2007 Low MPG -- Can't figure out why

I have noticed as well this kind of thing rarely seems to get resolved from all the googling and forum posts I have read, but (and this may sound unreal) I had my Prius in the shop at Mellors Automotive at the very time of the inquiry I posted above. Just got it back home. He had it for over a week and kept telling me nothing was wrong, but I got a surprise and the end after I picked it up.

This is the whole story:

I bought the car with 109,000 miles on it in September 2011 and it ran fine and I always averaged usually, 46 - 50 MPG and my personal best was 52 MPG done on paper, and the consumption display corresponded with my math with each tank.

I first started noticing the decrease in MPG and acceleration power in March of this year at around 114,500. MPG went down gradually to 34 - 40 MPG over the next couple thousand miles and ICE always seemed to be running and took much longer than normal time to reach a full blue bar SOC as well as longer ICE shut down times at drive-throughs/stop lights.

Now, the sticker on the windshield showed it was already past due for an oil change by about 5000 miles when I bought it and I neglected to change the oil from 109,000 - 116, 200 but checked it once and found that it was too low, so I added a quart of synthetic 0-20 which I was told a few days ago by a guy at Toyota wasn't good for the mileage on the car, not to mention I added that 1 quart to the regular 5 w-30.

I read that overfilling may affect MPG?? Not sure I understand why that is, but I am pretty sure I might have put it over the fill line.

Anyway, after I put the oil in, it seemed to be getting better mileage again.

Later that month, I started getting bad mileage again.

A week or two passed and I found a screw in the rear passenger tire. I think a disgruntled neighbor may have had something to do with it, but nevermind that.

That day I went and fillid it up from 29 PSI to 42 PSI and drove it around a bit and it seemed to be ding better but still wasn't getting my normal 46-50 MPG.

Next day, I thought I may as well go ahead and get the tire plugged at the local Tire Kingdom tire shop and ended up paying $680 for 4 new tires and a front end alignment and was told I may need to get new shocks and struts to be able to properly align the rear-end.

Drove home and instantly dropped down to 39 MPG (average for that 6 mile trip.)

Next day went to get air for the tires as I assumed they didn't fill them with adequate pressure for good MPG and found they were all inflated to 32 PSI and filled them to 44/42 PSI.

Ride was pretty rough with new tires and still had poor mileage and ICE still running constantly.

Last week, looked up Mellors Automotive as being the only Preferred Independent Hybrid Car Repair and Service Shops in my state, explained to him everything I have posted here, and left it there for over a week.

Now here is the surprise: He said they had been all over the car and could find nothing wrong. He charged me less than $24 total for the oil change and for a diagnostic check.

I was upset that he didn't find anything because I had already convinced myself that the traction battery was on its way out or at least that SOMETHING was wrong.

Now, driving it home, I did not see any of my previous symptoms listed above and got home with 52 MPG average for that 25 mile trip going 60 mph on I-95.

So, these things came to mind of what could have been causing my low MPG:

1) He did something at the shop that he wasn't aware of or didn't tell me about that accidentally caused the issue to disappear.

2) It was the oil change itself?

3) I was carrying around a pretty thick layer of clean clothes in the hatchback of the car for many MONTHS and also in the back seat a few items, and by taking them out before I drove it to the shop, maybe it let the battery breathe better or absorb less heat since they were on top of the battery?

4) A combination of the above?

5) I am simply dreaming, and my car still runs like crap.


Hope this helps someone, because it sure has me confused....just hope it lasts and isn't a dream!

 

I had already dropped it off there but thanks a ton for trying to help with that info

And yeah, Josh was really cool about the whole thing and based on my experience I totally recommend Mellor's Automotive to anyone in Central Florida as a stealership alternative. He really was nice, seemed to know what he was doing AND didn't rip me off!

First time ever I had a good experience with an auto shop.

 

Well, the dream is over...I put my car into base drive coming off a steep bridge and afterwards the poor MPG started up again.