So I had a Dealership say that I should keep the ECO mode on, use non ethanol fuel and the mileage will return. I'm going to call Shenanigans. (I'd use a more colorful word but this is a polite forum HAH!!). My car has 244,000 original miles on it. Yes I lived in it. sort of. well taken care of. 2010 Prius was getting 50-55 MPG until 2 or 2 and a half years ago. Work done in last year to correct. (this is aside from regular servicing and tire rotation etc....) mileage first dropped to 45 MPG then 40 MPG the last year and now is getting 35-40 mpg... Work Done in last 12 months 1. Replaced EGR Valve and breather (totally caked up with black gunk) 2. Recently cleaned the Mass Air Intake sensor 3. Transmission fluid flush and replace. 4. Inverter Fluid flush. 5. 12 V battery replace in last 12 months. 6. Spark Plugs replaced Other symptoms (related? Unrelated?) 1. MPG drastically reduces while running the are (10-12 MPG loss) 2. Engine seems to run hot easily while air is on (heat knocking you hear on most small engines while in traffic) 3. AC Blower Moter has burned out and been replaced 3 times in 3 years. Havent tried having the intake manifold(s) cleaned out. Could be a low exit of the exhaust causing bad fuel efficiency? open for ideas.
tyres and pressure? check the 12v health, just in case? throttle body? pcv? i have to say, the hvac fan is odd, i wonder if there's an extra load? air and cabin filters? injectors?
So I observed the fuel mileage drop and was concerned about the HV battery, I recently had the engine swapped and my mileage jumped from an average of 39 back to 46.5. My EGR valve was swapped under the service bulletin but the cooler was not covered. During the engine swap my mechanic showed me the cooler from my old engine it was a solid carbon wall. (no wonder the check engine light remained on.) They cleaned and installed the cooler that came with the replacement engine. You may want to clean the EGR cooler as well as the intake manifold and see if your mileage goes back to normal. Or it could be the gas engine is near the end of life and is just not as efficient as it once was.
It sounds to me like there something dramatically wrong with the AC. Maybe the compressor is starting to go and pulling a high load? Don't forget that it runs when you use the defrost as well, I believe to pull humidity from the air.
