weird rear tire wear fixed and now low mpg

Found a great deal of unusual rear tire wear that would eventually cook several spots down to the tire cord after around 10,000 miles on my wife's 05 Prius. Did not rotate to try to find out which corner was causing flat spotting. Did get a rebalance and alignment to make sure these were not the problem.

I found the rear passenger side wheel was not rotating smoothly. I was taking the wheels off to clean bits of tar that had accumulated on the inside portion of the wheels before a tire change late this summer, and felt the snag as I manually rotated the wheel. The drivers side was fine and turned smoothly. The snag was very smooth so I didn't think that the bearings were involved and it always occurred at the same point in the rotation for a few degrees of the wheel/hub movement.

So, off to the dealership to investigate. They found that the rear brake was snagging just enough during rotation to induce the severe tire wear. This was fixed. Put new tires on all corners to get rid of the flat spot noise, the third set so far in a little over 50,000 miles. Everything went back to normal. Nice quiet round tires again!

About a month later, the mileage plummets from 50 to 54 mpg down to 38 to 39. No major changes, tires and pressure, gasoline, driving style or routine. Winter fuel only knocks mileage down to around 50 mph. And then noticed that the ICE does not shut off like it should. It's the ICE not shutting off that has me concerned. What might be going on? Any ideas?

 

I would love to think it's just cold weather related, but with temperatures in the 50s and 60s a couple of weeks back... I would hate to see my mileage figures when we get down into the single numbers and teens during winter.

This low mileage event has spanned two full tanks of gas, and mostly in very nice weather. The lowest "winter" mileage figures we have seen from this car so far was 48 mpg last year. Temperatures were really cold when that was measured.

 

Good ideas. I'll get the car up off the ground and check the two rear wheels for binding by rotating them again. Will also check the temp setting. Wife has the car... so will do the checks when she gets home tonight.

Thanks. The mileage on the info screen this morning when she left was 39 and it really took me by surprise. This is still a great site!

 

Thanks for the responces and ideas/help given... so I had to try something and here's what I did last night as an update.

Went to Thankgiving diner about 40 miles away. Took wife and her Prius, plus several dishes of food. Reset mpg at start. Noted temp was 39 degrees F, dry road surface, little wind. Set heat at max cool and lowest fan, outside air. Course is rolling, downhill... elevation change from 700 feet MSL to around 100-150 feet MSL. Back roads, no Interstate at 40 to 50 mph mostly. No cruise control.

Got there with indicated 56.3 mpg. Return trip was via slightly different route... climbing back to 700 feet. Outside air temp had dropped to 27 degrees F, so put a tad more heat on to 69, still at lowest fan position. Mileage for entire trip ended up at 51.9. Only 80 miles, but a fairly representative Maine drive.

When I first got into the car (wife drives it 99% of time) found heat set to 74 degrees and at mid fan position. Soooo, might just be an inattentive driver too lightly dressed for the season induced mileage drop to 38 to 40 mpg type of issue? I have a tough time thinking that a 5 to 10 degree heat difference would make that much of an impact on mileage. I'll have to keep better track for a while.

I'm still going to check that rear right wheel for the brake drag as soon as I get a chance to put the jack under it. Don't want to flat spot the new tires.