haust. Once I can drive with the windows down, will try to listen for it.
 

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It is easier to feel than hear, but you can hear it slightly - sounds flat.

If you want to feel it, if you coast down a hill and then ever so lightly give it a bit of gas as you transition from down to flat, you should feel it and maybe hear it for a few seconds before all 8 cyl. kick in if you give it just a bit more pedal.
 

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MDS and eco light are definitely not related.
 
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