Dramatic lost of MPG and then all of a sudden back to normal

Very hard to know without more info, but that difference is probably small enough to be accounted for by differences in weather conditions and aircond usage.

 

Maybe a bad tank of gas? Did you happen to fill up before mileage returned to normal?

 

I would have to say, we need a clearer definition of what is happening here.

I don't know what you mean by Dealer test drove it, put on computer. Do you mean it was checked for codes or problems at the dealership?

If the dealership is giving it a clean bill of health...

Then my next question is what is your OVERALL MPG per tank? Not trip to trip.

Because I have found that my trip to trip can vary greatly. On a nice weather day, I can take a trip mostly dominated by side streets and end the trip with a ridiculously high (but great) MPG reading. I've turned the Prius off, and because the trip was mostly dominated by battery travel had MPG ratings in the 80's and 90's.

I've also found that if I'm doing a short trip without The Prius having been warmed up and/or when the battery is low, I can end the trip with a MPG rating in the 20's.

I don't worry about either MPG reading. What I watch is what my MPG per tank is doing.

Then my final question....You only have 2 posts on Prius Chat...so are you new to ownership? Or have you owned this vehicle a long, long time and thus KNOW this behavior isn't normal?

Because rather extreme variations in MPG from trip to trip can happen, that can be normal. If you are finding your MPG dropping drastically on a tank per tank basis....then you might want to start going through the steps of checking everything from tire pressure to your 12 volt battery.

 

With any electrical or other weird issues with the Prius, always suspect the 12V battery until that possibility is eliminated. Get the voltages with the method in this thread and report them back here just to eliminate this as a cause. Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

The procedure works using just the parking lights instead of the headlights.

 

Without knowing the full history, it is hit or miss what the real answer is. The OP is not giving sufficient information to help evaluate if there is a problem.

Remember the Gen II has the infamous bladder, therefore the MPG will vary. What really matters is overall mileage over "several" tanks of fuel.

It would help if the OP would fill out the questionnaire that is linked below.

Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat

Ron

 

Could the dealer have disconnected the 12 volt battery while working on the car?