Gas mileage variable

I have a 2012 Ram 1500/hemi. I am not sure where to approach researching this. During the winter months both city and highway mileage were low as to be expected(12-15 mpg) a lot of the time below 20º F , auto 4 WD, snow on roads, & studded tires). Now, the temps are a little warmer and less snow on the road - on a recent highway type trip - now, 17-19 mpg are indicated (and gas guage corresponds correctly) and it seems more time in the ECN mode than before. Driving style and routes are 'normal', but I am not sure why MPG has improved. Any ideas as to why this would happen. Note: I am reading and learning about the MDS system but haven't done anything to modify, etc).

Sounds perfectly normal to me, my 2016 gets better mileage in warm weather than cold. Warm weather means less time with mixture enriched after startup, less viscosity drag on moving parts, etc.

Best,
RI

Yea. Winter blend fuel doesn't help.

I guess it's all the ethanol in winter gas. It has less energy per gallon, so you're a little deeper into the throttle at any given speed.

I guess it's the states version of being more green, or maybe to help subsidize farmers.

It's probably normal, but here is a test you can do if you (or someone you know) has a scan tool which can give 'real-time' computer readings:

Test 1: Plug scanner in. Read engine coolant temp when the truck is cold, not started (like in the morning). The engine temp should match ambient outside air temp. Or be real close.

Test 2: When the truck is up to operating temperature, read the computer's coolant temp via the scan tool. Verify actual engine coolant temp with an infra-red temp gun pointed at the metal part where the upper radiator hose is...on the engine (the metal part ..not the rubber hose). That's where your coolant leaves the engine ...to the radiator. Bear in mind not all IR temp guns may be calibrated the same, so a couple deg difference will be ok.

Test 3: Also read/verify the outdoor temperature sensor reading.

If the temperatures you get from the tests above are off quite a bit, then the temperature sensor could be faulty, which would likely affect your truck's air/fuel mixture, esp during extreme hot and cold temps. Normally, if they are off a fair amount the engine might also 'miss' or stumble too, which you aren't seeing. Also check out the MAF reading too. There are some videos how to verify engine and outdoor engine temps.

Also, might be worth removing the engine rubber air tube (snorkel) from the air filter, inspect the throttle blade and surrounding area for fuel deposit build-ups. It only takes a very small amount to affect idle conditions, which can suck more fuel during idle. It's a normal maintenance procedure. Clean with a throttle-body cleaner (spray) and a solvent-safe plastic brush.

All the above reasons, plus colder intake air requires more fuel to operate at the same power level.
Back in the day a "choke" on the carburetor was used to get more fuel into the motor when cold to get it to run. Today electronics do that.

You state the "low" mileage was city and highway, then state you got higher mileage on a "recent highway drive". I would suspect a large portion of the difference is just where and how you drove. For example my round trip to work everyday is 56 miles in my work car. 24 miles 70+ mph freeway, 22 miles 50-55 mph 2 lane, and 10 miles stop and go in smaller towns. Now if I do a long freeway trip the car will get 25-30% better fuel economy versus the mixed driving on my normal trip to work. That is about what you are seeing in those numbers.
Of course you mention many other factors that could increase fuel mileage:
- warmer temps (do you ever remote start your truck, or simply let it sit and idle to warm up when it's cold?)
- the switch between winter and summer grade fuel can cause a small difference.......but don't think they go back to summer blend until May???
- snow generally causes a little more drag and reduces mileage
- obviously running in 4wd will cause an issue

Switching tires changed a lot. Factory tires had real good gas mileage 21mpg. All terrain tires had a good impact. Trucks vary more from summer to winter vs what cars vary.

Switching to tow mirrors had an impact on mpg.

If you can find a no ethanol station near you, you can try that in the colder months and will see a bump in mileage.

How old/new is the air filter?

Could there be a rodent nest under the air filter getting sucked 'up' and reducing airflow ...at higher RPM road speeds? (rodents tend to move in, in the fall/winter).

I've had that happen a few times on my plow truck which I don't drive much in the summer. Check out the simple things first. But yeah, vehicles don't always get as good of MPG in the cold...for sure. Plus people tend to idle their vehicles more ...and you get zero mileage when the truck isn't moving. Plus they tend to run richer in the very cold.

TalkeetnaDodge said:

I have a 2012 Ram 1500/hemi. I am not sure where to approach researching this. During the winter months both city and highway mileage were low as to be expected(12-15 mpg) a lot of the time below 20º F , auto 4 WD, snow on roads, & studded tires). Now, the temps are a little warmer and less snow on the road - on a recent highway type trip - now, 17-19 mpg are indicated (and gas guage corresponds correctly) and it seems more time in the ECN mode than before. Driving style and routes are 'normal', but I am not sure why MPG has improved. Any ideas as to why this would happen. Note: I am reading and learning about the MDS system but haven't done anything to modify, etc).

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For every 10 degree Fahrenheit drop in ambient temperature, the vehicle tire pressure will drop about 1 psi. In much colder weather, vehicle tires will become under inflated (unless the driver inflates the tires) - causing a drop in fuel mileage.

When the weather warms, the tire pressure will increase 1 psi for every 10 degree Fahrenheit increase in ambient temperature.

Is it possible you didn’t add air to your vehicle tires as the ambient air temperature dropped, causing an under inflation issue with the tires?

Ken226 said:

Yea. Winter blend fuel doesn't help.

I guess it's all the ethanol in winter gas. It has less energy per gallon, so you're a little deeper into the throttle at any given speed.

I guess it's the states version of being more green, or maybe to help subsidize farmer

Click to expand...

It's the equivalent of putting tobacco in ones green smokes
Does nothing but pollute the richness and purity of the main ingredient!

Rubber and lube's get a lot stiffer in the cold. Increases tire rolling resistance. Putting 10ply tires on a vehicle also increases rolling resistance...decreases economy. If a guy had 10ply in the cold, that's a double-whammy.

As you can see, lot off possible reasons.

Thanks for replies. Aware of tire pressure, etc Need to research fuel better ( I used a different station) I wasn’t sure if there isn’t something ‘sticky’ in switches/computer - I am still learning about vehicle

Racer9 said:

All the above reasons, plus colder intake air requires more fuel to operate at the same power level.
Back in the day a "choke" on the carburetor was used to get more fuel into the motor when cold to get it to run. Today electronics do that.

Click to expand...

Colder air is more dense, meaning more mass of oxygen per volume of air. The ECU compensates for denser air by adding fuel to correct the stoichiometric ratio. The stoichiometric ratio is maintained, regardless of air mass. What this means for performance and fuel economy is that, since the air is more dense, the engine draws in more air mass at lower RPM then the ECU adds more fuel then the engine makes the same power with that mass of air and fuel as it would in warmer conditions at a higher RPM. The same mass of air and fuel has the same potential energy.

When you are driving on snow and ice, your wheels are slipping, using more energy per mile.

Is there really that much difference in fuel? Chances are all the stations are getting fuel from the major gasoline depot in your area.

I used to work next to the fuel depot that serves our area (Yeah we had to evacuate our building a few times when people smelled gas!). That depot serves all the gas stations in the entire region wider region in our part of the state. Semi tanker gas trucks come in of all different brands. As far as what I've heard/read... the gas delivery driver (truck driver) just adds in their quart can of 'Dr. Good' (Shell, BP, Others) at the station upon delivery. So we're getting essentially the same gasoline out of the same big holding tanks, weather I go to station X or station Y, or station Z a few towns over (regardless if they're Top Tier or not)

That's how it's been explained to me. Texaco isn't sending a convoy of semi's up from Texas to serve the local Texaco stations, and Exxon isn't shipping a convoy of semi's with gasoline...from CA for Exxon stations. And our local, regional gasoline stations doesn't have their own refinery in the back-40 here. They're all taking out of the main big holding tank next to my old workplace. And I doubt all the companies are each sending tankers of THEIR GASOLINE up to Tx. They'd each go broke.

So going to the next station down the street won't necessarily mean different or better gasoline/diesel. And are the so-called quart of additives the driver adds to the entire fill-up for the station, REALLY making a notable difference? Or just making me 'feel better'? Maybe both?? IDK

Maybe trying non ethanol fuel a few times next winter and hand-track your economy and see if that helps.

Jeepwalker said:

Is there really that much difference in fuel? Chances are all the stations are getting fuel from the major gasoline depot in your area.

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Yes there is a difference. They order it with varying amounts of ethanol, ranging from zero to 10%. Newer holding tanks at the station have stricter leakage/water percentage allowances.

Jeepwalker said:

So we're getting essentially the same gasoline out of the same big holding tanks, weather I go to station X or station Y, or station Z a few towns over (regardless if they're Top Tier or not)

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Top Tier is still in shortage in some areas, my local Sinclair still isn't able to get it. It's also normally mixed into the tanker at the depot/refinery.

Jeepwalker said:

Maybe trying non ethanol fuel a few times next winter and hand-track your economy and see if that helps.

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If a station sells an ethanol free option, the blends will have less ethanol. Sinclair where I live has ethanol free premium, and another station has ethanol free regular. I always run mid, and can tell the difference if I'm on a road trip and get "full strength" ethanol, usually around 2mpg less as reported by the computer. I didn't notice much change going to ethanol free premium, and definitely not enough to cover the cost difference. It should also be noted that my truck has a mild tune, but still has the mds system.

I say all of the above also..fuel types/blends being the most influential to me.

Winter fuel along with the alcohol mix has a higher Reid Vapour Pressure in winter fuel to make it easier to ignite. Used to see some problems with driveability in the spring and fall when folks fueled up at low volume gas stations.