Very Poor Acceleration Gas Mileage

There are a lot of posts here that can help you improve your gas mileage.

IMO it helps to know what your last car was or what your other car(s) is/are? In my case, the other car is a Chevy Blazer. If you don't have your foot on the acc pedal, it will slow down pretty quickly. The Prius just kind of glides with just a feather touch on the pedal.

Also, did you buy this car from a dealer or a private party? As with any car, accelerating quickly does burn more gas than just cruising along. If you bought it from a private party, you might want to take it to the dealer to make sure all is up to snuff.

Finally, how long are your trips? The Prius takes awhile to get warmed up. If you just drive it a mile or two, then go into the store and then drive it home, mid 30s may be all you ever see. That's been one of my friend's experience. I take few trips of less than 3 or 4 miles with a lot of 16 mile trips (commuting) and get lower 50s.

Of course, I would have been happy with 36 mpg since my Blazer and the S-10 pickup that the Prius replaced average 13 and 14 mpg!

 

First thing to check is to make sure the parking brake is disengaged.

 

Since we know nothing about your drives, driving conditions, length of trips, etc., it'd help us a lot if you'd copy, paste and answer the questions from http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html.

FWIW, Consumer Reports in their testing of the 2nd gen (your generation) Prius gave it a 35 city/50 highway, 44 mpg combined and it most efficient car they tested at the time that was still available. You can see how that compares to others most efficient cars at http://web.archive.org/web/20080618...-advice/most-fuelefficient-cars-206/index.htm. Let me know if you want me to lookup their mileage test results for a car that didn't make the cut.

Yep, if you trips are short (say <10 minutes) w/no highway driving and esp. if the weather's cold, you're not going to break 40 mpg. Since your car has 90K miles, it's almost a certainty that it doesn't have the factory tires anymore. So, please be sure to include what you have as part of answering the questions.

 

Hello Hokie. There are two separate issues involved here, low instantaneous MPG and low overall MPG. First let me say that yes it is fairly normal to sometimes have instantaneous MPG's that are quite poor when accelerating, particularly at low speed, and this does not necessarily mean you'll get bad MPG overall. Personally I don't think I've ever gone as low as 2MPG instantaneous, but certainly I can go down to about 5 or 6 MPG when accelerating at low speed, yet I always average better than 50MPG over a tank.

Essentially all cars have the ability to output an instantaneous power which is much larger (typically at least ten times larger) than the average power required over a full journey. This large surplus power is required for things like acceleration overtaking and climbing steep hills. So all cars can get instantaneous MPG's down around one tenth of their tank-average values, it's just that most cars don't display this info.

The instantaneous MPG figure can also be a bit misleading, especially at low speed. It's important to realize that the actual time rate of fuel consumption (like gallons per hour for example) is equal to the reciprocal of MPG multiplied by the speed in MPH. In other words, 15 MPG at 10 MPH actually uses less fuel per second than 55 MPG at 40 MPH! The limiting case of this is when the car is at idle (cold with the engine running), where you actually get 0 MPG! Of course if you ran all the time at slow speed with the engine running you would get terrible fuel economy, but in practice you wouldn't normally drive a very large proportion of your total distance like this.

The last point I'd like to make is that having the HV battery in a good SOC (state of charge) can definitely help to battle those really low MPG figures when accelerating (or climbing small hills). I think the engine is able to maintain a more efficient operating point when there's enough electric power available to give a boost in high demand situations. What this means as far as good driving habits is that you're best not to try too hard to keep it running all electric, not if it means dropping bars on your SOC meter, unless you're going to be travelling down hill immediately afterwards.

 

Yes a poorly performing engine would cause worse fuel consumption, but so would many other factors such as :

- Tire Type
- Tire Pressures
- Wheel Alignment
- Brake drag.
- Wheel bearing condition
- Poor battery condition (either the main or the auxiliary).
- Driving style/habits.

 

uart makes good points. Since you just put out some bucks, you might start with the cheaper ones like driving style/habits and tire pressure first. Even if the more expensive issues remain, you'll still come out ahead.

 

At 90k miles, you need to change engine air filter. Spark plugs need to be changed at 110k miles.

 

Easily overlooked and as important as the air filter and spark plugs is the MAF Sensor. All DIY items. A search on PC will provide abundant info on these procedures.

 

and also PCV valve. This is how mine looked when I changed it at around 100k miles.

 

While we are on the subject: where is the PCV? and to test, I believe air passes in one direction and not the other, like a diode, right? Nice photos.

 

Didn't see the battery mentioned, it it's original it should be replaced, preferably with an Optima yellow top(search for the kit to install it), constant charging of the battery will kill mileage.

 

The guide is available here:

http://priuschat.com/forums/knowledge-base-articles-discussion/56852-pcv-replacement-how-photos.html