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post #1 of 5 (permalink) Old 02-26-2013, 01:21 AM Thread Starter
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Default why is my 2006 Prius only getting 38-41 mpg?

I have a 2006 with about 60k miles on it. I've changed the engine battery and 1.5yrs ago.

For a couple years now I've been getting low mileage. I've never gotten 50mpg, but when I first got the car I would get at least 46...maybe 47. I live in SoCal, but only run air conditioner in summer and try to roll into stops and take my foot off the gas when going down inclines.

Would any type of tune-up, fuel injection flush etc.. help with raising fuel economy?

If so, is it worth taking it in to the dealership or would a general trusted mechanic due? Truth be told, i'm a bit apprehensive about taking cars to dealerships for service based on past experiences. However, if there is a specific service that the Prius experts at the dealership could offer that has a track record with improving mileage, I would go.
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post #2 of 5 (permalink) Old 02-27-2013, 09:38 AM
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There are a number of things that can cause reduced mileage. How is the air pressure in the tires? How is the oil level in the ICE? The level should be just below the full mark. High oil levels will reduce mileage as well as possibly damage the engine.

There is not much to tune up with the ICE. You also don't need a fuel injector flush as long as you have been using a good quality gasoline.

I'll bet that the first two items I mentioned are the cause(s).
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post #3 of 5 (permalink) Old 05-30-2013, 06:17 AM
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A couple of tips:

* Pump up front tires to maximum pressure printed on the sidewalls. Pump rears up to 2-4 psi less than the fronts.

* Accelerate briskly to 30-35 mph (nearly full throttle) to maximize electric motor use, then use cruise control to slowly speed up to 41-42 mph. If speed limit is 45, do not exceed 41-42 mph, as lights are usually synchronized at 40. Note: ICE usage is minimum at speeds less than 42 mph and with cruise control ON.

* Learn to drive with cruise control almost all the time; this will save gas. If you want to save fuel, the hybrid system computer is smarter than your right foot.

* On the highway, avoid passing, which requires speeding up, then slowing down, which wastes fuel. Pick a speed and use the cruise control for any speed changes.

* Anticipate traffic light changes from 1/2 mile away. Click down on cruise control to gradually slow down when approaching light and avoid using brakes. Use electric motor only or coast as long as possible, as this minimizes ICE use and saves fuel.

* If you have to accelerate, do it briskly. If you have to decelerate, do it slowly and coast as long as possible.

* Highest mileage is at 41-42 mph or slower, at constant speed, with heater or air conditioner off.

Last edited by Phoenix; 05-30-2013 at 06:19 AM.
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post #4 of 5 (permalink) Old 07-31-2013, 07:37 PM
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Default why is my 2006 Prius only getting 38-41 mpg?

It may be worth having the dealer check the hybrid battery.
I started having low MPG(low 30's) while I was normally get 41-45.
Also performance had been sluggish for a few months.

One cold morning the master caution came on and I was able to limp to a dealership. They found 1 or 2 bad cells in the hybrid battery.
These were replaced under warranty with no questions.

I have also had my share of 12v battery issues as the Tucson heat is notorious for killing 12v batteries. The hybrid and 12v issues look the same except the MPG issues are not present with the 12v battery issue.

2006 Prius, 78k miles
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post #5 of 5 (permalink) Old 07-31-2013, 08:31 PM
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Our mileage has been low this summer, too. I usually average of 42-46 mpg, with a peak of 48-51.5 in the spring and fall when the weather is nice. In the summer, mileage often dips to 36-38 mpg, but our Prius is currently getting 32 due to the summer heat.

Per our APS bill (Arizona Public Service, electric utility), this summer has been much hotter than the last couple of years (APS was $425 this month). Not sure about the 2006 Prius, but the air conditioner on our 2002 runs off of the ICE; and the last two months, the ICE runs almost continuously when driving. Thus, the low mileage.

I just replaced the traction battery, and we got our car back today. However, I doubt if the fuel economy will improve with the new battery. I accelerate full throttle off of every traffic light to maximize electric motor usage and reduce gas burned, so I am familiar with the combined electric motor/ICE acceleration characteristics; and there appears to be absolutely no difference in acceleration between the old battery and the new one.

(The failure mode for the old traction battery was "DEAD", i.e., no electric motor assist; and there was no gradual decrease in acceleration prior to the entire hybrid system shutting down.)

You might try using the driving techniques that appear in my previous post, the most important being to pump up the tires. Otherwise, I suspect we'll both just have to wait until October for fuel economy to return to "normal".

By the way, I have purchased 12-volt batteries from the company below on two occasions. The most recent replacement was an Optima Yellow Top, earlier this year. Their prices are very good, and I got one business day delivery in Phoenix, from California. I ordered the battery on Sunday night after midnight, and it was delivered on Tuesday at around 10 AM. Tell Bernie Littman that I referred you.

By the way, I have no affiliation with this company, other than being a satisfied customer (twice):


Note: See instructions on how to test your 12-volt battery near the bottom of this very long Web page.
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