When should I start seeing back to normal/ better mpg after hybrid battery replacement

I swap batteries out in my car very frequently. I always disconnect the negative lead from the 12v battery before beginning any work. I've never had to wait for the car to 'get better' after an installation. I do understand that certain parameters of the engine will return to default settings and then 'relearn' as you drive, but I wouldn't expect (nor have I experienced) any significant amount of time like 3 tanks of gas. I would expect it to be quick, like <100 miles.

I usually take my car for a 47 mile round trip test drive after swapping a battery. Mine is also a 2007, those trips are normally 48-51 mpg with a fresh battery. 23.5 miles each way to a industrial parking lot and back to my driveway. Same route every time.

When 12v is lost, the fuel gauge defaults to one dot, but quickly (usually just a minute or two) recalibrates itself and will indicate true tank level, or at least what a normal prius thinks is true level.

 

what mpg's were you getting before the old battery started going south, and how many miles on your car?

 

TMR-JWAP will have been talking about HV battery replacement. He works with HV batteries all the time.

 

i mean before the mpg's started dropping off. with that many miles, i suppose there could be many culprits, and it would take some major testing of the battery to determine health.

 

Just baseline the car. Find a nice long straight flat stretch of highway get the car up to 60 miles an hour turn off the ac and the radio and the lights and keep windows up and engage cruise control. Zero out consumption meter on the mfd by hitting reset. Go 4 miles. Car should show at least 52 mpgs at the end of 4 or 5 miles On the consumption meter.

If not replace the inverter fluid and get an oil change use full synthetic. Tires at 38 lbs all around. Tires could be shot.

My car at 120k miles gets 55 mpgs in that test and I run non LRR tires at 36 lbs. I do run some very slick high quality oil at 10-30 buts it’s actually a 40 weight oil at operating temp. It has stopped my very minor oil loss.

 

10-30 means it’s a 10 weight oil until it reaches operating temp. So it’s actually thicker than a 0 weight until it’s warmed up if that’s what your after.

If your car is starting to really eat oil run a 40 weight oil like a 10-40.

 

You should do some tests on your engine. If it's burning oil (particularly a large amount of oil) then it could be getting tired and just not working very efficiently any more. Worn rings or valve guides usually. My old Honda did it too (like, clouds at high RPM), but seemed to make similar power to the other Civics I had with the same engine. It was a d16y7 bottom end with a d16y8 head.

Figure out how to check compression too. I'm not sure how on these cars as you can't just crank the engine to tell with the test tool. It would help you figure out if you have a cylinder down on compression indicating that a valve isn't seating or worse.

Running thicker oil like edthefox5 said may alleviate the problem, but it's obviously not the optimal solution. Your gas mileage will suffer to an extent from that too.

Burning oil is a big flag that says, "Things are worn." You may just see poor gas mileage until an engine rebuild.

 

The traction battery in my Gen 3 Prius was just replaced and my mileage went way down. I read your reply here, tried your suggestion, and now my mileage is above what it was before the battery had to be replaced. Thank you so much!

 

Excellent glad I could help!