MPG dropped in the middle of a trip

The route would contain more inclines, wind, drafting, temperature. No route can be the same

SM-N900P ?

 

Hey DMAX I've been sayin' for a while when I stop for gas on the highway I sometimes see the same step change.
Seems to me the display has multiple steady states (in math lingo) and one day I will get to the bottom of it.
Bottom line it's the real calc of actual gals gas purchased that matters, and that data always seems to suggest the lower MFD value is closer to the truth.

 

red lights do not help at all. My wife drives my kids to school daily and sees lots of red lights. She would average about 40mpg vs close to 50 with highway driving.

SM-N900P ?

 

That's a slight mis-conception you have there.
Coming to a dead stop and then starting up again uses the most energy in ANY vehicle.
That likely was a major factor in the difference that you saw.

 

You did say that the AC was going full blast, right ?
That could be a factor in the ICE running a bit more.

AND has the 12 V battery ever been changed ?
5 years seems to be good life in these models; yours might be 9 or 10.
With the age and mileage, it is possible that your main battery is getting a little weak too.

 

Not likely. I think you are grasping at straws now.
I have ALWAYS noticed a significant drop in the rolling average when I make a pit stop in the middle of a trip.
It doesn't take too many stop/go events to drag it way down.
And if the beginning of the trip was in the morning and then end in the afternoon, the battery efficiency goes down a bit if it gets really hot.
I think you are looking at this backwards and should be REALLY happy that you got over 50 on part of the trip !!!

 

i think you need to set your odo and go for a drive.

 

I think it's the pizza!

j/k There are just so many variables that affect mpg, especially with a car like the Pri. There's probably nothing wrong with the car. It could be windspeed/direction, grade, temperature, a change in driving technique after being on the road a long time, the change in traffic type (red lights), etc.

Stop-and-go traffic usually isn't very efficient, even with a hybrid. There's about a 40% energy loss in the conversion of kinetic energy--regen braking---electrical energy----electric drive in a stop-and-go cycle. That's considerable energy loss compared with being able to maintain speed. The electrical energy from the hybrid system certainly isn't free. It's usually more efficient to use the gasoline engine for acceleration, due to the losses associated with the regen and electric drive.

The decision algorithms of the hybrid system use many variable inputs to decide how to transfer energy, including traction batt state-of-charge, temperature, power demand and speed. The time it takes for the gasoline engine to start after rolling out from a stop is mostly dependent on power demand (how far the pedal is pressed), but there are also other factors. The decision process is very complex and seems inconsistent at first. With enough observation in a variety of driving types, it gets more understandable and predictable (although not entirely so).

Did you switch genres of the music you were listening to part-way through the trip?

 

In my experience, I'd actually say it was the opposite of you've said here. I. e. interstate driving (which should help milage) and red lights (which should hurt)

My only thought is that maybe you did not achieve stage 4 in the engine warm up.

While I've observed a similar phenomenon to what you described, I can't say that I've seen such a marked difference 46 vs 51.

 

Pepperoni?

 

It's hard for us to tell you why from here but the key for me would be what happens to your mpg from here? If it stays below 35, then you have a problem. If it goes back up, then we have to think it was an anomoly.

 

Did the weather change? Strong headwinds or rain? (I've seen my mileage drop from mid-50s to mid-40s in the middle of a trip, just from headwinds.)