Decreasing Fuel Mileage

It is certainly possible that some fuel distributors are diluting high priced gasoline with increased quantities of cheaper ethanol and charging the same price. And, of course, more ethanol per gallon is going to drive down your mpg. I would try switching gas stations and continue to monitor.

Did your dealer actually scan for codes or just give you the ol-song-n-dance?

 

Is any significant portion of your driving in the city, and if so, are you running AC more? AC can really pull your fuel mileage down in city driving in the peak of summer heat.

What percentage of ethanol does your fuel have now? If it's gone from E0 to E10, that's not enough to drop fuel economy that much.

No need to use premium fuel. Stick with what Toyota recommends, which is regular. If premium helps any at all, it's not enough to justify the cost.

 

Just some thoughts

Air Filter? Fuel Filter? Spark plugs?

 

check oil level?

 

Go to your local auto parts store or Wal Mart and buy a bottle of Chevron Techron fuel injector cleaner <-- dont bother with the other brands. Dump it in the next time you buy gas. I guarantee that after you go through the tank with the cleaner your problems will be solved on the following tank. It's good stuff. It costs about $5 - $6 bucks.

Oh and get off the Premium gas.

 

+1.

 

Motors designed and tuned to run on regular generally receive no benefit from hi-test..unless the spark curve is altered via a tuner or after market module. Ever notice that they sell lower octane regular in the high mountains of Colorado...less air equals less octane required.

 

premium has less energy then regular... so don't use it on cars that don't require it.

 

I live in S. FL & have an '06 with 31K on it. At 30,000 miles I bought 4 new stock tires and expected a drop in MPG for a brief time. However, it's been over 1,100 miles since the tires were put on and my MPG is 3-4 MPG less than before I bought new tires. I also am thinking that ethanol is the guilty party. My '08 Prius is just barely making 47-48 MPG. I do realize that @ 2,500 miles the engine still hasn't fully broken in. I am very concerned over putting ethanol in my cars as I think it sucks.

I don't see how you're losing that many MPG though. Something is not right.

 

A few bad batches of gasoline with a substandard additive package may have put some gunk on the fuel injectors, intake valve backsides and caused combustion chamber deposits. These three items can cause both a fuel economy loss and a power loss as the engine runs richer than needed and adjusts the spark timing to compensate.

Surprisingly in this day and age of ripoff products and snake oil, there are simple, cheap and effective products to remove virtually all these deposits - those fuel cleaners that one adds to the gas tank.

Like so many things, some of them are better than others. What one wants are the gas cleaners that have PolyEther Amines (PEA). Sometimes there are other cleaners as well, but it must have a significant PEA fraction in it. Unfortunately the bottles on the shelf don't tell you what they have! One has to look at the Material Safety Data Sheets (MSDS) that every manufacturer must provide - many are conveniently on the web.

To cut to the recommendations:

Best category:

Red Line SI-1
Amsoil Pi

Both have plenty of PEA and a few other cleaners in them

Good category:

Gumout Regane Complete Also has plenty of PEA but no other cleaners (note - many Gumout products have no PEA in them, the Regane does for sure as does their large vehicle fuel system cleaner)

There are most likely others that have PEA in them, but the 3 above do for sure. Gumout Regane is available at many outlets and I picked up some Red Line SI-1 at Pep Boys. Amsoil Pi is available from an Amsoil dealer, or off the web.

Note on Techron: For a long time Techron advertised as having PEA in it. However, the MSDS for the Techron Concentrate Plus now shows no PEA in the formula. The Bulk gas additive also named Techron which is used in Texaco and Chevron gas *does* still list PEA in it's MSDS. So, the gas from Texaco and Chevron has a good additive package, but the bottle of Techron one can buy is not as good as those with PEA.

Rumple

 

Any thought that you might have a battery cell(s) going bad? Loss of storage capacity would result in continued downward MPG.

 

You're not alone. I recently bought an '05 and the mileage sucks compared to my '08 (yes, I have two Priuses). The '05 is getting the low 40s while my '08 is in the low 50s. Quite significant. The dealer couldn't seem to locate a problem with the '05. Funny thing is I'm driving both vehicles the same. The plug are new, oil level is fine, tire pressure's set at 40 for both vehicles. All things similar between the 2 cars, but a difference of 10mpg.