Gen 2 with 220K miles, sudden 10 mpg loss, 12V battery?

Simplest check would be to invest in a half-dent digital multimeter. Check voltage with the car off, at the under-the-hood jump point (assume second gen has this?). A battery in decent shape will read over 12.5 volt. A faltering battery: 12.2~12.4. Any lower, it's near dead, should be replaced, or you can attempt recharge. For more in-depth assessment, something like Solar BA5 will do an electronic load test, tell you the current Cold Cranking Amps of the battery, and give a verdict, either good, good but recharge, or fail.

Any decent retailer selling automotive batteries you should have a pro-level equivalent to the BA5, be able to run the test for you.

Doors open, lights left on, 4+ years old, needing a jump start? All this says it's time.

You can look into chargers too: a smart charger in 3~4 amp range is what you need.

 

Yeah, could be other issues, but the 12 volt is the "low hanging fruit". If you don't want to get into tool investment, yeah: replacement is a good first step, considering it's age and what's been happening.

But really, a $20 multimeter is invaluable first step, towards getting some insight into what you're 12 volts doing. Or just mundane stuff: like if you've got some lose AA batteries, and you're wondering if they're dead or good. Or small appliance repair, household wiring and so on.

 

I would rather KNOW if the 12v was suspect and if not, save the $200 for a new WB Oxygen sensor that is also a top contender for this issue.

 

Yup, the 12v is DOA.

Bank 1, O2 1 is the WB on a Prius. Depending on what brand of sensor it is, it should read in the 2.5V+ range (stoich or trending lean), if <2v, it's running rich.

 

what were your mpg's on your last full fill up, manually calculated?

 

have you always gone by the dash display for mpg's?

 

i'm sure there is some data to be mined there, but there are so many things changing so rapidly, it's difficult to get a handle on. most of us track our mpg' on fuelly or other, and it gives a better picture of trends.

 

have you had any dash lights?

 

i'm not that knowledgeable. i suppose there are many items not performing up to spec on a high mileage car, that cumulatively, could add up to 10 mpg's.

 

My 06 has 282k and my 07 has 162k and both use oil about a quart or two between oil changes but really depends on driving. Extended highway at 75+ I use more oil. A lot of newer cars use oil by design due to improper break ins. I just check it every couple fill ups as cheap insurance.

 

No OEM designs engines to use excessive oil amounts, for any reason and few engines require a break-in period, while many have not for a decade or more (in some cases, 3 decades). Typical high performance engine designs use dramatically more oil than a quart every 5k, which is what most OEMs aim for.

You are spot-on, higher engine speeds will transmit into higher oil consumption rates. This is especially common with these cars.

 

I know this is a dead thread but just wanted to post a phenomenon I experience that could explain your MPG loss.

It has to do with the 12v disconnecting/dying and resetting the Hybrid ECU's. The relearn parameters to return your Prius to max efficiency are not so straight forward. Explained in detail below.

Hybrid System Less Efficient After 12V Disconnect



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