2008 Prius Loss of MPG

Hi John, new tires are one of the most common causes of loss of MPG. Can you post the exact brand/model and size of your new tires.

It may have been that you didn't notice the loss of MPG from you new tires until the MPG data was reset. (or perhaps it was a slow moving average). In any case lets try to rule out the tires first.

 

Agreed with uart's questions and hypotheses. From http://priuschat.com/forums/gen-ii-...answer-these-questions-esp-if-youre-new.html:

If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute?
Is your oil overfilled? (i.e. above the full mark on the dipstick)
Have you had your alignment checked? Any pulling or abnormal tire wear?

 

Betcha they let some air out of the tires. How often do you personally check their pressures?

Certainly something changed: different driver, different routes, different distances per trip, new tires, you started using the A/C or the heat a lot more, ...

 

I have a 2008 with 55K miles, I did change my tires in Jan, however I noticed a decreased MPG months before that-I have been using low grade fuel (my oil changes are regular, air filter always changed) the issue is, and what no one is mentioning is the fuel rail-the fuel injectors and the mass air flow sensor must be flushed! Fuel additives will do nothing, you must clean the fuel system-it can be costly, 200.00 plus they will still want to scan for codes, another 100.00 but well worth it! I am back in my 49.5 zone after falling to 47 MPG!

 

I'm not convinced your above work was the cause of the improvement.

Things I can think of: warmer weather, your area possibly switching away from winter blend gas now/recently, and your new tires being more broken in. See Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires. Count on a mileage drop again next winter.

 

I agree with cwerdna and his diagnosis but living in the warmth of Hawaii have you been monitoring your tire pressure? It is possible that your levels are slightly lower than you are even running them at and has weather changed last few months? Rain wind all can adversely effect fuel economy and be compounded by low tire pressure.

 

I want to start a count of how many people come in and make a single post about something wrong with their Prius then never post again. Ever.

 

To make sure I don't make that list I am making a second post in this thread!

 

It's only been 10 days. It takes a long time to get here typing all the way from Hawaii.

 

Sweet! lol

I blame the return of La Niña conditions.

 

I'm telling you it's not the tires! This is my second set of factory GY and I drive 500 miles a week/24K/YR and I get gas here in the southwestern region of Texas which has been proven to be the worst low grade/added alcohol, (Valero) which is used in Texas and I am in Houston at sea level-weather humid and warm year round (winter was mild-temps avg 38-48 for approx. 3 months) anyways, believe what you want, I happen to work in the auto industry and call on mechanical & collision shops for a living-my car is my tool for the trade and I drive in it a constant 8 hours daily-I have air available at all times and carry my own tire guage (plus the lil light comes on too to let me know I'm low) so it's OK if your not convinced but my real concern is what is going to be the life cycle of my battery? But I will save this question for a new thread....

 

Again, I'm still not convinced. 49.5 to 47 mpg drop isn't large and could well be accounted for by both the winter gas blend and colder weather.

See:
Why does mileage drop in winter? — Autoblog Green
Cold Weather Vehicle Fuel Mileage – Why Winter Fuel Economy Drops – Fuel Mileage Drop in Vehicles
Car Talk
Why does gas mileage drop in winter?

If you had any rain, that also will hurt fuel economy.

 

You may have answered your own question. If fuel is of such an inferior blend maybe it has an excessive amount of ethanol . Which will cause a decrease in fuel economy you should maybe try to stick to shell for a few filler ups and see if it improves.

 

Yes, the MAF sensor may need to be cleaned at long intervals, but an injector flush is just a wallet flush. Use E10 gas and the injectors will always be clean.

 

I have been experiencing loss of mileage on my 2009 Prius ( 2years 11, 700 miles) for about a year now. I moved from Maryland to Miami in June 2009 soon after buying my Prius. In MD I used to get around 47-50 MPG that dropped to 43-45 MPG in Miami over the initial few months. I attributed that to the summer heat and the load on the A/C( my pregnant wife also did not help- she liked to keep the A/C temp really low!!). Over the next year the MPG stayed around the 42-45 range. Bu since last April I have noticed the MPG declining steadily-its not a rapid decline but a tenth or two-tenths of a mile over each gas refill and is now hovering around the 36 MPG range. Now I must say that I have a very short commute ( 3 miles each way) to work everyday and that pretty much is all that my Prius does during the week ( 11, 700 miles in 2 years). The reason I bring this up is that whenever I have taken long drives ( 2 over the last year- each over 300 miles) the MPG goes back to the 45 MPG!! I am wondering if the short nature of my commute is a factor but then how can it explain the loss of mileage over the last year when it was same commute the year before.

So I am perplexed. I mentioned this to the service guys when I took my Prius for its scheduled maintanence but they seemed to take no notice.

BTW I have not changed tyres and keep the tire pressure at the recommended levels. IN fact once I did try keep them a little over-inflated. That didn't help either.

Does anyone else have the same problem? Or any suggestions?

 

By recommended do you mean 35 PSI or so? Going higher, up to the max shown on the side of the tire, will help noticeably. The short drives are certainly a, or the, major contributor. As to why this showed up only slowly: does the 2009 show lifetime MPGs unless the display is reset manually?

 

It's the short commute that's killing your mileage. You've proved that on your longer drives. Whenever they're long enough to completely warm everything up and you see the old mileage come back on the mfd. Of course you are still burning less gas on your short commute, so there's that. That short a commute could also maybe be handled on a bicycle some days for more savings!

And welcome to priuschat!

 

My milage on the 2008 suddenly nosedived as well. I thought for sure there was nothng I was doing so I continued driving for a while until I finally got sick and tired of 28 mpg and began to scrupulusly monitor my driving. I have got it up to 37mpg in town and 51 mpg on the road, but that is my tops. I talked to a friend's husband who is a former Toyota mechanic and he said driving style and tire pressure are important, but the truth is that even though Toyota markets the car as a high mpg vehicle the truth is that the design of the car is to provide a Green car rather than a high milage car. My mpgs were about where they should be once the car is broken in if I drove it like a regular car. Where you drive is very important as well. The idea is to get up to the speed limit as quickly as possible anwd then keep it there with surge and soar. That is hard to do living in Seattle. People ho live in flat terrain areas have a lot better milage. That aside, I have discovered using Cruise as much as possible really helps. I even put it on cruise in the city when on an arterial and it helps.

 

the truth is, you are clueless and need to read up on mpg threads and talk to your p.norwest brethren for hel and advice. the truth is, the prius is a high mileage car for those who care to drive correctly and learn about their vehicles condition and performance.