I'm getting low mpg on my 08 prius :(

wow... long thread. if you're comfortable commuting at your speeds, go ahead. keep doing that till around 5k miles or so.. that guarantees you a good break in period for the engine. i really think that makes a big difference

when you get to a higher odometer reading you can rev your engine and accelerate a little heavier. as some have probably said here... the key is to not using the battery. have your slow downs power the cars accessories.. and accelerate without battery help. I use EV till 10 or so mph... i feel it takes only a tiny amount out of the battery and i tend to regenerate a little more than the car needs. I've been testing with higher EV speeds and feel i should keep it low. i also use EV while warm up when i want to glide... or if i need to make a u-turn after starting up.

 

I have always noticed a significant change in mileage based on the time of year here in California. The gas in changed to meet the air pollution requirements. In both of my cars (Prius and Mustang) the mileage now is decreased about 10%-15%.

 

I here you. I just got my 08 and have about 1000 miles on it. The car says I am getting 55miles per gallon average but when I check it the old fashioned way it is only getting 42 mpg. The dealer and Toyoto were no help. The dealer offered to read the manual to me and Toyota said the readouts are only an estimate. Anyone else checking the real mpgs?

 

Two points: 1) Are you resetting the MFD screen on each fill-up? Otherwise its giving you the overall mpg, not just for this tank.
2) The MFD is known to vary from the computed, but mostly that's because the tank doesn't fill up to the same level each time, because the tank is actually a flexible bladder, and due to differences in the pump and click-off points, etc. (In theory, the MFD is more accurate because of these reasons. Others may disagree.) So for the MFD or hand computations, you really need to average them over several tanks to be sure, and they should come out pretty close (within a % or 2, usually). Your difference is pretty dramatic, but it's a new car, I'd put a couple more tanks on it and see if it averages out before getting too concerned.

 

08 pkg 5, 42/40 tire pressure, Cruise control at speed limit on hwy.
6900 miles (3500 on hwy mostly Interstate)
overall mpg 51.08 computed/51.45 MFD Hwy 49.9 computed/49.4 MFD

 

Hi Lori G,

The fill up volume of the tank is quite variable on a Prius. For example my last two tanks. Tank 1 had an MFD of 65.9 mpg (about 550 miles), but a fill up mileage of 53 mpg. Tank 2 had a MFD of 68.9 mpg (about 670 miles), but a fill up mileage of 73 mpg. The various gas station fuel pumps will click off at different back pressures. Also, the pump rates will vary with the the number of cars fueling at the same time as these pumps are all run from by compressed air power, and the compressor might be low if allot of cars are fueling att he same time. A slower fill rate will allow more gas to get into a Prius before the pump clicks off. Filling up after the first tank the pump delivered gas quite slow, and I apparently got allot more gas into the tank than normal. Which gave me another 100 miles range down to 2 pips (where I fill up).

Several people have done studies, where they did long term MFD and Pumped Fuel mileage comparisons, and found the MFD to be accurate within a few percent. Its easy to do, just back calculate the gallons consumed with the MFD reading and mileage on the tank. And talley the overall gallons and overall miles seperately. The variation is reasonable in that the MFD is measuring fuel volume, which can have different fuel energy content depending on the temperature. And the gas station pump is supposed to be measuring the volume of a constant 55 degree F fuel coming out of the ground.

 

OK, so here's the question. How much should tire sizes affect fuel mileage? I have a lot of gravel/rock/dirt roads I have to drive on here in Arkansas so I put new Kuhmo 205/60 15's on my car to gain a little more height and get rid of the (worn out at 20K) original tires. I love what it does for the ground clearance and hi-beam range at night but have taken a 10-12 mpg hit on mileage. Still at 42-40 tire pressure and I expected to lose 2 or 3 mpg, but 10-12 seems a bit much.... jf

 

I have a 2008 Prius, package 2 regular (non touring) model. Before I bought, I researched for a couple of months ... this site John's Stuff - Toyota Prius and more is about the best place to get lots of info.

I track everything about my Prius on an active spreadsheet, with calculations to tell me everything I want to know. I reset my trip computer for every tank of gas so I know what that tank is doing, the spreadsheet gives me lifetime data.

The day I bought my car, it was reading about 44 mpg when I drove off the lot (7 miles on the odometer) and by the time I got home, it was above 50. My lifetime total mpg for 6000 miles (in 3 months) is 49.8 something. This is including a couple of freeway trips of 200 miles at or above the speed limit ... and the mileage never dropped under 51 on those trips.

I have learned that brand of fuel DOES make a difference ... sometimes as much as 6 mpg from off brand to major brand. So far, Exxon and Shell have been the best for me.

I have also learned that outside temperature makes a BIG difference on mpg. Above 105 and my mileage drops to about 44-45, ten degrees cooler and it is above 50.


In reading your post, I see several items which can drop mileage. Let's take a look.

You say you have the touring model ... which means you have the 16" wheels and wider tires. Those tires will eat about 1.5 to 2 mpg compared to the tires on the non-touring model.

Tire pressure ... on my car, the difference between the factory 35 psi and my 44 front/41 rear is about 2 mpg.

Warm up. I have found that the first 1.5 to 2 miles of the day ... my mileage is poor ... my display number sometimes drops a full mpg until I get up to heat AND speed.

If I am driving and trying hard to squeeze the mpg ... or if my wife is driving ... and not trying to squeeze, my mileage still is above 52 mpg most of the time.

You are putting very few miles on your car and doing so in very short trips, your car isn't even broken in yet. As I add on the miles, my mileage keeps getting better.

I don't know your driving habits but how you drive can make a huge difference in mpg. Using the 2 second rule versus tailgating can make a difference of several mpg on any car, including the Prius.

I plan on switching to Mobil 1 oil on my second service ... at 10,000 miles. That should give me another 1 or 2 mpg ... based on experience with other cars over the past 20 years.

One more thing. I sometimes see posts where someone says they get so many miles per tank. THERE IS NO SUCH INDUSTRY STANDARD AS MILES PER TANK. Mileage is always in MILES PER GALLON. Miles per tank means squat.

Hope this helps.

 

More height/greater clearence implies greater diameter tire
Prius std oem tires = 24.4" over all diameter
>dia. = > circumference
>circumference = less tire revs/mile
less tire revs/mile = MFD sees longer mile, inaccurate
MFD calcs less mpg due to inaccurate mileage readings.
This also affects the odometer reading. Up-side, Extends the mileage limit of your warranty. Down-side ??? MPG. The old hand calculation won't work either since it's the mileage readings that are wrong. You could calculate a conversion factors for mileage and mpg to apply to your results. Or, I believe the SGII has an adj that will effectively compensate. I know you can adj the mph. I'm just not sure if it does it at the wheel revs/mile level or at the mpg calc level. If it's at the mpg calc level; it will only adj mpg and not any of the mileage readings.
The prius may have a method of adjusting it through a mechanical or progamming change. Other cars usually can be changed with a change to the gearing of the instrumentation that monitors the wheel revolutions.
Other affects of changes in tire size are more difficult, if not impossible, to quantify. Width, height, and profile affect the tire footprint's size and shape thus affecting rolling resistance and efficiency. Diameter also affects the relative gearing ratio between the CVT and the wheels, which will affect mpg.
Probably more than you wanted to know. Enjoy the "ground clearence". That's one of the things I liked about the original 2 VW beetles that I owned. Great for getting me back to those remote fishing and hunting spots.
Good luck with your new wheel/tires.

 

We just got back from a week vacation on the Cape Cod area and clocked in about 1700 miles round trip. The MFD says an average of between 54 to 55 mpg, but after doing some calculation my mpg is around 50 to 51 mpg. I think it is really close, so I am not very concerned about that. I had my AC on all the way and running at about 65 to 68 mph on the interstates....the Prius did well over all.

 

OK... I can breathe a little easier now... First of all thanks to those of you who tried so solve my problem. It turns out (I think!) that the computer was hung up on a low number.... 36.6.... and it stayed at that number almost 3 days before I noticed it. I noticed it looked the same and re-set it today on the way home from Church and either that fixed it, or we have a miracle
Getting 53 all evening. Perhaps the new size tire messed with the computer's mind or something. Anyway, I'll watch it a few more days to see how things are progressing. Since I drive 100 miles a day, it shouldn't take long.... jf

 

Just to chime in but I am seeing a similar problem. I have a brand new 08 Prius also pkg 6 and am only getting a high of 36 mpg. I also own a 2003 Honda Civic hybrid with 98,000 miles on it (original owner). I average 45 mpg in the civic and don't drive it hard. I also don't try and get the very best mileage either. When I do that it goes up to 50 mpg. So, I am concerned that despite driving very gently in the Prius I am getting enexpectedly low mileage. Yes, the A/C is on automatic and set for 72 degrees. I have it set the same in the Civic. But, in the civic when the engine turns off so does the A/C. I do notice the engine runs continuously after starting the Prius and I never see it shut off. Is this a problem? Is it only happening in 2008 models? I only have 300 miles so far so haven't needed to go to the dealer yet. I made my wife get rid of her 06 Acura TL which she loved and she is highly pissed at me now. We are getting ready to move to Hungary and the registration fees for the TL were $21,000 and for the Prius only $800 (there is a heavy penalty in Europe for poor mileage and large engines). Anyway, do I need to get the car looked at or is this usual during the first several thousand miles?

 

My opinion only... and there are far more qualified people here than me.... Is that the low mileage and unfamiliarity of how to hypermile are your problems. I drive with the screen set to the five minute incriments and try to keep the bars as close to the 50mpg as possible all across the screen. Learn how to pulse and glide to get best mileage in the Prius. Doesn't make normal sense, but when you give it the gas and quickly get up to your cruising speed, you are using both motors (better than one) and then when you back off and let it glide, you will be able to get the current reading bar all the way to the top. The more you can do that, the better your avg. will be. If your readings are in the 30's as mine was, I would re-set it and tell it to re-think the whole thing.... Good luck overseas..... jf

 

If you only run short trips, less than 5 minutes or so, you might never have the engine shut off. The engine will generally run until it is above 146 (?) degrees, it will also run to heat up the catalytic converter. However, even if the systems are not warmed up, if you stop long enough the engine should shut off. If this is not occurring you should take it into the dealer to have it checked out. For the AC, try setting it to auto at 79 degrees, you might be suprised how well it works set that high or even higher.

 

(condensed)

08 package 2 with 300 miles on it here. It is averaging just shy of 46 mpg. Same basic latitude and should have similar weather. (Commute is 6 miles each way in town, very hilly, several lights, plenty of traffic, some highway. Other mileage is mix of city and interstate/highway.)

The engine running continuously doesn't sound right. I noticed at high blower settings the engine was running much more. I crank up the blower for initial cooling when I need it, then set it down to a low level for comfort once the original heat has been knocked down. Your temperature set point sounds a bit on the low side to me and it may be keeping the AC compressor maxed (that is merely a guess on my part.) That might require the engine to run at an inefficient minimal level continuously.

When I'm sitting at lights the engine is off with the AC running on low. On down slopes I mostly keep the engine off, regenning if traffic/signals suggest I will need it, but gliding or using electric traction when possible. In the last 1/2 mile to/through the subdivision I can run almost completely off of electric with minimal regen.

I'm not a slow poke and so far it appears the car responds best to accelerating moderately quickly (lucky for me) in this terrain then gliding once up to speed. When my wife or I drove it tortoise like the mileage was worse and the engine was on more.

 

It sounds to me like you're driving the car okay, but I bet you have short trips. With the A/C cranked, the engine has too much load to turn off. I assume you just set the temperature and left the rest of it on auto, so eventually when the A/C drops the fan isn't on max anymore. At that point the engine will turn off (but the A/C keeps going) as needed. Or it could be the engine really is turning off, but you can't hear it with the fans going.

In any case, I think it's the A/C use and short trips giving you the poor mileage. Take it out for a longer run on a cool evening and see what happens. (And hit the reset button on the MFD after a fillup).

You know the auto setting basically does that for you, right?

 

Just a thought after reading several posts alluding to the fact that the Prius gets it's lowest, still great but lowest, mileage during short <3 miles trips. At the risk of being sacreligous here on PC. The Avalon will shift to our second car and spend most of it's time in the garage. However, as a believer of use it or lose it, we plan to try to use it at lease once a week. Where we live, all of our daily/weekly errands, shopping needs, are usually within a <3 mile radius. That said, it sounds like our local weekend shopping, groceries, bank, eating out, etc., would be a good time to give the Prius a break, and give the Avalon it's weekly exercise. Of course, we would miss the attention.:humble:

 

The wife's been adjusting that, thought she had it in auto. I didn't care for the result comfort wise (too hot) or economy wise (too low) so have been manually adjusting it for better results. I'll take a look at auto again once I get a better feel for the system.

 

Two more quick checks for borschelrh: check oil level (seems I've read here that high oil level can reduce mileage), check tire inflation. These aren't related to the particular symptom mentioned but are worth examining.

 

Thanks, I'll check the tire pressure. The tires appear fine on visual inspection. The car is new so shouldn't need oil (and I would assume the dealer checked it) but I will check that as well. Nearly all of our trips have been over 30 miles so it isn't the short distance syndrome. I haven't filled it with it's first fillup yet so maybe it is just a problem due to it being new. I did rest the MFD at the dealer. It started out at the dealer at 32 mpg (beltway to home, 65 mph) and we have slowly gotten it up to 36 mpg by driving it very carefully. I am just at 375 miles and the tank is nearly empty (although I understand that this isn't reliable?).

My main point is my 03 Civic hybrid normally get's 48 mpg despite my not driving differently from a normal car. If I really lead foot it I get around 43 mpg. That is the extreme low for me. I drive to work on the beltway and normally maintain 75-80 mph and get 48 mpg. I was expecting the Prius to be better than that. It seems to me that for the Prius to get even reasonable mileage you have to really drive it tenderly. I don't have to do that in the Civic. Also, in the Civic the A/C completely turns off when the engine does so that is perhaps a better thing. There is no way my wife is going to have a car that requires a 79 degree temperature just to get good mileage. So far I am not impressed with the Prius and am getting that sinking feeling I just wasted $28,000 dollars. I was really unimpressed with the dealer (Darcars, Silver Spring, MD) and am dreading having to try and get this resolved there. I live in Springfield, VA but work in Silver Spring, MD. Does anyone have any experience getting service at a dealership other than where you bought it? I am worried this will be a problem.

On a side note: Does anyone know if the warranty extends to Europe? I couldn't get a straight answer from the dealer. He "thought" it would be okay and that the Warranty is world wide. We are moving to Hungary and bought the Prius to avoid the huge registration fees for cars there. We had an 06 Acura TL and it was going to costs $21,000 just to register it. The Prus is around $800 which is why we bought it. We bought it here as the European version is a bit over $48,000 (exact same car) which is why Toyota has cut the numbers coming to the US. So, it will cost a lot less just to ship it (it will fit easily in the same 40 ft container along with our furniture and the toal cost will be around $13,000 to ship to Hungary. An additional tidbit, Gas prices in Europe typically have run 4x as high as the US. But, interestingly their prices didn't go up with the big increases in cost per barrel of oil. I can't explain that. But, today's prices in Hungary are 317 Forints per liter ($2.00 per liter) making a gallon of unleaded $7.62. So, I am really hoping to get the mileage problem sorted out. We are retiring there and don't need the car for shopping or local commutes. We will only use it for major shopping trips (nearest large city is Vezprem at 6 miles away) and for long vacation drives. I ski a lot (I work as a Ski Patroller and Snowboard Instructor in the Winter) and good ski areas in the Alps are only 120 miles away. We are dumping the Civic at $13,000 to a friend when we actually fly out next Spring. I would take it to Europe but will be surprised if the batteries last past 100K.