2008 Prius MPG dropping like a rock after new 12v battery and coolant pump change

hmm. check your tire pressure. Also check and make sure you seated the new air filter correctly. Have you cleaned your throttle body or intake manifold? How many miles on her? If you are 125K or more and original..it is time.

 

I think when you put in a new battery, the computers have to relearn everything.
Track a couple tanks and let us know the actual mpg’s

 

lol...the 12 volt battery has little to do with mpgs.

 

So which MPG meter are you specifically using?

If it is the Average dispalyed on the Consumption screen (which is a lifetime since last reset), then the is a high chance that this was reset when you changed the battery.

Depending on if you have ever pressed the "Reset" button on that screen then the average you saw before the battery change could be the average over many thousands of miles.

With the average now reset, the average will be since the reset.

The best way to know what is the true MPG is to calculate the true MPG by dividing the mile run on the cuurent tank by the numser of gallons you added the tank. Record the numbers in a biook (or better still create an account on fuelly.com) so you have a running record. When you fill up reset the Trip A and the average on the consumption screen. do the recording all over again at the next fill up. For this to work, you need to fill up completely, not partial fill ups.

 

You never stated the miles on the car or how long you have owned it?

You need a new hybrid battery based on what your saying. if you just bought it you def need a new hybrid battery.

Needs new hybrid battery is probably #1 reason people sell there G2.

 

Yup your in Stage 1 hybrid battery failure. A prolong charger can prop it up and get you another year and forced charging can help but its going to need to come out and be investigated before it leaves you stranded.

A failed hybrid battery on a G2 is the number #1 post on this site. very common its just the age of that car. 15 years is a awesome run on any battery.

Forced battery charging or power braking is very easy.

When your in gear and stopped put your left foot on the brake and then gently press the gas till you see the charging bars on the mfd start to route power to the battery from the engine. Not necessary to floor it just press the gas pedal down enough to start the engine and get the bars moving.

Practice with no one in front of you for a while to get confident at that. I did that for months at every traffic light before buying a Prolong..

It works it will add blue bars to the battery. Or at least get you out of purple bars.

Here's a link to the Search Forums list with the search word "Hybrid Battery Failing". Se how other people dealt with this:

Good Luck!

https://priuschat.com/search/429441022/?q=hybrid+battery+failing&t=post&o=relevance

 

OK

 

wow...

 

In town driving and short distance trips often result in lower MPGs, and disconnecting or replacing the 12v will cause the computers/ECUs to reset the learned fuel mapping/curves, which then reset to the factory default settings. Generally a good idea to clean the MAF sensor after any 12v work, unless already clean. Then use a toothbrush dipped in vodka or rubbing alcohol to clean the butterfly valve and throttle bore.