Getting horrible gas millage all of a sudden with my Big Horn 3500

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blackhammer

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My gas millage has dropped off considerably with my 2016 3500 Bighorn diesel. I used to get over 18 MPG around town and now I am lucky to get 12 MPG. And when I'm pulling my horse trailer with horses I was getting 10 MPG and a recent trip with empty trailer I was lucky to get 6 MPG. Any ideas what to look for before I take it to a shop. This just started. Thanks
 
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I don't have a 3500 Bighorn diesel but I have a 1500 Big Horn and my MPGs have actually gone up to 14.2 - 15.5 since the gas prices went up ... I have been driving it a lot more which is weird but a few people around here have also noticed their diesel trucks getting a lot less MPGs that before the prices went up ... hmmmm ... and this is with MDS turned off manually which I have been doing for over a year now ... I am averaging 380 miles per full tank the last 3 months ... last month was 372 miles and this last full tank was up to 385 miles

I wonder if it's the diesel?

20220118_083359[1].jpg
 

18CrewDually

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Cold temps, longer warm ups, short trips, winter blend fuel, idling, not hand calculating, ect. are all contributing factors.
With the frigid temps we're seeing the last week and short trips to the post office or town, mine went from 14.8 to 12.4 for fuel mileage. My first long trip it will recover. Driving cold stop & go around town kills diesel fuel mileage.
 
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Cold temps, longer warm ups, short trips, winter blend fuel, idling, not hand calculating, ect. are all contributing factors.
With the frigid temps we're seeing the last week and short trips to the post office or town, mine went from 14.8 to 12.4 for fuel mileage. My first long trip it will recover. Driving cold stop & go around town kills diesel fuel mileage.
Makes a lot of sense ... I used to drive a 2500 Ram a few years ago and in the summer it got up 23 mpgs, in the winter it would seriously dip as low as 10 mpgs ... I never understood that, but it was a company truck for Dish Network so they took care of any engine problems it had ....
 

Dennis Shellito

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My deleted and tuned 2011 was making over 23mpg empty on a road trip some years ago and filled up at a station in Lincoln, NE and the mileage immediately dropped to 10. I ended up having to run a couple of fill-ups with Bio Kleen additive to get the algae infestation cleaned up. There isn't a whole lot of things that will affect the fuel consumption of the diesels, other than quality of fuel, air filter restriction, and the over-all condition of the engine, and like was stated above, the climate.
 

Dean2

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Fuel quality is the number one issue that affects mileage, assuming your truck is healthy. I have seen as much as 40% worse fuel mileage by using lower quality summer fuel. The effect is even more pronounced when running winter blend fuel.
 

Mister Luck

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My gas millage has dropped off considerably with my 2016 3500 Bighorn diesel. I used to get over 18 MPG around town and now I am lucky to get 12 MPG. And when I'm pulling my horse trailer with horses I was getting 10 MPG and a recent trip with empty trailer I was lucky to get 6 MPG. Any ideas what to look for before I take it to a shop. This just started. Thanks
How many miles on the OD ?
Are you loosing coolant ?
Are the temps different ?
Cheap fuel or watered down fuel can be problematic.
 
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Watered down fuel? Give me a frikin break! You're nuts
Oh hes not nuts ... last year 3 gas stations here in town were caught with water in the underground storage tanks for all 3 of these gas stations ..... they were shut down, investigated and found out that they were also mixing low and high grade gas together and selling it as premium gas lol ...

All 3 of those gas stations are no longer operating, one of those stations was turned into a waterless car wash and the other 2 were completely torn down ...
 

18CrewDually

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Oh hes not nuts ... last year 3 gas stations here in town were caught with water in the underground storage tanks for all 3 of these gas stations ..... they were shut down, investigated and found out that they were also mixing low and high grade gas together and selling it as premium gas lol ...

All 3 of those gas stations are no longer operating, one of those stations was turned into a waterless car wash and the other 2 were completely torn down ...

Mixing of low grade and high grade at the pump to get mid-grade is how it's done sometimes.

Google it!
What is midgrade gas?
We’ll let you in on a secret: Midgrade fuel doesn’t really exist. In most cases, refineries do not produce a midgrade gasoline blend; instead, the middle-octane option is blended at the fuel pump from a given gas station’s supply of regular and premium gas.

 
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Mixing of low grade and high grade at the pump to get mid-grade is how it's done sometimes.

Google it!
What is midgrade gas?
We’ll let you in on a secret: Midgrade fuel doesn’t really exist. In most cases, refineries do not produce a midgrade gasoline blend; instead, the middle-octane option is blended at the fuel pump from a given gas station’s supply of regular and premium gas.

I'm not talking about mid grade gas , I know exactly what they do .. I am talking about gas that has been mixed with water which is what 3 gas stations out here got shut down for ...

Probably should of looked at why I posted that lol .... just take a look at post #8 and #9 ... I am sure you will "Then" understand why I posted this lol ....
 

Gr8bawana

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Oh hes not nuts ... last year 3 gas stations here in town were caught with water in the underground storage tanks for all 3 of these gas stations ..... they were shut down, investigated and found out that they were also mixing low and high grade gas together and selling it as premium gas lol ...

All 3 of those gas stations are no longer operating, one of those stations was turned into a waterless car wash and the other 2 were completely torn down ...
Hmm...since when is low grade gas and higher grade gas equal watered down gas? It's still gas.
 

Gr8bawana

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I'm not talking about mid grade gas , I know exactly what they do .. I am talking about gas that has been mixed with water which is what 3 gas stations out here got shut down for ...

Probably should of looked at why I posted that lol .... just take a look at post #8 and #9 ... I am sure you will "Then" understand why I posted this lol ....
34jxd0.jpg
 

Mister Luck

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The fact that you still don't get what these 3 gas stations were doing says enough lol ...
Dude never worked for or knew anyone that owned a filling station obviously. There are several ways to get less< than premium.
I realize water separators are standard on diesel’s but there can still be too much moisture present.
Bottle Goggle Jack knows it all I guess.
(Alcohol is a way to supplement water in fuel,
I don’t know how it works with diesel though)
 
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Nickx86

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Check for anything dragging like a seized brake caliber or hub…found out I had a seized brake caliper and my fuel mileage went to ****. At first I thought i was my new tires and change in fuel quality
 

crash68

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Alcohol is a way to supplement water in fuel,
I don’t know how it works with diesel though
You don't want to use alcohol in a modern diesel, it's can be corrosive to metal and your household rubbing alcohol contains water.
To help drive the moisture/water from diesel fuel, there are demulsifiers used for this.
 

18CrewDually

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Cold temps, longer warm ups, short trips, winter blend fuel, idling, not hand calculating, ect. are all contributing factors.
With the frigid temps we're seeing the last week and short trips to the post office or town, mine went from 14.8 to 12.4 for fuel mileage. My first long trip it will recover. Driving cold stop & go around town kills diesel fuel mileage.

Just a follow up on this comment, the truck got down to 11.5 avg mpg on the cluster. When I filled up and hand calculated it was actually 13.5. It was only the last 80 miles it dropped so low on the dash.
What caused it to change? I went from 35 mile one way trips for most of the tank then had a week of 10.6 mile one way commutes. And it got cold. Longer warm ups with shorter drives kills mpgs.
 
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