Sudden drop in mpg

There was a thread recently on this - it could be worth perusing it:
Sudden drop in life-of-vehicle mileage | PriusChat

 

Is there a possibility that either this tank or the last wasn't filled completely? I've occasionally had a pump which cut off early, really messing not just that tank's l/100km figure, but the next tank as well.

 

I've not taken a lot of notice of the display - I compute each tank on a spreadsheet as well as in FUELLY. My early observations with the display was that it is optimistic, but between 4 and 10%. It's not a precision instrument - it does a computation of fuel flow, makes an assumption that the last fill was a full fill (to the first click-off of the pump as per the manual) - none of those figures are measured with great accuracy, but it does a reasonable job for what it does. A bit like most cars - I've not had on which doesn't read optimistically.

Do you reset TRIP A (or B) when you fill?

 

The Manual is great - take it to bed to read - it'll have you asleep quickly . Seriously - it's not the best manual I've read, but has lots of useful information.

If you're using the digital display for fuel monitoring, probably the best way is to RESET Trip A (or B) when you refill. That way you can see a computed average for the current tank.

If you have this display , it is just recording the economy for your current trip - since last time you started the car.

If you select TRIP A (or B) now, it will show you the car's average since they were reset. Similarly if you put it on ODO - that will be a lifetime fuel economy.

The other display you can put up is this one:

This was last year, the last time I photographed - and those l/100km are better than I normally get, was on a short 4 day trip.

Those 4 daily figures are a computed average of all the trips I did on those 4 days - and you can scroll down for a couple of months too.

 

There are many things that can affect fuel economy too. The weather in particular...

Temperature affects how hard the Aircon needs to work, how much drag you get from your open or closed windows, the viscosity of lubricants, the rolling resistance of your tyres, how long your engine needs to stay on at the start of your journey while it warms up. Wind speed will work for or against you, depending on its direction. Air pressure affects drag, cooling, and combustion. Humidity affects combustion.

It might be worth checking your tyre pressures, as if any are getting low that will impact fuel economy.

Pixel 2 ?

 

58 down to 49? I had it happen to me too. I never use that big screen. I only use the Trip-A odometer numbers. Much more simple, and real time.

 

probably air conditioning. not knowing where you live, it could be hot, or not.

 

Just some "usual suspects":

1. Change in the nature of your trips? Factors like higher speed driving, excessive idling, short trips, stuff like that.

2. Increased use of of AC? (aforementioned by @bisco)

3. Recent maintenance?

If you're running higher tire pressures: dealership tend to drop them back to spec, unrequested. (Check pressures with the tires cold, see if they've changed.)

Oil change with heavier weight, and/or overfilled. (Overfill you can check, on the dipstick.)

Messed-up brake inspection resulting in brake drag. (Feel all wheels after a drive, see if any are unusually hot.)

4. Load change? For example, it used to be just you in the car, but you've started carpooling. Or transporting bricks for the patio, stuff like that.

 

and previous to me 'the professor'.

 

Maybe the fob was left in the car before you bought it, so the health of the HV never was 100% Check the 12V and the HV. Anything else is supposition.

 

I wonder if the computer has a glitch sometimes? Mine dropped by almost 10 mpg a few months ago. And now everything is back to normal. My AC is always on, to help cool the traction battery and ME, so it's not that.

I found that if I run the tank all the way down to just one blip remaining (drive 600 miles) then refil, my mpg number calculates to be higher than if I was to refil at half a tank. Weird. (I only look at the Trip A real-time numbers.) I also went back to Eco mode, and the numbers shot up.

 

It does help a lot if we know your location. Personally I never worry about trip mileage, it’s too variable. Does the 2016 have lifetime average mpg? If so Keep in mind that that figure is really Mpge, it all is.

There is something like 18 different computers on board and it’s possible they are all attempting to reboot.

Just like our computers, they can all develop glitches and then mysteriously reboot to normal.

 

Yes, the 2016 has a "lifetime" average mpg. Right there with the odometer. Somebody said it resets itself after 10,000 miles? I've reset it a few times manually when refueling, just to see what would happen. After a short time it jumps back up to the lifetime number... which is 57.6 for me.

I hand calculate my mpg numbers. The Trip-A display is off by about 3 or 4 mpg.

 

Right now mine is at 160mpg. I’m not sure it makes sense to reset as it’s the most reliable figure.
If you reset you’re starting all over again.

I rely on the computer and assume my hand calculate is erroneous. This is because, one can never fill the car the same. 1/10 of a gal, changes the math!

 

I've monitored hybrid battery temperatures, with and without AC, on a hot day, and saw little or no difference.

Constant AC use does impact mpg, 5~10 percent in my limited observation.

Also, constant AC use makes for a mold/mildew breeding ground. At the least, turn off AC (but keep the fan running) for the last 10 minutes or so of your journey, whenever practical.

I would argue for the opposite case. Any (slight) vagaries in the level of fullness at one refuelling, will virtually balance out with the next. The car's displays, otoh, are invariably optimistic, 7.5% in my third gen experience, and as far as I know, are lost if you ever disconnect the battery.

 

The gasoline gauge and float mechanism are extremely non-linear, they cannot be depended upon. It’s called a gauge so you can gauge what it’s doing. Otherwise it would be called an INSTRUMENT. If one were to compare a micrometer to a fuel gauge, the micrometer would win by a landslide.