very bad prius mileage

Are you giving us the MPGs reported by the car's display? Or are you calculating them manually? In a Prius the display is accurate to within a few percent, but manual calculation for a single tank can be off by a factor of 2.

You can safely go up to the cold pressure given on the side of the tire (44 PSI for the original tires). But you will notice a change in handling, so if you do this be alert.

If you use grill blocking and don't have a scangauge for monitoring engine temperatures, don't forget to remove the blocking in the late spring. It would be bad to improve your MPGs now only to burn up the engine valves later.

 

But your SUV probably costs you more than $12 to fill up My Land Rover used to get 300 miles on a tank, but took 23 gallons (of premium) to fill. Thats 13mpg, using almost exactly 4 times more gas than my Prius. Its important to remember that higher mpg = lower cost = fewer pounds of CO2 = less air pollution = less money going to terrorists. Miles per tank is at most an inconvenience, and fairly trivial by comparison.

You probably don't want to be doing much coasting/gliding when its cold. With the engine shut off, it will cool down very quickly particularly with no grill block. That means it will have to run longer the next time it starts to warm itself back up. In cold temps your best bet is to accelerate up to a reasonable speed fairly quickly, and then just hold it there and back off the pedal as much as you can and still maintain speed. Accelerating like a granny actually uses more gas. You don't want to floor it, the engine shouldn't really rev up much, but about 1/2 way down on the pedal is good. If you can watch the instantaneous mpg, it should be about half your speed while you are accelerating, 15mpg at 30mph, 20 mpg at 40mph etc. That should get you going quick enough to keep up with traffic, and get you up to speed using as little gas as possible. Driving 55 is a good idea though. On surface streets I find 35-45 to be a very efficient speed range. Slower than that and the engine will cycle on and off, causing the same cooling problem as above.

I'd also be careful about trying to top off too much. The cold bladder will only stretch so much, and overfilling can lead to expensive damage to the vapor recovery system. Its also important to keep things in perspective. In the cold my Land Rover would drop to about 10mpg instead of 13mpg. While 3mpg doesn't sound like much, thats 23%. On a Prius, the same 23% is the difference between 47mpg and 36mpg, an 11mpg difference! Because the Prius uses much less fuel, these kind of changes are greatly exaggerated. There doesn't seem to be any one thing that works for everybody. The best thing seems to be to try lots of different suggestions, and see what works best for you.

Good luck,
Rob

 

When I don't carpool my commute is ~30 miles. Except for rare occasions I lose up to .5mpg on the current tank's average over the 1st half of the trip. First, it has to warm up. (Today I saw 190F coolant temp for the 1st time in ages.) Second, traffic lights disrupt steady driving. When it is warmer I can recover the day's loss and add a bit as there are fewer lights and smoother traffic. The home stretch is a tour of the company's parking lot on electricity and a green battery to my parking space.

When I carpool the ride is ~15 miles. Losing the 2nd half of the trip is causing the tank's average to slide. Sometimes I can break even on the day but it is usually 1 or 2 tenths down.

The worst fuel economy I ever got resulted from the car sitting with the AC on in the blazing sun which ran the traction battery down before running on the autocross course. I couldn't have asked for the car to be in worse condition for the competition. With all due respect I don't believe your SUV's FE is that high.

 

Are you referring to 'amount of gas purchased" each fillup rather than the "miles per gallon" ? Your Prius computer will be your best guide for general use (especially with the bladder fillup issues) and if your SUV has a "regular" gas tank manual calculations are OK (miles driven divided by gallons used).
I have found it easier to work real hard to get the tank full one time and then regularly refill by half a tank used, which usually means 4 or 5 gallons and approx 220 miles driven. You also may want to research bladder concerrns and filling techniques on PC.
If you've followed suggestions from other posters and are getting worse "miles per gallon" than an SUV please take the Prius to a dealer for evaluation, something is wrong.
Good luck, I hope you can fix the problem so you can enjoy your Prius as much as I do.

 

Bullshit.

... Brad

 

For most people on this board....

Mileage = Miles Per Gallon (MPG)

Range = Miles driven between fill-ups.

I'm assuming when you say you get better "mileage" with your SUV, you mean longer range. (300 miles per tank vs 250 miles per tank).

Increasing tire pressure is easy to do with quick, measurable results. Don't let the "service guys" fool you. Max tire pressure is the way to go. Many studies demonstrate that and under inflated tire is very dangerous. Do a google search and you will find recommendations saying that filling to max sidewall psi is safe.

 

Each and everytime continue to try and strech the bladder. Its only a problem if gasoline is forced into the tank when gasoline burps back out. It wii be easier in summer.

 

Thank you, very much, for asking questions, listening to the responses and attempting to incorporate some of the suggested changes. Too many people in your position have simply complained and whined and not tried to make adjustments.

I'm certain you will continue to learn more about your Prius and how you'll be able to enjoy it even more by increasing its fuel economy.

Even so, I think there may yet be some misunderstandings going on here.

I live in a cold-weather climate, and I've experienced some pretty low mileage in very cold weather. I can't recall the lowest number of miles on a tank, but I can remember the lowest MPGs -- 35.0. I also remember the high MPGs -- 61.3. The lowest was in a very cold December; the highest in August. Temperature does make a big difference.


Here are some questions I have for you:

1. Do you keep a record of your gas purchases, the miles you've driven and any other information (price, temp, type of gas, station, etc.)?
2. Do you record the information from the MFD?
3. Have you kept records for your SUV?

I understand you don't like the fact you are getting more miles per tank out of the SUV than from the Prius. Still, have you compared how much you spend per tank or per mile? Have you added up all the miles you've driven and divided by the gallons of gas you've purchased? The MFD display is much more reliable than a tank-by-tank record, but when you look at the ratio of total miles driven to total purchases of gasoline, the MPG you find should be fairly close to the MFD readings.

If you need help getting this data to give you good readable information, there are several folks who have offered very usable spreadsheets that will report the results to you if you input as little information as what shows up on your purchase receipt and the MFD at the time you stop to fill up.

Please let me know if there is anything else we (meaning other PC members) can offer.

 

You can not rely on the 6.9 gallons you pumped to have made a full tank of gas...6.9 is just what the "incredibly shrinking" gas tank bladder will allow into the tank on that particular occasion. On a colder day or with a faster running pump it may be less than 6.9 or on a real hot day and a slow pump 8.9 gallons
What the screen says is what MPG you got for the gas that actually went through the gas engine.
When considering your MPG do NOT pay any attention to the gas pump reading. I think this bladder thing is causing you a lot of unnecessary distress.

 

In the winter snow I wouldn't go too high on the tire pressure
As for the the MPG do not keep your accelerator in one position, let up and allow the car to get to more electric then gas

 

I would have to agree that I don't think there is anything wrong with the OP's car other than cold weather. I'm getting much lower gas mileage now with the cold weather too. Yesterday I took a trip to Bismarck and my mileage was about 35mpg, when in warmer weather I average mid 40 mpgs on the same trip. Yesterday the temp was about -5F. I do have my grill blocked too.

 

Alright. I'll give a go to your questions, but I'm certain you'll find more complete responses coming later.

Where do you get the miles from? Two (well, three really) options. The first is the odometer (you also could use a trip odometer to give you miles to the tenth of a mile), and the second is the MFD. The miles reported on the MFD will be slightly more correct, fill-to-fill, because it zeros out. For the long run, I suggest you write down the odometer mileage as well.

How do you determine MPGs? Use all of the information available to keep mileage in two forms. The first is what is reported on the MFD. The second is what you calculate using the amount of gasoline you purchase.

For the first method (MFD info) you should track the miles driven and the reported MPG. If the screen (MFD) reports, for example, 220 miles and 36.2 MPG, write it down. Also, write down the calculated gasoline used. This number is calculated by dividing the miles (220) by the MPG (36.2) to give you 6.08 or 6.1 gallons. If the next fill-up comes after 240 miles and shows 35.4 MPG, then you put in that information, as well as the calculated gallons of gasoline as 6.78 gallons (or 6.8). This lets you figure out your combined mileage for those two tanks: 460 miles (220 + 240) divided by 12.86 gallons (6.08 + 6.78) for mileage of 35.8 MPG. If the next tank comes in at 180 miles at 28.4MPG (6.34 gallons), then the combined mileage goes to 640 miles/19.2 gallons or 33.3 MPG.

For the second method (purchased gallons) you should track miles (odometer reading) and gallons purchased. Your first purchase was was at odometer mile 5,220 (starting at 5,000, for example) and included 6.9 gallons (31.9 MPG - I don't know how you got to 28). The second purchase was at 5,460 and included 6.0 gallons, for which you calculate mileage of 240 miles/6.0 gallons or 40.0 MPG. The third purchase was at 5,640 for 7.3 gallons (you were getting nervous by now!) for mileage of 180 miles/7.3 gallons or 24.7 MPG.

You'll notice significant differences between the MFD and your gas purchases. This is very common (expected) during the winter when you have a non-expanding bladder. Don't worry about it.

If you look at the overall gas use by the second method, you'll find that you traveled 640 total miles and purchased 20.2 gallons. This calculates to 31.7 MPG. It isn't the same as the MFD, but then it covers only three tanks (full?). The 31.7 makes much more sense than the variation from 24.7 to 40.0 MPGs. You'll notice the MFD doesn't typically have such wide fluctuation, unless you are driving under different conditions.

You had another question: How and from where does the MFD mileage (MPGs) derive? I don't know the particulars, but a computer uses the same miles as shown on the odometer and divides that by the amount of gasoline calculated to have entered into the ICE's cylinders on a near-instantaneous method. Believe me: it is much, much more accurate than the assumption you are able to fill your tank to the exact same place, tank after tank!

I'm sorry if this is too convoluted, but I hope it helps you better understand the actual gas usage of your car. If you track this over the long haul, you will notice the difference between gas pump volume vs. calculated gallons used will shrink to a consistent variation (long term) of somewhere between 1 MPG and 1.5 MPG.

Keep up with the questions!

 

maya The screen that shows your milage in 5 minute stages and that bar that runs up the right side. Where is it when you are driving? I like to watch the screen that shows where the power is going and then toggle to the other to see how I'm doing. We took a 2500 mile trip from chicago to virginia beach 2 weeks after getting the car and the total trip was milage was 54mpg. I hardly knew how to turn on the wipers it was so new to me but watching that screen I think made the difference.

 

Maya, it's called the "Guess Gauge" for good reason and this is your initiation. Generally I find the MFD is optimistic and it's FE calculation within a couple percent of my numbers. However, at times there can be a 20% difference which is most likely during the winter but can happen any time. If you experience a very low FE tank next to a very high FE tank then you just experienced a fueling issue and it averaged out. So, don't get too excited on 1 tank.

I know how it feels to come here and read about "everyone" getting 50+ when you're stuck in the mid or high 40's. Improve what you can, accept what you can't, and learn to discern the difference. We can't change the climate or the terrain. We can experiment with routes and speeds. We can make small and inexpensive adjustments to the car that produce "huge" improvements. In my case the biggest adjustment needed to be done to the "nut behind the wheel". The Prius will teach you how to drive more efficiently. I listen to those who do better and adapt what I can. I may not be able to do as well as John, or Hobbit, or Evan but that's not the point. The competition is within. Now that I have x mpg what can I do to get x.2? I am sure that with your attitute and enough experience you'll get the lifetime average up to 50.

BTW, do you buy one brand of gas regularly?

 

Maya, "Patience, Grasshopper." I filled up tonight at 1 pip and 394 miles seeing 52.2 on the MFD & expecting 41. The car took 7.475 gallons at automatic shutoff for a calculated 52.7 on Sunoco. The previous tank was 48.8mpg and lifetime is 52.9. If I can hold 50 through the freezing winter I'll be happy.

I keep the climate control off for the 1st 5 minutes unless I can't see. Turn off the cc at a stop if the ICE (internal combustion engine) runs. Temp set at 72 and fan speed low on manual gets the cabin comfortable.

Different gas formulas and different pump sensitivity also have an effect. You just have to discover what works best for you.

Keep us posted.