# Fading fuel economy



## KyleB (Mar 12, 2017)

I find that I'm having a hard time keeping my fuel economy above 40mpg. At least according to the DIC. Commute is 90% highway, about 20mi, and I drive like an old man. Each tank seems to be a little lower. The only thing I can figure is that it's been quite hot and I'm running the AC full blast. Is that really enough to have that big of an impact on fuel economy or should I bring this up at my first oil change? Only 3k mi on the odometer right now.


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## Tomko (Jun 1, 2013)

Running your AC on recirc and at the lowest fan speed possible will result in improved fuel economy. 

I have set my best ever fuel economy with AC left on, in recirculated and fan speed at one.


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## obermd (Mar 3, 2012)

The AC can really suck down the power in our small engines. Lower the fan speed and switch to recirc.


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## Rivergoer (Mar 30, 2017)

40 mpg Highway on a diesel? That doesn't sound right at all.

2014 Gen I 2.0 diesel with 68,000 miles, I just drove 250 miles across the California desert today in 105 degree heat and AC blasting, recorded 51.1 mpg at 60 mph (would've been better if not for a 15 mph headwind). 

Even if I was doing 70-75, mileage would've been about 45-46 mpg. While AC does load the motor and reduces fuel efficiency, I've found (on the Gen 1 diesel anyway) AC doesn't have as much impact as wind, terrain and city driving.


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## Merc6 (Jun 8, 2013)

If the diesel is like the Gen 1 1.4s were, economy was all over the place till you reached a certain amount of miles. On my Eco that transition was like 8000 miles and my Accord was like 9000 miles. Also being diesel, how are the regens set up for MPG in the Gen 2?


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## Jmaj (Apr 9, 2017)

Perhaps the aero shutters are open more in the high temperatures or it's windier.


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## jblackburn (Apr 14, 2012)

Should be well over that I'd think. I do 40+ at 70+ mph in a gasser with the AC cranked. Not blasting though - I'd freeze.


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## starspangled6.0 (Apr 16, 2016)

A\C has a pretty dramatic effect on my Gen 1, at least on the instant readout. Perhaps the reason yours is low is a combination of the A\C on and the car going through a regen?


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## Aranarth (Oct 18, 2016)

Change the air filter.

Diesels require lots of airflow!


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## jblackburn (Apr 14, 2012)

Aranarth said:


> Change the air filter.
> 
> Diesels require lots of airflow!


Never seen anything need an air filter with 3000 miles since it left the factory!


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## IndyDiesel (May 24, 2015)

jblackburn said:


> Never seen anything need an air filter with 3000 miles since it left the factory!


I haven't either, I changed mine at 28000 and honestly it was pretty clean. I will probably check mine before replacing it next time


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## grs1961 (Oct 23, 2012)

KyleB said:


> ... and I drive like an old man...


Don't do this.

These small turbo-charged diesel engines like a bit of stick, so once the temperature needle has started to move give it some wellie!

You don't have to plant your foot, but give it a chance to spool up and clear its tubes.

*Then* switch on the cruise control and let it take care of things.


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## johnmo (Mar 2, 2017)

grs1961 said:


> Don't do this. _(drive like an old man)_
> 
> These small turbo-charged diesel engines like a bit of stick, so once the temperature needle has started to move give it some wellie!
> 
> ...


My experience bears this out some. When I'm really, really careful with the throttle, I can maybe eke out another MPG or so in some situations, but generally the car seems to like running a little faster and deep on the throttle when accelerating.

My last tank was a little lower. I've been running the A/C and not trying much to be efficient. But... "lower" for me is 54 MPG.


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