Not another sudden bad mileage thread?

welcome! sounds like you may have to break down the wheel/axle to see if anything is damaged or bent. put it on a lift and free wheel it to see if there's any binding.

 

traction battery dying, cold temp causing the motor to run more, low tire pressure, wrong tires type, brake dragging from impact,the car just hates you for wrecking it. dead fat woman in the trunk or a combo of all of the above.

 

maybe the body shoppe killed your 12 volt.

 

What specific tires are on the car then?

 

new tyres will have a larger diameter, affecting the readout. not sure if higher or lower. one revolution would cover more ground. the computer uses revolutions to figure mpg, and distance. so you're going farther than the car tracks?

 

Standard size tire for a Gen 2 Prius is 185/65/15. Wrong size or typo?

 

Yeah if you go from a totally worn tire to brand new, the same tire/size, the car will now think you've gone less distance, due to larger diameter, less revolutions. But it's not a big difference, and even less if the old tires are just half-worn.

The tires are likely part of it, maybe deteriorating weather (though OP says the drop was immediate).

As mentioned above, maybe that curb hit had hidden consequences.

We can rule out fat dead women in trunk: there is no trunk.

 

maybe it was just a coincidence, and you're going to have to look at major items like the hybrid battery.

 

Time to start maintaining the hybrid battery. It's easy to wait until it is too late, but it will cost a lot more in the long run

 

A set of poor rolling resistance tires can easily account for about 5 or 6 mpg loss, so presumably just the two tires can account for half of that. Then factor in the change to winter gasoline and there's another couple of mpg lost. It could be a combination of factors like that.

 

Turn your cabin heater off. I have found that I lose No (Zero) MPG between driving in summer and in winter so far by just not running my cabin heat. I set the temp control to MAX and the circulation to external, but turn off the climate control/blower motor. As long as the computer is not actively managing the interior cabin temp using the gas engine, the latent heat being forced though the heater core into your defroster vents will keep the cabin temp reasonably warm and windshield defogged. I might hit the blower motor when I'm on the road and the engine is already running for a quick shot of hot air, but other than that, I need nothing.

My tires are all at about 35 psi, and I have regular standard tires on my car, no special types. With those I get about 45-48MPG and I drive under terrible conditions. 40psi+ seems a bit excessive and probably isn't safe. Leads to tire bounce and less handling traction, also excessive tire stress.

Probably the biggest winter impediment to good gas milage is snow covering on the road. Even a mild crusty covering raises your rolling friction and can have immediate day to day differences to your milage figures. Was there snow coverage on the road since your accident?

Oddly enough, I've found the winter gas blend issue to be non-existent to me since I bought my Prius.

Check your E-brake cable tension, although, if that's tight, you would probably be smelling it while waiting at intersections.

Look under your car, and smell around if you might have a gasoline leak. Do it while the car is running in your driveway for awhile and the fuel system is pressurized.

Lastly, check your coil packs and iridiums. Who knows if a knock could put something out of whack that was marginal to begin with.
Going from 4 cylinders to 3 would kill your gas milage, and I've seen some people driving Toyotas around on three without even knowing it for awhile they are so smooth.

Is it possible that your milage computer is simply mis-reporting your milage because of the different tire size? Have you done the fill-milage calculations at the pump?

Just some new ideas, hope this helps.