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Discussion Starter · #1 ·
Hello. I've had my Terrain Diesel for about 3 months now and I have put about 6000 miles on the car. Everything seems to be great except the gas mileage is not what I have expected. I'm averaging a consistent 28mpg combined City/Hwy. My first trip out of town I drove 164 miles and got 30mpg, and made the return trip the same day and still did 30 mpg. I've heard stories of 40 plus MPG! What kind of gas mileage are you experiencing? I would like to know before I take it into the dealer. No code are showing up and seems to run good.
 

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Have been driving the nox version for nearly 9000 miles now.
The best 50 miles mpg i got was 48 mpg ( i suspect there was a bit of wind assist)
Highway with no wind etc typical is 42 mpg

My hand calculated average is near 36 mpg (the mix is typically 60% highway 40% town and dirt roads...the dirt roads are very slow speed).
 

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I drive 160 miles a day, combination interstate and state highways. The past week has been just over 44 mpg according to the trip computer. Prior to that I did a few months exclusively city driving, mileage then was about 32 mpg.

I've never experienced mileage as low as you are reporting. Sounds like somethings up!
 

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Any luck on this issue ?

The only other thing i could think of is if everything is working and sounding fine...is tire pressure.

By any chance are your tires below 30 psi ?

I am not sure what tuning that could go wrong in a diesel to make it consume more than it should without a CEL....(turbo not working properly ...so that mixture is too rich) ? I believe there are sensors for all that so a CEL should have appeared.

Some diesel head expertise needed
 

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Discussion Starter · #5 ·
Any luck on this issue ?

The only other thing i could think of is if everything is working and sounding fine...is tire pressure.

By any chance are your tires below 30 psi ?

I am not sure what tuning that could go wrong in a diesel to make it consume more than it should without a CEL....(turbo not working properly ...so that mixture is too rich) ? I believe there are sensors for all that so a CEL should have appeared.

Some diesel head expertise needed

My tires are at 36psi. This week I have done exclusively city driving and I'm getting 30mpg.
 

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City driving in the south with the air running probably means your engine doesn’t auto shut off at a stop. While 30mpg sounds low, it makes sense, where the diesel really shines is on the interstate without all of the traffic lights.
 

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Not to rub salt in your wounds, but I have the 1.5 gasser and over 5800 miles (since new) I have averaged 30.2 MPG. My best 25 mile MPG was 37. I drive about 30 miles one way to work, but its almost all on 2-lane back roads at a max of 50MPH. That's got to be helping.


One thing I found is... If I leave my Driver Info Center (DIC) on "Fuel Mileage" I find that I subconsciously drive it differently in an attempt to beat my "high score" on fuel mileage. It makes a difference of about 2mpg when I do that.



Tim
 

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Cowracer--I think the difference is that charlemagne's 30 mpg avg is city driving. I believe your's (if I read correctly) is a combination city/highway, or primarily highway. My 2.0 gets me about 19-20 (or less) mpg of pure city, but pure highway will return 31+. I think charlemagne's 30 mpg city is great!
 

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My tires are at 36psi. This week I have done exclusively city driving and I'm getting 30mpg.

That is good the diesel is rated at 28 mpg or so for pure city by EPA


I think you should just check your gas mileage average manually just to see what you get i cannot believe that you get the same mileage on the highway ....just might be computer problem rather than a real problem.


So if you are getting an average of 34 to 35 per tank in mixed driving then you are fine.
 

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Cowracer--I think the difference is that charlemagne's 30 mpg avg is city driving. I believe your's (if I read correctly) is a combination city/highway, or primarily highway. My 2.0 gets me about 19-20 (or less) mpg of pure city, but pure highway will return 31+. I think charlemagne's 30 mpg city is great!

Yeah, I don't do much 'city' driving (I.E. Stop and go, block to block kind of stuff), but I guess my idea of 'Highway' is different. I always think of 'highway' as bombing down the interstate at 70-75.



One thing about diesels (and I know a thing or two about them) is that diesels are their most efficient at a steady RPM, and they lose efficiency while accelerating. By 'efficiency', i mean amount of energy extracted from fuel consumed. Ever see a big truck smoke from the exhaust while taking off from a stop? That smoke wasted fuel. The fuel requirement of a turbo-diesel is set by RPM, Load and Boost level. Its a trade off at lower RPM as load may be pretty high (accelerating from a stop, say) and boost is not up to full pressure. Generally, diesels over-fuel in this condition. The old mechanical injection ones were horrible at this, because you fueled it to a level, assuming full boost because there was no feedback mechanism for the boost level. You just had to assume, and put up with the smoke. Newer computer controlled Direct Injection diesels are better at it, but the issue still remains.



The best thing you can do to account for this is easy acceleration from stops. Don't just hammer the accelerator. Toe into it, give a second or two for boost and load to stabilize and then squeeze on more pedal in a gradual manner. I'm not saying drive like granny on her way to sunday service... just be a bit mindful of the fact that the time that elapses from the pushing of the pedal to where the engine 'catches up' is the most wasteful region in which to operate a diesel.



Tim
 
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Discussion Starter · #12 ·
City driving in the south with the air running probably means your engine doesn’t auto shut off at a stop. While 30mpg sounds low, it makes sense, where the diesel really shines is on the interstate without all of the traffic lights.
I guess I was thinking I'd get better city mileage? I have two Mercedes 300d & 300TD and they both get 26mpg all day and night! they will run on anything! Those were the days......
 

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Why don't you try to get the mileage trend chart enabled on your DIC...you can see what it is doing trend wise in different driving condition. I am still baffled that you get 30 mpg city and kind of the same in mixed or highway driving.
Here is mine while driving on back roads you can see the jumps from paved road steady speed at around 45 mph and dirt roads at 15 mph.
 

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Discussion Starter · #14 ·
Why don't you try to get the mileage trend chart enabled on your DIC...you can see what it is doing trend wise in different driving condition. I am still baffled that you get 30 mpg city and kind of the same in mixed or highway driving.
Here is mine while driving on back roads you can see the jumps from paved road steady speed at around 45 mph and dirt roads at 15 mph.

TIZAN. I think I will do that! Ill let you know what I learn. Thank you for the chart/picture.
 

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Why don't you try to get the mileage trend chart enabled on your DIC...you can see what it is doing trend wise in different driving condition.
Here is mine while driving on back roads you can see the jumps from paved road steady speed at around 45 mph and dirt roads at 15 mph.

I have a 2018 LT diesel and either I've missed your pictured DIC display on mine or GM has changed the DIC selections. I keep mine on the "sliding scale" mpg display that shows my all time mileage for a 50 mile increment (47mpg) and the running mpg as I drive. My overall average for 4000+ miles is 34 mpg, mixed conditions but seldom much traffic. I agree with those above that the diesel thrives on the interstate, even with the rolling hills.
Our 1.5 Premier has a best of 40 mpg, (rare and one time), overall average, same conditions, is 28.3.
Howard
 

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I have a 2018 LT diesel and either I've missed your pictured DIC display on mine or GM has changed the DIC selections. I keep mine on the "sliding scale" mpg display that shows my all time mileage for a 50 mile increment (47mpg) and the running mpg as I drive.
Howard

I have the diesel LT too..this chart is not there by default but you can add it.
press the left arrow key on the DIC keys on your steering wheel ...then select settings....then move to info or information and select...you'll get a selection of screens you can enable or disable...you can monitor oil pressure for e.g ...this chart is "economy trends" or something like that.
 
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