Problems after Pip left running for a day

Instant mileage or mileage since last fill?
If left running for a day, I am sure the ICE ran for part of that time, using gas. Gas used during that time generated no distance. So if it used 1 gallon your first mile of driving would give you 1mpg. Very simplistic example just to show the general idea.
But this is just a very wild guess.

 

+1 Yes Your ICE was running on and off all day long!

 

between dad using the car, and leaving it on all day, the mpg's should be messed up. refill and start over, i'm sure you're fine. all the best!

 

+1 Yes Your good to go! Enjoy!

 

You might try rebooting, remove neg lead on 12V for 5-10 seconds. This wu\ill give you a fresh start.

 

I 2nd the reboot via the battery disconnect as well if it continues.

 

I wouldn't bother with the rebooting. Thats a waste of time in my opinion. It doesn't change your car. It just puts zeros where there once were numbers. If there is something wrong with the car, something will still be wrong.

You don't have enough information yet to say something bad happened. Get a new tank of gas and reset the trip meter.

 

+1 I agree! I think most of us think nothing is wrong at all. The car need to start from time to time to recharge the battery and then would just sit until it need to charge again. It did this until you picked it up from your dad. Thus it used a little gas every time it ran, which is why your mileage is down. Your mileage will come back, don't worry it's just fine!

 

I ran my Prius c for 54 hours straight following Hurricane Sandy, with no ill effects except for the hit on my mileage for that tank.

 

Like has already been stated, the engine will just run from time to time.

No harm done.

MPG for that tank will just be really low, since the engine ran frequently without any travel.

 

I don't drive one, but for the instantaneous mpg I would say coincidence.
I, and others, most likely could give you a better guess with more info.
Altitude change?
Did you check tire pressure?
Different speed than normal?
SOC at start?

 

not sure what you mean by 'mileage for the trip on the highway'? you would have to reset a trip meter to know that.

 

There should be no problem. Right now we don't know if there is an actual problem or just a perceived problem. Best advise would be to fill up again and start over. If by the next tank you are still low, then there is something worth checking. The same road different directions can give 30mpg+ difference even when it looks flat. My interstate highway southbound nets me 80mpg to 99mpg at 75mph. It looks pretty flat, but there is a small elevation drop. The same way up at 75mph nets 35mpg to 50mpg. Temperature has an effect especially with tires and cabin heat. Wind at any given moment can have a huge swing in mpg. The point is that 1 data sample of 1 drive on a well known road is just that, 1 data sample. There are so many unrecorded variations that it is impossible to relate this 1 data point to all the other data points and reach a conclusion worth anything. You need lots of data points to "cancel out" the variations or at least keep them quasi-consistent so you can compare apples to apples.

Leaving a Prius on for a day, idling even, is no problem. I have taken 30+ hour driving trips where the engine is running 99% of the time at high revs 75mph to 100mph with the only stops being for gas. Using them as a generator (mine is right now actually) is common.

Report back in a few weeks with what your average fuel economy is.

 

what was your battery charge level during the trip? was it extra cold that day? Battery should have been recharged after a few miles of driving. plug it in again and see if you still get in the 30s mpg. was there a strong head wind perhaps? Did he get the tires filled with air at 35 psi and maybe you run them higher? lots of unknowns.

 

Is it possible long term fuel trim levels could get thrown off?
How long does it take an average ECM to correct long term fuel levels if there is a correction?

 

Your car shouldn't really run any different idling then at speed unless you have some big clog in your intake? This is not my forte, I generally stay on the electrical side. But with the same octane gas, idling so presumably staying at the same elevation, it should roughly be the same.

 

Did he fill it up with E85?