Low MPG and Dealer "upsells"

Let's resolve the poor mpg first, the maintenance is just something they get off the owners manual schedule.

1. Change the engine air filter
2. Check your tire condition and tire pressure. Inflating to 40lbs will help mpg
3. Check for proper balance and alignment of your car's tires
4. Make sure there are no braking issues that may reduce mpg
5. If you are blasting your AC, it will decrease your MPG
6. Cleaning the throttle body and MAF sensor may help the car run a little more efficient.
7. Check the condition of the 12v battery, if it's over 5 years old and weak, it may be affecting MPG

Maintenance items needed around 120k miles

1. change spark plugs
2. change both coolants
3. change transaxle "lifetime" fluid

 

you may want to invest in a code reader (scangauge 2) just cause there are no lights on dosnt mean you are not getting any codes



'5. If you are blasting your AC, it will decrease your MPG" very much so. I set mine about 5 derg below outside temp (enough to keep the humidity down)

 

Does the car burn a lot of oil? As the engines get older, they are less efficient....especially if they burn a lot of oil

 

windows down? kills the areo

 

follow the maintenance schedule that came with your car.

 

Here is an important questionnaire to give us more hints, while pointing you to common problem areas (though it missed brake drag from frozen calipers): Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat

From your info so far, I'd note that you could increase tire pressure a bit for a small improvement, though that is your choice. Higher pressure is not without controversy, and numerous folks dislike the harsher ride. New tires won't help MPG at all, in fact they will temporary decrease MPG. But good tires are a safety issue, so don't hold back for MPG reasons.

AC does matter, but other variable factors may have masked it in your test. AC is also a human necessity in many climates. Just don't turn it on stronger than necessary.

Coolants are not as easy to change yourself as you may expect, as you may not have the tools to get all the trapped air out.

The k&n filter is controversial, and generally doesn't have a good reputation here. It won't hurt MPG a bit, but engine longevity is an issue. It is meant for uses where high power is more important than engine life. Anyone who needs that kind of power, isn't driving a Prius.

How much aerodynamic cross section do the light bar and roof sign add? These are real factors, I'm surprised you initially lost only 2 mpg. My bicycle hitch rack, carrying two bikes, causes much more loss than that.

 

Low Rolling Resistance tires can make a significant difference.

Does the traction battery's state of charge rapidly fluctuate?

Does the car sit enough powered up that the engine fires up to charge the battery?

 

It is hard to say what is wrong with your Prius. Changing Spark Plugs is fairly easy and not to expensive. It could be many other problems. Could even be your hybrid battery going bad.

The coolant flush and fill is due to be done and if the transmission fluid has never been changed that should be done too. But I don't think those would kill your mpg that much. Figure out the mpg problem and then look at other maintenance items.

Glenn