Hey all, I recently changed the oil and the transaxle fluid on my 2010 Prius IV. The trans fluid was super dark, and at 156K I wonder if it had ever been done. Now i'm getting way worse gas mileage than before. I'm going to double check my work tomorrow to make sure there is enough/not too much fluid in the transaxle. I put in about 3.5 quarts until it overflowed, but could have waited a little longer for the excess to stop draining out. The oil level is fine. Any suggestions appreciated! Thanks!
If you pulled the 12v lead prior to the change then its normal to see a significant mpg difference whenever the 12v lead is reconnected.
PriusChat members used to mail in samples of their trans fluid to Blackstone labs and data said that there were enough particles in fluid to make it wise to change the original fluid once, so Toyota's claim of fluid being good for life of vehicle was found to be in question. But any trans fluid changes after that made no meaningful difference in fluid quality/purity. As in factory fill of fluid had machine break in particles, but follow up fluid changes didn't have a viable source of contamination because the planetary gear system of this particular transmission is so simple.
Good info, guys! I did not disconnect the 12V battery during this process. Should I do so to help the system "re-learn"? Or is it just a matter of having bad MPGs for a while, assuming the fluid level is correct?
I have no idea different driving style going faster who knows . No 12 v disconnect. Means everything should be holding the same values before you started the transmission job so who knows . But quite normal .
It could be unrelated. How recent was the transaxle fluid change, how many miles since, and how are you assessing mpg? Are just monitoring a trip meter, and when did you last reset it? Or is it several calculated tanks? anything else happening, say brake work, new wheels, different driving routine? regarding the fluid change, it sounds like you did it right, 3.5 qts refill is about the usual. There’s a link in my signature regarding transaxle fluid change; you could read through for a check. (On a phone turn it landscape to see signatures)
I decided to disconnect the safety plug and the 12 V negative for a couple of minutes and then reconnect. it seems to be back to normal, but I have only driven about 10 miles so we will see. I hadn't changed any driving habits or anything, but I did take it intentionally on the highway for a little while to see if that would help and also cycled in between the driving modes. I had previously done a bunch of work to it, like replacing the spark plugs, cleaning the EGR and the intake manifold putting on a new valve cover gasket, etc. but after all of that work, it was getting 40 miles to the gallon for about 1000 miles. Thanks for your input everyone!
That's generally a good first step if you're noticing lower than normal MPG... Also one tire low on pressure is one of the top causes too. And of course too much motor oil in the engine can have the same loss of MPG.
