I bought my 2011 Prius in February (new) and have been LOVING the 51-53 mpg I have been getting consistently since. Two weeks ago, it went in for the 10k mile tune up and tire rotation/balance and now I can't get over 45.6 mpg. Any idea why? We also have a 2012 Prius V and it is now getting the better gas mileage!!
Have a quick search or look back at previous posts regarding 'wrong oil'. The Prius from the gen3/2010 onwards requires a very expensive synthetic oil rated at 0w20 to enable the car to get the best fuel economy. It is possible to use 5w30 oil (as used in the older gen2 Prius) but your mpg's will suffer quite significantly. If the dealers have used 5w30 to cut costs, then that might be the reason. The 0w20 is very expensive. Here in the UK it's about £50/£60 for 5 litres. Check your invoice or give the dealers a ring to check. Also check the tyre pressures as if they are lower than they should be then that could be the reason too.
Strictly monitor the correct amount of oil put in car. In perhaps as much as 90%+ the dealers over fill which causes a reduction in MPG. I give them 4 qts for our Prius and top off myself as many others do too.
