Reduced Gas Mileage

andyprius · Aug 16, 2010

Lindon said: ↑

I have no solutions, but I'm reporting more of the same. Since June 2010, my mpg has dropped from 50+/- to 40+/_ mpg. In June, the 2008 Prius had 30,000 mile maintenance and new tires. Toyota blames it on summer blend gas, but why the big drop now, prevous summers haven't been a problem? I try to avoid gas with ethanol and have been successful using the water test, so that hasn't changed. The tire pressures are ok, the 12V battery checks ok, my driving habits haven't changed. I can't imagine the new tires would cause a 10 mpg reduction.
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Try rebooting.

andyprius · Aug 16, 2010

Bobroberts said: ↑

I have a 2005 Prius -- initially, I was getting, roughly 46 miles per gallon (blended). Over the past 4 & 1/2 years my mileage has reduced to a little over 41 MPG today. Service department at the dealer states that they have never heard of this. I'm driving the same way -- between the same locations -- tires were replaced a year ago. Has anyone heard of this?
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Try rebooting

andyprius · Aug 16, 2010

Lindon said: ↑

I have no solutions, but I'm reporting more of the same. Since June 2010, my mpg has dropped from 50+/- to 40+/_ mpg. In June, the 2008 Prius had 30,000 mile maintenance and new tires. Toyota blames it on summer blend gas, but why the big drop now, prevous summers haven't been a problem? I try to avoid gas with ethanol and have been successful using the water test, so that hasn't changed. The tire pressures are ok, the 12V battery checks ok, my driving habits haven't changed. I can't imagine the new tires would cause a 10 mpg reduction.
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Try rebooting

andyprius · Aug 16, 2010

unixrocks said: ↑

Im still new here with my 2008 prius but after a lot of messing around heres what I found after buying a "certified prius" that was causing mileage issues - I was in the low 30s with city driving. I dont believe in trying one thing at a time - I would rather assess and if its questionable then fix it properly.

1. Front and back end alignment - mine only needed a front end

2. Airfilter - looks like the dealer "blew it out" and put it back in which meant dust accumulated faster than it should have - put in a new one which has stayed clean. Never blow these things out just replace em - not worth trying to milk them.

3. Cabin airfilter was CLOGGED - mind you this wont cause mileage issue more than likely but I cant believe they certified it without checking the cabin air filter - my nose is happier and I use the AC less with the increased airflow so just maybe it does have bearing?

4. Tires - the set on there was mis-matched?!!? I took it to goodyear and they fixed me up with some assurance fuel max tires which are still in break-in - to add insult to injury the weights for balancing the tires were on the OUTSIDE of the tire - on the Prius they are supposed to go on the INSIDE of the rim otherwise the covers dont fit correctly and god only knows how fast that throws the balance off. I chose not to go to sidewall ratings - let goodyear decide and they kept them at the Toyota reccomended pressures so I decided with a LRR tire Im not messing with it.

5. Oil - it was way overfull and thick (cheap oil?) - drained it and put in amsoil so its halfway up the dipstick with a WIX oil filter.

6. did some testing via the diagnostics screen while driving the car and found the main battery is dumping a huge charge to the 12V battery a lot while driving - this might be normal - in fact I suspect it is - so I am not replacing it yet since it shows no sign of going dim when I stress test it. However I believe the 12V stock battery is undersized for the vehicle - a battery with a higher rating would help since it siphons off the main pack and has to run all the accessories - I would think you would need to double the capacity to get decent performance....

Finally - after all that I was still seeing only a slight rise (went up to 35) in my mpg then it dawned on me to reset the computed mileage - once I did that and ran a tank througth it steadied out at 38MPG which given that Im a new driver - driving in the southern heat, 100% stop and go less than 6 mile commutes and still learning seems really good to me.

Some might see it as overkill but from my experience with other things - when in doubt fix it yourself or have it fixed properly by someone you trust. (I trust goodyear service centers - I DONT trust toyota or JiffyLube pepBoys etc...)

Oh yeah - on top of all that - the splashguard underneath was missing (the panel you take off when you change your oil) from what I understand this also helps regulate temperature of ICE and main pack - so I need to find a new one of those.

Same thing happened to me on my Celica - why is it SO hard for jiffylube and toyota to PROPERLY remove those fastners and put them back PROPERLY? I have no problems....why do they?

The oil and filter changes I did myself - the tires I left to the experts.

And the batterypack is now green a lot - before it bounced between purple and blue - it dont stay green for long which is healthy but it should go there now and then I think.

If your main pack is dippping down to purple a lot then I would look for whats draining it - using the AC will do it for sure - and even a lot of hills will do it depending on driving style since the electric motors give a boost to the ICE under high grades and relatively low speeds. A marginal 12V battery will likely do that as well very likely.

I dont like the Optima batteries - I wish there was a better solution - it still has a lousy AH rating - there are higher AH rated batteries but some are just too big and others I dont trust the way they mark them - I think they are fudging the numbers a bit on the cheaper ones....all part of the reason why Im doing the battery last if I feel the need.

So far....Im happy with what I got so Im staying there and see how it goes for a few tanks (which is a long long time LOL)

How on earth could all that be missed on a "certified" vehicle? Easy - cause even Dealers dont know what they are doing half the time. If you find a good one stick with them - if they suck then it is usually pretty obvious - just make sure you check EVERYBODYS work after its done and before you roll out the parking lot. =-)

Notes from a newbie - take them as such....

Oh yeah one more note - before I did all that the battery pack was always blue - first time it went green I nearly panicked I thought something was wrong since I had never seen it before lol
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So, did you replace your 12V Battery?

Reduced Gas Mileage

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