New 2014 Prius MPG Problem- Help me figure out what Im doing wrong!

That's about the time refineries start switching to winter blend gas, which will get worse MPG.

 

Welcome to the forum.

Check tire pressures.
Drive slower (your comment about doing 75 on the Interstate)
Don't use premium fuel
Check the prevailing winds (that is only partly tongue in cheek)
Get the 12 V battery checked.

Don't worry about it. If something serious is really wrong, it will get MUCH worse.

 

You're right in the ballpark for such driving. High speeds, short trips and winter weather are all bad for fuel economy. Mix a couple of those together and it gets worse.

 

Bob Wilson

 

I'm only about two hrs away from you and the weather has changed quite a bit. I don't think anything is wrong with your Prius, look at my fuelly and you will see my MPG history. It's not broken down into percentage of Hwy vs City, but a lot of my fillups are a mix of both or mainly highway. I drive around 75-85 mph on I-95, I-75, and I-20.

 

Many years ago, Jason's GreenHybrid mileage database included temperature. So I gathered a bunch of individual records to generate these charts:

This is my first Prius record showing the correlation between temperature and MPG. The 'trend lines' are a math trick to reduce the samples to something that approximates a smooth function.

I have never understood the dip at 70F with local peaks on either side. Just to make sure, I also plotted the first standard deviations on each side of the mean:

The only independent variable is the driver . . . but then I've never understood him as he is me. The 70F dip was not found in other driver/car records:


Here is another driver and vehicle. Curious dip around 40F which corresponds to an impression I've gained that below 50F, the temperature effects are more pronounced.

Her we see the significant dip at 50F, a third Prius and driver.

So I took just my Prius metrics and interpolated the temperatures between samples. In effect, increasing the temperature 'resolution' by doing an approximation. My preferred technique is Gaussian using:

• 25% prior temperature
• 50% current temperature
• 25% following temperature

This technique eliminated the 70F anomaly and avoids what might have been a sampling error:


So I'm fairly confident that the MPG drop-off under 50F is accurate. Later, I had occasion to do a 24 hour round trip from Huntsville AL to Columbia SC in the winter.

This trip was under a stalled, Arctic high pressure dome centered midway near Atlanta. The temperature ranged from 17F at the start; 38F at the Interstate entrance around 3:00 PM on the way back and ended at 19F. No significant wind, the trip was on cruise control the whole way. I found the 2 hour measured, MPG followed the air density that varied by outside air temperature. In effect, the MPG was air density driven below 40F.

The primary temperature effects I have observed are:

• cold-start warm-up - this is the primary effect urban, short trips
• air-density - this is the primary highway experience

I do not discount winter blend effects nor tire rolling resistance. Rather, I don't have any metrics.

Bob Wilson

 

I would check your tire pressure.

I generally get 52 to 54MPG, but I religiously keep the cold tire pressure set at 42PSI (Front) and 40PSI(Rear). Keeping your tire pressure high will change your overall MPG. I do not trust the dealership mechanics and/or tire shop people to set my tire pressure, there are too many inconsistencies. Get yourself a good tire pressure gauge (not a cheap pencil air pressure gauge) and check cold tire pressure at least once a month, especially when there is a change in temperature and/or barometric change.

 

Good advice above. I would add that it's often detrimental to keep the HSI in the EV half; when accelerating, you want it to be towards the right, and even going a little bit into the PWR bar isn't a terrible thing. Once you're at speed, it's up to you whether you want to be in the "just drive it" camp, or if you want to dip into the hypermiler category. I would recommend just driving it, the car is pretty smart about what it does.

If you accelerate too slowly, using too much battery power, you end up paying for it later; you get 100 mpg now, but you get much less later when the gas engine has to replace the battery power you've used. In the Prius, all the energy you use eventually can be traced back to running the gas engine. Using battery power means that you ran the engine, recovered some of it in the battery (losing a percentage to inefficiency in energy conversion), then used it from the battery (losing another percentage). So it's best to only use battery power if you'd be using the gas engine very inefficiently - like tooling around a parking lot, or maintaining your speed on a slight downgrade.

 

once in a while, a new prius comes with a bad 12 volt. get it checked while you're still under warranty.

 

Winter blend gasoline will drop you mpg's on your Prius about 10%. Even when winter temps were for a while were near 60 F , mpg's was still way lower than summer with the same temp, road condition etc. Right now mpg's 46 calculated, summer 52 mpg calculated.

 

Leave 5-10 min's early and set cc at 60 mph.... Relax and enjoy the less stressful drive which will also include significantly better mpg compared to 75 mph

And yeah, all the above, tire pressure (I run 44/42 on my persona)...etc.... Cold weather really kills our mpg, it's a fact.

 

I am off 4-6 mpg since it has gotten cold here, myself. The wonderful news is that gas is below $2.00 now, so less concern for me. I am also driving a little faster, and 46-48 mpg at $1.75 per gallon ain't bad to me. Trust me-- this cold has taken a toll on all of us.

 

i hope the o/p survived the new year.

 

I agree but not so large...I would say winter blend is maybe 2-3% less MPG.
I am expecting about 10% MPG difference is the biggest fuel delta we might ever see between a high energy E0 and low energy winter E10.
I definitely agree winter MPG is at least 10 maybe 20% lower, but it's due to many factors including thicker lubes, high tire rolling resistance, cooler engine, as well as winter fuel.

 

I agree, there's a significant dip in mileage with colder weather. I put most of that on the thickening of lubricants. Short trips don't seem to reduce fuel economy in my opinion; I find the opposite in fact. Highway miles, when driving at 70 mph or more are less-efficient than city miles in most cases. I don't think changing tire pressures or changing your oil will have much of an effect, unless you're using a 30 or 40-grade oil.

 

Longer trips at lowish speeds are where I get best mpg, year 'round. I do think short trips cut into mpg more so in winter: your warm-ups are more protracted. The car looks at the lower ambient temperature and changes warm up behaviour accordingly. Strategies that work for me:

1. Drive less. No kidding, this is hands-down the best way to save gas, lol.
2. Consolidate errands. May not be possible, depends on your circumstances.
3. Choose secondary, lower speed routes. Higher speeds kill mpg in an exponentially increasing manner.
4. Avoid hills. It is sometimes possible: a little tweaking of your route can avoid climbing and descending a local bump.

 

Or ride a bike. LOL

 

Well, we walk for local errands, as long we're not gonna be pack horses. Of late, semi-retired, the car get's fired up maybe every other day. Sometimes goes 3~4 days.

 

Just came to the forum for this very question. 2014 Prius 4 and was averaging 48-50 mpg in summer, and now around 42 Mpg. The change with winter fuel makes total sense. I am also going to increase my tire pressures to 42/40. Hopefully that helps.