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Has anyone heard of something like this happening: I was getting ~40-43mpg on my 2001 Prius (roof rack and hilly Seattle) pretty much since the day we bought it (April '01). I got the postcard from Toyota saying that all 01 - 03 Priuses need to have the HV battery updated so I took my car to the local dealer and had them do that as well as the 3year/45k tuneup. When they took the car in, they said it needed 4 new tires as well. When I drove out of the dealership, I was getting 36-38mpg. Several months and many tanks of gas from different stations later and I was still stuck at 36-38mpg. I mentioned this when I took it in for the 50k checkup and they found nothing wrong. When I drove off the lot after that checkup, I was getting 35mpg! (Granted, it's only been about 50 miles since that checkup so things may change...)

I've heard that new tires can cause the mileage to drop, but that usually goes away after the tires wear in a bit. Has anyone else heard of a 10+% drop in mileage following the HV battery updated? Any ideas out there?

TIA,

Mike
 

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Did you check your tire pressure? Bet they put it low, and unless you've changed it, that could be the problem.
 

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I should've mentioned that I did check the tire pressure -- they usually get it too low at the Seattle Toyota dealership -- and I don't believe that's the problem.

mrv, when you say "temporarily", how long are you talking about? The update was done in Nov '04...

Thanks.
 

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Since all the electrics are disconnected for the ~4hr procedure, any learned items in the ECUs are lost (including the battery calibration). Depending on your driving, I would say up to a month for everything to get back in place. I say temporarily, as people have commented about the lowered MPG, but they never repost about it getting back to normal or continuing to stay low...

(It was a very cold night when I picked up my Prius after the battery sealing, so heater was on full the entire way home. MPG easily went down...)

Lifetime MPG has been very gradually going down on my 2001 for a while now (I think I'm long overdue for an alignment), so I don't know when things went back up. There's over 30,000 miles on my Consumption Screen odometer right now, and I did get it to go back up .1MPG this summer after dropping .2 last winter (which included the SSC 40G update)...
 

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My MPGs dropped with the TripleTreds for about 12,000 miles, and even now I can maintain 47MPG around my side of town but just driving to and from work can't get that high. Roadtrips are the only MPG booster. The OEM tires were good for 47MPG (at least) wherever I drove.

So, when these tires expire I'll have to think hard about what to get. Even another good deal on TripleTreds might be hard to justify if gas is high...
 

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I too had the dealer do the service in Nov '04. Through December and January I was barely breaking 40 MPG. I don't know if it was the weather or the service but I chalked it up to a cold winter not knowing the service itself might have caused it. In the spring I was up in the mid 40's and now thorugh the summer and into October I'm averaging 50 MPG again.

I just thought the drop in mileage was the weather. I never thought to think the service would have been the culprit, or part of it anyway.

Gives me something to ponder.


Hmmm.... <--- *me pondering*
 

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Seven7 said:
I too had the dealer do the service in Nov '04. Through December and January I was barely breaking 40 MPG. I don't know if it was the weather or the service but I chalked it up to a cold winter not knowing the service itself might have caused it. In the spring I was up in the mid 40's and now thorugh the summer and into October I'm averaging 50 MPG again.

I just thought the drop in mileage was the weather. I never thought to think the service would have been the culprit, or part of it anyway.

Gives me something to ponder.


Hmmm.... <--- *me pondering*
It was the weather. And here it comes again. Get ready to watch the numbers go South if you don't. :wink:
 

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Just my 2 cents.....

You know there is one thing that kills gas milage big time that you never hear mentioned.It's the thermostat.I would imagine just even a sticking one of these might make a HUGE difference it could be the reason why there is such a difference in gas milage from one Prius to another. Milage you get with this car is related to the warmup time and a thermostat that doesnt close well will let cold water in and the engine would have to keep running longer to finally get up to temperature.I have had 2 cars with sticking Thermostats and there was a huge difference in both cars.One of the cars barely had 30K miles when the dealership found the cause of the higher than usual gas consumption.

Ed
 

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Ed, I would think the ECM would monitor the thermostat very carefully because of this and give you a "service soon" warning if one left the parameter. With my "scan guage" installed and monitoring RPM, speed, coolant temp, and voltage at all times I can tell you that my car has a 180 degree thermostat and after five minutes I have never seen anything but 178 to 182 degrees indicated.
 

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I don't know about the Prius, but my SO's Infinity picked up the stuck (open) thermostat by virtue of the longer-than-normal warmup time, storing a trouble code.
 

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I've had 2 vehicles that developed thermostats stuck open. This is where a dash temp guage comes in handy. The vehicles had over 100K on them though. One was a 88 Honda Accord, the other a 92 Nissan Sentra.
 
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