Fixing gas milage deteriation in 2007 Prius

Check your tire pressures.
E-10 gasoline recently in your area?
Running your AC more do to warmer days?

 

Possibly a dirty throttle plate, which can be caused by chronically overfilling the oil.

Tire pressures up to the max shown on the tire sidewall (then subtract 2 PSI for the rear tires) allow better MPGs, but of course the ride gets harder.

 

There is no adjustment in software that is available.
As mentioned above:

1. Make sure you are getting 5W30 oil when it's changed.
2. Make sure the tire pressures are set accurately. I use 40 PSI front, 38 PSI rear.
3. If the fuel has changed to E10 it will lower the mileage slightly (5% or so). It will also burn cleaner, so in my book it's a "good thing" (tm).
4. Remove any external flags etc. They increase wind resistance.
5. You can check the throttle body for grunge by removing the air filter and looking in. I keep Pearl's oil at the "F" mark and haven't noticed any fuel mileage drop.
6. New tires? They can have a big impact on mileage.

 

I use Mobil 1 OW-20. Tire pressure 52/50 psi.

The biggest causes of decreasing mpg:

1) Proper tire pressure (too low bad)
2) Proper oil level (too much bad)
3) Outside temp. Cold = decreased mpg d/t increased warm-up time. Hot = decreased mpg primarily because of increase ac use and the temperature of the traction battery.
4) Length of trips. Short (3 miles or less) = lower than desired mileage.

On short trips in town I average around 40 mpg. On the highway I get 55-60 mpg at 57 mph with temperatures between 50-90F. At highway speed around 48-50 mpg.

Hope that helps.

 

This is interesting. How would I check this most easily?

 

Recent encounters with deep potholes, long stretches of really rough road
surfaces taken at high speed, or contact with curbing can knock the
alignment outside of spec resulting in increased tire wear and reduced MPGs.

Do you have any unusual tire tread wear patterns; inside/outside edges,
center of tread, cupping?

 

Visual inspection of the throttle body. Here is a search showing various PriusChat posts about this topic:

Google

Tom

 

Important distinction for the OP: If the dealer or owner is refilling the oil with Toyota's recommended quantity it will most likely be overfull on the dipstick, just like mine and many (most?) others were delivered. That is one reason why it is important to check the oil level immediately after a fill. On oil changes with any vehicle I tend to reserve the final 1/2 quart (4-banger) or a full quart (V8) until I've checked the oil level to avoid an overfill. Then I add what is need (if any) to bring it to a comfortable/safe operating level.

I presently run the Prius on 3 quarts of oil, which puts it right in the middle of the operating range on the dipstick for me, plus it saves about $5-6 per oil change with synthetic. Running at full on the dipstick is a hair beneath "overfull" so I can't recommend it. Moving to 3 quarts coincided with a long string of improved mileage for me (but other things were changing too so it doesn't qualify as proof--I didn't add back an extra half or full quart to see if mileage dropped.)

 

Ditto for me. I'm glad you mention it, actually, because I always thought it was weird that mine takes 3 quarts to get half way up the dipstick when 3.5 quarts is so often quoted as the "right" volume to use. For me that would be too much.

 

Sooo you have an 07.....Another overlooked gas sucker is a sulfated older battery (the small 12 volt one in right rear) ...when over 2-3 years old they loose their ability to become fully charged ,yet still draw amperage ...check your 12 volt battery voltage in the morning before you drive ...if it's below 12 volts that could be it (your car will still act normal but the ICE/traction battery is always trying to charge a battery that wont charge)...there are many desulfaters on the market.. ie. ebay... to desulfate a battery takes about 2 weeks with one of these things ...I have several and the work great! 80% of battery failure is caused by sulfation ,resulting in a weak battery......I have a Honda Insight as well..they tell you to check the 12volt battery if your mileage decreases.... for this reason.... A good battery should be 12.5-13.5 v.... Prius does not use the 12v batt to start the car otherwise you may notice the batt getting weak .....

 

PS ....check your battery with the car off ...

 

At 20K miles, my 07 is getting better mpg than ever. I consistently am 55-60 actual tank mileage at 60-64 mph on bay area freeways. I don't overinflate tires more than 2 lbs over 35/33, I use 3.75 qts oil at changes, usually duplicating factory fill level at about 1/8" over full mark. I have to disagree with others on that one, and find it does no harm. When the engine is running, oil left in the pan drops, and I definitely don't want any less. Switching to Mobil 1 5-30, the one that wears engines out 8X faster according to Castrol, made a noticeable difference, and I am going to 0-30 next change. I speculate one of the main ways the 2010 achieves higher mpg is the 0-20 oil.

Headwinds, and driving style make the biggest differences I find, as well as minimizing accessory use and weight. I find myself tending toward the styles of other cars around me, which is to say, bad driving style. When that is checked, mpg returns. With headwinds there isn't much can be done. A strong wind makes a huge difference.

 

That's about average for those speeds. Rule of thumb is ~60 mpg @ 60 mph in the GII, go up 1 mph, subtract 1 mpg, and the reverse is also true. It seems to hold up into the low 70's.

I've had my best mileage at 3 quarts in there, midpoint on the dipstick just as the manual and warranty suggest. I figure why waste the extra synthetic oil to overfill and risk warranty coverage? There is also some risk of oil aspiration into the intake with the factory overfill.

If you haven't tried a 3 quart oil change then you really don't know if the overfill you are doing is harming your gas mileage. You can always add a little extra oil, but it is more difficult to remove it cleanly and quickly.

The tires should last longer and wear better at 42/40, and they seem to corner better. But it does make the ride stiffer so it is a matter of tastes. Getting more even wear (longer tread life) and better gas mileage along with better cornering make this an easy trade off for me, but to each their own.

I liked your tongue-in-cheek comment about Castrol's claims. If Mobil1 wears engines out 8x faster, and my 150,000 mile engines on Mobil1 were not yet worn out when I parted with them...how long would they have lasted on Castrol? I doubt I'll ever own a single vehicle for 1.2 million miles.

Headwinds are painful but I'll take a headwind over a strong crosswind any day in the Prius. With a headwind you can draft in traffic at a safe distance and not pay a high penalty. But a crosswind is inescapable and results in a larger profile and a poorer effective drag coefficient.

 

Where is this battery found, can I have a toyota mechnic do this, I am partially disabled and doing it myself would be a no go....

 

Cycle your emergency brake on and off, clean your interior air filter, change your engine air filter, check your oil level, not to full, check your tire pressure, change your battery for an optima yellow top with kit.

A perusal through your owners Manuel is in order, it's in the rear of the car on the right side, not the end of the world to go to the dealer and have them test it, but if you haven't changed it, an optima yellow top with fit kit would be a good idea, the dealer would install it for you, but if you buy it from a supplier that installs they would also.

 

Im going to sounds really slow, but can you explain what a optima yellow top kit is? thanks! you have been very helpful!

 

Monica, there is a shop in Sanford, NC called Taylor Automotive. I don't know how close you are to them, but you can trust them to figure out your problems. Also, please review the questionnaire at http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html and report back here.

An Optima D51 Yellowtop is an aftermarket 12V battery that many of us have installed after having problems with the 12V battery from Toyota.

 

It's been found numerous times here on Priuschat that have a dealer test your OEM 12 volt is not helpful. Sometimes batteries that tested out "good" turned to need replacement. You can check the voltage of the 12 volt via the procedure at http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html. I would suggest checking the voltage after leaving it overnight.

Some dealers will not install parts brought in by the customer.

Toyota Prius 12 Volt Auxiliary Battery with install kit for 2004 - 10

 

If you're partially disabled someone else will probably have to install it. The easiest solution is just to have a Toyota dealer replace the battery with a new Toyota battery, which should cost around $200 total. The Optima battery mentioned above is good but with the installation kit the cost is about the same even if you install it yourself.