Mileage down by 10%

welcome!
how many miles on her?

has your driving changed at all? tyres pressure? oil level?

warmer weather/more a/c?

 

Wow, that's a punishing commute.

In addition to bisco's items, you might check the Exhaust Gas Recirculation circuit. It's around your miles it can start to coke up. Quite reliably. There's a pipe between the EGR valve and intake manifold, just one piece of the circuit, but relatively easy to remove for inspection.

 

Time to do some maintenance to the running gear, the brakes may be sticky, the emergency brake cable may be sticky, the bearings may be a bit dry, the tires may be low (air), the 12v battery may be consuming gas (weak) even the interior cabin filter may be clogged, causing more ice intervals.
On my third prius, both the first two lost about 10mpg's between year two and year three.

 

Too many doughnuts?

 

My guess ..... 58 to 60 mpg was not the norm. You were driving more conservatively, and maybe even subconsciously .... hypermiling. Doing so is not as comfortable and is sometimes inconvenient.
52-55 is much more normal. In time you relaxed, and do not make the best effort to maximize fuel efficiency. I agree, weather, tires, weight are all factors as well.

In my G3 .... I was able to get between 65-69 mpg, but it required steady driving at 45 mph, no quick acceleration, no passing, and no stopping. Be grateful for 52-55 mpg ... after all, that is what was promised when you bought the car.

 

You obviously don't have the same tires now as you had the first two summers. What tires are on it now?

 

If they were the same, they should be running more effiently since they would be slicks right?

 

i never pass a dunlin donuts.

 

50 mile R/T in NYC traffic for me. My seven year average (per spreadsheet)? 48 mpg. Started around 52 mpg, lowered a bit over the years. I'm still happy with the car at 100,100 miles and plan to run it for another 100k. (No noticeable oil consumption, btw...)

 

Did the gas stations around you start changing over from E10 to E15 and you didn't notice. I got the shock of my life when I filled up with E10 for the first time and watched my fuel mileage drop like a rock over straight gas.

 

Does it really affect that much? They started adding ethanol to fuel here also and I was thinking perhaps I should try and use the version without it. Thanks for the tip, need to try it with next tank!