MPG Dropped to the mid 30s

2011 Prius bought new (11/11) for wife's 45 mile commute from south of Dallas, through the city and north. Mileage has always been upper 40s to low 50s until the last week or so, now she is seeing 35 mpg displayed.

I have asked for a check at fill up. I just pulled the car out to wash it and noticed the engine came on right away, same when I put it back into the garage. In the past we would get part way down the driveway before the engine came on. Just got the recall notice for the software update but never saw any warning lights. Also did a code check and no codes found


- Have you read Yet? Yes

- What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations) 46-52 display and tank fill up calcs.

- What fuel economy are you expecting and why? 45+ past experience

- What are the approximate outside air temps? 40s am 70s pm

- How long are your trips? 45 miles

How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? original ~28 months

Have you had your alignment checked? Any pulling or abnormal tire wear? Yes - No

- How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving? A mix that hasn't changed, some stop and go in the evening, mornings 20s-70s

- What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.) no steep hills, first 20 minutes residential 40-50, remainder multi lane 60-70 mixed with rush hour congestion.

- What are your tire pressures? 40 all, no change since new

- Is your oil overfilled? (i.e. above the full mark on the dipstick) no

- Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.) BMW 330 3L, six cylinder, auto 22-24mpg

- What region/state are you in? (if you haven't set your location) Dallas

- How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking? Drive like any other car.

- What modes are you using, if any? "normal", EV, power, eco? normal

- Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on? no

- Are you driving using D or B mode? D

- HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to? AC 74 Heat 68

- Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15). Factory tires and wheels

- If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute?
No known changes.

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Thanks for the help​

 

57,000 miles, air filter changed 5,000 miles ago. Battery vent, is that the one going to the rear storage well? 12V Battery in rear shows 12.52V. Sat all day Saturday and just out and back in the garage today.

No erratic displays or anything else to raise a question.

Thanks for the suggestions.

 

My wife just started the Prius, hit the EV button, and got a message saying EV currently not available.
ECO and Power buttons turn that name in green in the display.

 

Hasn't been for the last 2+ years. Always been able to start and move the car 20-30 feet before the gas engine starts. Even early morning with the headlights on.

 

Not sure of the SOC, is that shown on the display? 12V battery looks new, no corrosion on the terminals, and had a 12.52V charge yesterday. It is due for an oil change and I will try to have the dealer do that, software recall, and check the mileage situation this week. Yes, the oil change is a pain, but I have settled on ramps with 2x6s to lessen the angle and clear the bumper cover. The BMW needs the same.

This morning's commute began with the engine on immediately. Later, in some stop and go traffic, the gas engine did shut off and would stay off until ~17mph. 0600 temp 55F.

I will more the Scan gauge from the Tacoma to the Prius and see what it shows. Am I looking for anything special other than mileage?

Thanks for the information.

 

Visited the dealer who said $55 to diagnose low mileage. Couldn't find a problem and waived the $55. Now to see waht a series of tank calculations show.