Mileage significantly decreased

Changing the air filter would be a good start, especially since your don't know when it was done and you aren't following the recommended service intervals from Toyota.

My advice: Don't have this done, do it yourself and save $$$$. An air filter costs ~ $10 and is the easiest thing on the car to change.

Open Hood
Find air box (It will be a rectangle shaped box on the passenger side of the car)
Undo 4 hooks
Lift off airbox cover
Take out old filter
Put in new filter
Put airbox cover back on
Latch 4 hooks
Close hood

It literally takes 2 minutes at the most.

 

Usually mileage drops are caused by the colder weather. Also, if your use has changed to include a lot of short trips in a cold car it will really drop the mileage. It goes back up when the weather gets warm again next spring.

 

Phyllis06,

Welcome to PriusChat.

Posters have reported that sometimes, especially in you drive in a dusty
area, the inside of the throttle body gets dirty enough to negatively affect
mileage.

It's not all that difficult to clean it, but there is the chance that you can
goober up one of the computer sensors in there -- air mass sensor?

I'm no expert here and I'm hoping that one of the engine smart folks will
come up and complete this idea; how to do it right, what to avoid, etc.

 

Phyllis,

Another tip to save you some money.. You don't need to change the oil every 3000 miles. Every 5000 miles is what the scheduled maintenance booklet specifies.

It makes sense-- Unlike a regular car, the Prius engine isn't running all the time the car's in operation, so you don't need such frequent oil changes.

 

Hi Phyllis,

Sounds like you will need a new engine air filter, but I doubt that would cause the specific mpg problem that you have noted. If nothing obvious is found, I suggest that you have wheel alignment checked and ensure the parking brake is not dragging the rear brakes. Good luck.

 

Changing engine oil every 3000 miles is basically very stupid. You waste money and time, you increase pollution and basically do not do anything positive for your car. We are in 2008 and not in 1965 anymore. Both engines and oil formulations have evolved significantly over last 40 years. You will do much more by keeping your tires properly inflated than with premature oil changes.

 

How often do you check the tire pressures? Under-inflated tires are probably the single biggest waster of fuel. They should be checked at least monthly.

 

First you have to keep everything in perspective. A Prius can get around 50mpg. What you're experiencing is about a 10% drop. In a "normal" vehicle you may barely notice the 10%... it's magnified on the Prius.

With that being said, it's easy to "lose" 10% of your fuel economy.

1) Low air pressure. Tire pressure "leaks out" continually. It's slow, but it happens. This is why you have to check your pressure somewhat regularly. This problem is made worse by the lower temps. The lower temps also lower pressure. Combine the two, and you could be down 10lbs very quickly. This is the number one reason for bad economy.

2) Cold temps in general. All modern car's computers priority is to bring the engine up to temperature. This is for emissions reasons primarily. The catalytic converter has to stay hot in order to work. In all cars (the Prius included), the engine will run richer to facilitate this. The Prius has one more thing against it. In order to generate this heat, the engine will be running in situations where it might not run in warmer weather...reducing fuel economy.

3) Over-filled oil. This seems to be observed more in a Prius than other vehicles. Again, it's probably because it's relative to the overall MPG a Prius sees. A few percent difference is not only measureable on the Prius, it's right in your face.

If I were to speculate about your latest oil change for a moment... I've found in the past (do all my own service now) that the oil change places typically check the dipstick and call it "good enough" when doing oil changes. This good enough could be a bit too high. These service centers also check the tires. I can picture them adjusting them down to 30psi. Many places don't check/know what pressure the tires should be at so they automatically adjust them to either 30 or 35psi (although some fill up to the max rating). If your tires were warm heading in and they adjusted them, this too could bring them down to below optimal for the Prius.

There's a very good chance your tire pressure is low, your oil level is too high... and the ambient temperature outside is causing this 10% drop that you're experiencing.

 

All the suggestions listed above are good ones. With the age and mileage on you car, you might was to get the fuel injection system cleaned. Dirty or clogged injectors can diminish gas mileage. It takes about an hour at your Toyota dealer.

 

Nobody has mentioned that perhaps they put a thicker viscosity of oil in last time you had your oil changed, or even overfilled.

 

I would not be surprised to hear of a large % drop.

The cold weather, 10%-20%
10% winter blend fuel
10% low tire pressure
Short trips 10%-20%

As others mentioned, ck tire pressure, and filters.

 

Some have noted issues with the mass air flow sensor, which is a "hot wire" meter. You require a special cleaner to clean this, otherwise you risk ruining it

My FJ Cruiser needed the mass air cleaned. I noticed the fuel economy slowly declining over summer. Picked up a can of CRC Sensor Kleen for under $6, the FJ mass air meter was dirty.

CRC Canada > Product Catalogue > Automotive > Cleaners/Degreasers > SensorKleen?

There appeared to be a light ash residue on the two hot wires. The popular theory is that routine operation of the PCV introduces oil vapor into the intake manifold, which when it lands on the mass air wires turns to ash. I've posted photos of the before/after

There was a big difference in my FJ. I cleaned my Prius and there wasn't any difference. The dealer cleaned the MAF last year, so maybe it wasn't that clogged

 

This sounds like a problem. I know when I shop for an Earth-friendly car, I look for mileage, warranty (if it's used), and engineering.


I think some of these other posts are accurate. I would consider writing in to the manufacturer and ask them how common this problem is and then post here what their response was.


God bless!

 

I like your Father, he taught you well.

 

I have a 07 Prius and it has lost mpg too- this is WInter but it did the same in Fla when I was there. Have recently had new tires on at dealer and oil change and then is when the lower avg milage is showing up- goes like 43 avg instead os 50 and 60's. I have been back to ask and they checked tirepressure and said it was not that and it was probably WInter. I am not sure who to believe- does anyone know also about the 30,00 mi very expensive general checkup Toyota recommends? General things like tires, oil, brakes , fluids and so on for over $200. Is this necessary? I really like my Prius but am not sure if anything is wrong or not with this big drop in milage. Thanks, Joan

 

What do you guys recommend for tire pressure?