Warm weather super green battery action!

I have tried searching, but I haven't quite found what I'm looking for. Here goes - I'm mostly a highway commuter, 43 miles each way, with 41 of them on the highway. I'm pokey. Yup, cruise control, 50mph (shift work, and 95% of the time against the heavier flow of traffic).

What I've noticed owning a Prius so far: temps below 50 degrees (and winter gas probably) seemed to give me tank mpg of 48-52. Warmer spring weather bumps this up to the 52-55mpg range. The start of our Southern warm weather (and a set of Bridgestone Ecopia's ) has my last few tanks at 57-64mpg. All of this makes sense. Now, the question.

The past few days when leaving work (temps between 85-91 - car is parked under the sun on a hilltop, so it's quite warm), I leave work and get on the highway. The display shows that the ICE is powering the car and charging the battery. OK, seems normal. Except it keeps charging the battery until it's green. And then keeps charging the battery until I reach an incline, where the battery sends power to the drive and keeps me powering through the incline (and for some time after I return to level travel) all the while keeping my mpg in the low 60's. This continued the first time for about 20 miles until I drove through some rain, at which point the magic green battery charge reverted to the normal blue and the mix of charge/use that I am used to seeing. The second time this happened, it continued for almost 35 miles of my drive, until I hit some stop and go traffic and it again reverted back to normal "blue" operation.

My bar display has shown that my commutes home the past few days have been 75mpg+, which of course makes me suspicious. The change in the operation of the hybrid system makes me suspicious. I'm not exactly complaining, of course, but since I just had a major accident in it... well, I'm wondering - what's going on? Is it simply warm weather effects? Any help ( or links to help) are of course greatly appreciated.

 

My accident was a rear-end collision at highway speeds. I had the hatchback, rear bumper, and rear left side panel replaced. Lots and lots of bodywork to put the car back together, but no frame damage. The body shop (Toyota sent the car to the local Chrysler-Dodge-Mitsu bodyshop) did their thing, and then Toyota had the car for a day to check alignment, hybrid drive et al. Everyone gave the car a thumbs up, and I have to say the first few hundred miles post accident have been just like I remember - great driving.

 

And that's the thing - my commute here in SC is very flat with very few gentle, undulating hills. That, and the fact that it's only been on the two hottest days of the year where I have seen this happen. Perhaps I'm just being hyper-sensitive with the car in the first few weeks after getting it put back together. Please let me know if your search finds any older posts - I've tried a few different times without much success.

 

JimN - I haven't yet taken the scangauge plunge (that's on the birthday list), so I cannot say. The Prius certainly has been pre-warmed on the two days this has happened, getting a good roasting in the parking lot. Being here in SC, I'm sure I'll be able to confirm with time that it's a temperature related issue, as our summers are rather... warm.

 

OK, yesterday's commute home from work started at 80F on the temperature reading... and voila! Super Green state of charge for the first 12 miles of the journey, then a return to normal 6-blue action for the rest. Initial internal car temp (as I do drive without the AC and the windows take some time to cool down - not usually until the highway breeze kicks in)?? I'm stumped, frankly. I would have asked the service guys at my local Toyota on Saturday, but I had an AWFUL initial experience just trying to set up an appointment and get prices from them, so that didn't happen.

Anyone? Anyone?