Mpg from 45 to 38 to 30 all in two weeks

has it gotten colder? that's one issue, winter gas is another. have you cleaned the egr circuit yet?
sometimes, the plugs are counterfeit, and coils and injectors should be checked as well. maybe throttle body cleaning.

 

How is the 12v battery?

 

If cold and heater on...
Prius will sacrifice economy over driver comfort...
ICE runs to Heat up water for heater

 

Try doing a reset by disconnecting the 12 V battery overnight? Maybe that would help
what do others think?

 

I'm lucky if I average high thirties in the colder months. One, the heater is on so the engine runs more often, second, cold air is denser so you will use slightly more fuel, third have you checked the tire pressures on your car lately? The air pressure will drop on average one pound per ten degrees.

If you check your tire pressure in a garage that's 70 degrees and your car is sitting in 35 degree weather you're going to see your tire pressure drop around 3.5 lbs.

If your 12V is starting to go it will also cause your engine to run more, while it charges up a weak battery.

 

Bare with me for a moment but the last time my mpg dropped that drastically after an oil change the dealer left the oil filter housing access flap clipped in the open position. It's small but it acts like a parachute under your car grabbing air and increasing your drag. Take a peek underneath and try not to curse when you see it.

 

Any update on this? My car is acting pretty similar.

 

Did you take it to a brake shop to look at? Reminds me of my old Sequoia when the brakes locked up.

 

I don’t think it’s the tyres.
The difference between an A rated and a G rated tyre is only a maximum of 7.5%.
Your difference is closer to a 30% reduction.

 

Hello all,
I'm having similar issues with fuel mileage as of late. I have a 2014 Prius 3 with 114K miles.
First of all, I ran the Dr. Prius app and noted that the state of charge on the traction battery rarely goes above the 60 percent range. The 12v battery is about 2 years old. Any ideas from anyone? My mileage rarely goes above 40 mph.
Thanks!

 

Consumer reports found a 34% difference in rolling resistance between the best and worst all season tires. Depending on how fast you drive, that would be anywhere from a 3-17% difference in fuel economy (the faster you drive and/or the more you idle, the less rolling resistance matters). Plus a full depth tire has as much as 20% more rolling resistance than the same tire when worn out so in theory you might have as much as a 50% difference in rolling resistance going from worn out quality LRR tires to cheap new full tread tires. That would be anywhere from a 5-25% difference in fuel economy (25% being the extreme case if you're the sort of driver that pulses & glides between 20 and 40mph).

Additionally, your odometer is wrong when you're on worn out tires. A new 195/65/15 tire might have 12/32" tread depth and an overall diameter for 25.0" When worn to 2/32", that old tire is only 24.375" tall which means it has to turn 2.5% more revolutions per mile. That means your odometer/tripmeter high so you'll think you're getting 2.5% better fuel mileage than you actually are.

Since you're an experienced prius owner from MI, you're probably well aware of the seasonal mpg differences. Since you say you drive a lot, these probably don't effect you as much since most of the winter fuel economy drop happens from warming up the car (the more you drive per warmup, the less that "wasted" fuel matters toward your average).

So that leaves the brakes as a likely cause of much of your lost mpg. Did they clean and lubricate your slide pins? Did they replace or resurface your brake rotor? Both can contribute to brakes sticking/dragging. Many disc brake-equipped cars come with pad return springs, but the prius is not one of them. It should be possible to retrofit some, but it'd be custom.

 

Your prius will try to maintain a ~60% charge - that is totally normal.

 

Summer tires are always better on grip, handling, rolling resistance, and comfort than all seasons tires. But only for summer or states with no snow. The wear is often worse than most USA spec all seasons tires.
MPG drop is often caused by the owner behaviours not the car. If we drive in state roads at 50-65 mph, anyone can get at least 45-50 mpg in relatively flat roads. In city, it could be from 35-60 mpg, depends on how the traffict and technique. I often can get more than 60 mpg on state roads at 40-50 mph.

 

Do this reset.

 

Have you tried this? How much of a difference in the steering did it make for you? I’m wanting to do it because I feel my car needs just a minor adjustment that an alignment did not fix fully.

 

Yes. It fixed my wandering issue on the highway where I used to always correct the steering wheel like its going left and right back and forth. Try it. Its a harmless reset. I've also gained better MPG for some reason. It must have reset the ECU as well.