Help - Bad mileage - why?

You have a near worst-case scenario: cold weather, short trips, and cabin heat in city driving (presumably with some stop-and-go). I'm not surprised at your results.

Any car will take a hit in those conditions. The effect is magnified in the Prius because when the Prius' ICE (internal combustion engine) completes its warmup cycle, it shuts off when not needed for propulsion. Your ICE never has a chance to complete the cycle.

Two things to consider that will help: grille blocking (cool weather only) and engine block heater (year 'round). Do a good search and you'll find plenty of discussion on both.

 

Jimbo is correct about the warm-up cycle. If you had additional instrumentation, you could see exactly when that occurs. However, I suspect you would only find it frustrating.

If you have a 3 mile round trip, that is 1.5 miles each way. Averaging 20 mph, it will take 4.5 minutes. That is probably not enough time to complete the warm-up cycle except in warmer weather, and then only just barely. If you run the heat at all, you will not get to temperature in such a short time. If you drive faster than that, you will already be there before the car is warmed up.

If you drive slower, say, 10 mph, you will reach the magic temperature in the middle of your trip. Then, the car can be driven to get very high MPG's, but I do not recommend this because a) you will have such a short distance remaining that it would not be worth it and b) it's nearly impossible to find a route that is safe to drive that slowly.

I do not recommend an engine block heater for you, because you are not close enough getting the car warmed up for it to be worth it. Certainly not in cold weather. I do not know how cold it is in Portland. Not as cold as it is here, I guess. You may still need to turn on the defrost if it is chilly and humid. I wouldn't expect grill blocking to put you over the threshold either, but it couldn't hurt and costs next to nothing.

You could say that your co-worker has an ideal commute for this car. If she drives 20 miles, even at 60 mph, that is at least 20 minutes. The car can be allowed to warm up and then driven efficiently. However, another way to look at it is that given her commute, she has the ideal car. Your commute is short enough that you use less gasoline than she does. You also spend less time in traffic and can leave later to arrive at the same time.

 

I had a similar commute to yours. The temperature here is not typically a factor. I drove about 6 miles RT - and at speeds less than 40MPH. This year I have a 50 mile RT mostly freeway speed. The MPG went from 36.2 to 48.1 That's about a 33% increase just because of the speed and distance.

The MPG would likely be greater than 48.1 if I could avoid driving at 65-75MPH on the freeway. That's not always possible, and mileage does suffer at those speeds.

So, yes, the combination of external factors like distance, speed and temperature are all combining to make your mileage less than you might like it to be.

At a 1.5 mile trip, it's almost worth looking into walking, riding a bike or taking the trolley in Portland -probably the best option this time of year (if it stops nearby).

 

To reassure yourself about the lemon part, have you checked mileage on a long drive? If your accumulated mileage on the MFD after say a 50 mile drive is in the 40's or better I'd say your car is fine.

As stated above short trips are mileage killers!

 

And don't drive in "B".

 

I too have had a similar experience. I bought my 2007 brand new going on 3 years ago. As Prius owners know, you have to "learn" to drive this car. When I first got it, I was getting around 42mpg driving as usual. once I got the hang of it (coasting more, not accelerating like crazy, etc.) I could keep it around 50-53mpg which I was perfectly happy with. The dealership (and toyota) advertised the car at 60 highway so a little disappointed, but fine with it.

For the first couple years I drove A LOT.. as in.. I have 76K miles and my 3 year anniversary is this summer. Obviously a lot of that was interstate commuting for work. Around October this fall, I moved right near my work and saw an immediate drop to 35 mpg. This really pissed me off but it seemed my particular route was to blame. It was about 5 miles, stop and go, red lights, <45 mph the whole time. All the lights seemed to be in a valley of a hill so I was constantly breaking on the downhill just to have to accelerate on the incline. What can you do??

So I just relocated jobs and housing again and now live 2 miles from work. I have the same driving conditions for the most part (no interstate, etc.) I got yet another drop to 28 mpg. I started to freak out at first and changed my air filter, tires, etc.. Then I read this post.

I understand the whole warm up cycle and yes, interstate driving would help, but I'm getting a little resentful of the Prius. At 28 mpg, there are a lot of other (cheaper) options for driving.

 

For comparison, my Subaru is rated 25 mpg highway, and my overall average is higher than that. But while warming up, its ScanGauge is showing horrible numbers. Your commute distance is at about the point where my Suby mpg rises out of single digit range.

Whether short trips or long, the Prius is roughly twice as good. Except in stop-and-crawl traffic, where it is about three times as good.

 

EPA tests, short drives

The "60 mpg" is all that Toyota and the dealer could legally advertise. Blame the old EPA test method. It was converted via formula to approximate the new method and the new rating is 48/45, 46 combined.

What tires did you change to?

Yes, you've figured out your short drives are killing your mileage. You should consider grille blocking but only when it's cold out and keep the heat off (just turn the fan off) if you're not doing acceleration that would need the ICE. If coolant temp is <=145 F, the ICE will run to provide cabin heat. As for "28 mpg, there are a lot of other (cheaper) options for driving.", those vehicles would very likely do much worse than 28 mpg in the same drive.

You would probably find http://priuschat.com/forums/other-c...uth-about-epa-city-highway-mpg-estimates.html insightful about what the EPA tests consists of. For instance, the old city test is 31.2 minutes long w/11 miles of simulated driving between 68-86 F.

For reference, Consumer Reports in their testing of the 2nd gen Prius got 35 city/50 highway, 44 combined. You can see how that stacks up the most efficient cars at Most fuel-efficient cars (Prius IV is the 3rd gen aka 2010).

I can lookup what CR got in their tests for these cheaper options you cite if they're not on the above list.

 

Was this a sudden drop in mileage? If so, there may be another explanation.

I have a 2008 Prius. In November of 2008, the mileage dropped by almost 50% to 26 mph. At the service station, I was asked if I had had to jump-start the car, as the ECU had "lost its settings". Here is the written explanation I was given: "The vehicle had history codes for the Gateway ECU. The monitors were reset to default system settings. The vehicle was driven 20 miles after a test drive. The monitors were reset and the system re-checked." When I drove it home, the mileage was back up to 48 mpg.

Since then, there have been two other episodes where the mileage dropped to about 26 mpg. These times, however, the ECU settings were normal at the service station.

Has anyone else encountered a similar problem? Is this something to be concerned about? A potential ECU defect?

 

Every other car would get less than 28 MPG under the same conditions. And keep in mind that the *absolute* amount of fuel you are using per month has decreased drastically even though the per-mile figure is worse.