I replaced my 12V battery yesterday with the Optima yellow top. immediately after, my gas mileage dropped to about 16 mpg. Has anyone ever experienced this? Any suggestions? Thanks!
Check that the voltage on the new battery is healthy, and if so it's probably unrelated to the battery itself. There's almost an "epidemic" here of people reporting drastic MPG reductions after all manner of routine repairs and maintenance. The only common factor seems to be the disconnection of the 12V battery and the consequent (temporary) loss of ECU historical data. As long as the new battery checks out healthy, then just wait a few weeks and your MPG will return to normal.
Thanks. Voltage is perfect. I suspected it had something to do with math, and not actual mileage results.
Three things you do not give details on in your reply. How did you check the voltage? voltmeter or MFD display? What state was the car in when the voltage was checked? Off, acc mode, ign mode, or ready? What was the voltage you registered. Although you may have done the test correctly there is always the possibility you did not, and knowing these details also helps though's following you with less experience. John (Britprius)
agree with britprius, if the battery turns out to be solid, you need to test a full tank and refill measurement.
Sorry Britprius - here are the details... Battery was tested using the MFD. Prior to the change, the battery was reading under 10V with no load (pushed power button without foot on brake). It went down to 9 with a load (pushed power a second time), and then up to 14.3 while the car was running (Ready mode). After the change, the battery reads 12.3V with no load, 11.9 with a load, and 14.3 while the car is running.
Thanks for the update. For a new battery those voltages are rather low. A new AGM battery fully charged should be in the region of 13 volts off load, and about 12.5 or higher on load. A voltage of 14.3 with the car in ready mode suggests the charging system is working hard to charge the battery. This would indicate the new battery was low on charge when fitted giving you a low mpg figure. When charged it is normal for the Prius to have a ready voltage of 13.8 volts. John (Britprius)
many complaints here of optima's coming with less than a full charge. you need to put a trickle charger on it overnight and retest.
I just replaced the 12v battery two days ago. Same issue with the display reporting low MPG (sub 20's) and I also got the red triangle light. A couple of hours after a long drive that same day, the light disappeared and everything returned back to normal.
rivets, the low MPG indication has been seen often enough in this situation, but not the red triangle. Have you checked your oil?
