Drop in fuel economy after a my Prius took a bump :(

the battery could also be shorting internally, causing a drag on the inverter. j denenberg had a pretty good write up in the thread, 'why does a bad 12v reduce mpg's.'

 

I'm not an engineer, but I'd be surprised if a shorting battery could be impacting mileage to that degree without catching fire.

 

10%? maybe.

 

As far as reading the 12 volt battery voltage, accurately, maybe just cave in and get a digital multimeter, read the voltage when the car's off? I wouldn't rely on the car's display, for anything.

 

Brand New Tires...

Which I'm willing to place my bet on are the reason for the MPG drop.

I'm not afraid to speculate. When someone asks for "advice" over the internet, that's all anyone really can do.

I assume anyone reading my posts, realizes that any advice could be right, wrong or some degree in between.

 

Well do the math. 10% of 10 kWh (for argument's sake) is one full kilowatt-hour. That's a lot of energy.

 

that means nothing to me in regard to how many mpg's a bad battery can cause to drop.

 

Energy can neither be created nor destroyed (also known as the First Law of Thermodynamics), Therefore any energy not propelling your car is likely being expressed as heat somewhere. This is why an IR thermometer is a good diagnostic tool. The difference between a high-mileage tire and a lower-mileage tire will manifest itself in the temperature of the tire.

 

So do I use a rectal thermometer or under the tongue?

I'm guessing (PURELY A GUESS) that the OP's older tires were worn quite a bit, thus the rolling resistance was really low. Now a new set, designed with a middle way level of rolling resistance, but with brand new tread and much more grip has caused the OP's baseline MPG's to drop.

Yep...I could be wrong. But that's the horse I'm betting on.

 

There's also a margin of error proportional to the inaccuracy of the measurement. If you "eyeball it" with rough mental calculation, the margin is wide. If you do precise measurements, the margin is narrow.

 

Just the flat of the hand on the rubber is usually enough to tell.

 

i think that's why they allow some margin of error.

 

I'm guessing the OP is in the UK or Europe as the A-F tyre rating is a mandatory rating here for fuel economy (amongst other things). A is super eco, C is middle of the road (and can vary if winter tyres) and F is poor economy.

I have a set of A/A rated Bridgestones and they're really amazing for fuel economy. I also previously had a set of C rated tyres which were ok but the A's made a big difference.

I think it might now be time for the profile to have a mandatory location setting as members can be from all over the World and knowing where they are helps with diagnostics, or saves time at least.

To the OP, yes C rated tyres will make a good 5 mpg difference, as will using any oil other than 0w20; many places (esp none Toyota dealers) still think 5w30 oil is fine in a gen3. It won't damage your engine but it will ruin your fuel economy. There are three items that do affect Prius fuel economy in a gen 3; none 0w20 oil, C or lower rated tyres and a failed/failing 12v battery. Correct all these and the car should be fine in 9/10 cases.

 

First thing before worrying about any fault codes is to ensure your 12v battery is healthy. If it isn't it likes to cause all sorts of weird and wonderful messages to appear.

If it is healthy then I trust you had the inverter recall carried out early last year? Not sure? Check this; Recall Checker | Toyota UK

 

The recall was to reprogram the inverter software as early gen3's had a tendancy to fry the inverter. I know that because mine did exactly that at about 71k miles. It was outside the 60k mile warranty but Toyota replaced it for free. I think they knew there was something going amiss with inverters as others had reported similar failures, though usually at higher miles (the car was only a couple years old at the time). Since the new inverter and software recall the car is just as economical as before, maybe ever so slightly more so once it had settled down, BUT it doesn't have that amazing whoosh of acceleration in Power mode that it once had

I have the base t3 model and have the 15 inch tyres. I got that version especially because of the wheel size as taxi use hammers low profile wheels and the tyres were double the cost. With the 15 inchers I got branded LRR tyres for £70 inc fitting etc, with Chinese cheepo's at £45. The tyres I have are the Bridgestone EP001S A/A rated and they were about £75 each. They really made a big difference to economy and the car just glides along for ages with no acceleration, barely slowling down. The wet grip is still bl**dy good and I like to 'drive' my Prius from time to time. It has been round corners and roundabouts in ways it really shouldn't

Bridgestone -

They're quite popular and almost impossible to source. They used to be on blackcircles but gone from there now too. Regarding the noise. They're ok, but I think those concrete motorway sections are just dreadful on pretty much all cars. The Prius is a bit crap for sound proofing though.

 

seems you measured it while it was in Ready then you measuring the DC/DC charging circuit voltage !!! NO WAY 14 V even on open circuit possible ...

you should measure the open circuit voltage (under the hood is the easiest at the jump point) after a few hours the car stopped and it was on for a while 1.5 hours drive or so...

you need to do this without opening the driver side door !!! otherwise the break cylinder will charge up and put load on the battery before you can measure it....

not sure if you can measure it with the car computer in ACC mode (when the start button is amber NOT green)