Comparison: 2 prius's 1driver very differnent MPG??

[Joey40202]

Hello to All,

I have a 2007 package #3 touring prius in graphite gray.
Here is my current configuration:

• 44psi in all tires
• no dead weight in the car
• driven with the windows up 95% of the time with the ac on and I minimize the ac once the vehicle is cooled
• Coast to stops

I am exeperiencing a few problems with my fuel economy.

Driving conservatively I am only able to average in the high 43 to low 44MPG range.

For the past two months I was out of town and I gave my father who is also a prius owner my prius to drive to see if he could improve the mileage. My father has a white/2008 package #2 (mine is a charcoal gray/2007 Package #3 touring).

My father logged just ove 2,500 miles on my vehicle while I wasout of town. While my father was driving my 2007 prius my mother was also driving the 2008 prius for the two months which I was gone. All the variable are constant except the vehicle are different.

He drove the same routes, drove in the same manner, used the same gas stations, ran the a/c at the same intervals and speeds as he does in his own prius.

The difference is as follows: The 2008 prius is getting 49-50MPG and my 2007 is getting only 44.5 avg MPG. All the variables are the same except the actual vehicles.

***Also, My father and I traded vehicles for a month and I was able to maintain the 50 MPG that he was getting and I actually was able to improve the MPG up to 52mpg at one point. I have noticed that my 2007/gray prius has a significantly weaker electric motor assist especially when trying to accelerate from a stop. It is extremely difficult to get the electric engine to stay engaged in my 2007/gray prius.

In comparison my fathers 2008/white prius not only is able to accelerated from a stop but once up to speed he is able to let off the gas petal and reengage the electric engine up to 38 mph before the gas engine takes over or the the battery pack is exhausted which ever comes first.

My 2007 prius appears to spend most of its time trying to charge the batteries and has little time where it is actually running on electric of the batteries. I feel like the is a problem with the electric assiste system but techs at toyota said it was fine and it was a result of a/c running more due to the darker color of the vehicle.

I consulted my father about what they said and he said he ran the a/c at the same intervals/temp/duration as he did in his own vehicle so I am skeptical of the toyota techs theory.

Does anyone have any ideas as to what might be causing my problem with fuel economy? Or has anyone had the same problem(s)?

Thanks in advance,
Joe

[uart]

Hi Joe. I would try two more tests before worrying about the main battery.

1. Check the odo on the 2007 against the 2008 to make sure they are both reading the same (as this can obviously make a difference to the apparent fuel consumption).

2. Do a few manual fuel consumption calculations for each Prius (distance travelled and gas used at the pump) to make sure that your MFD figures are reasonably accurate. I just found out that the MFD displayed MPG on my 2004 prius is quite a bit less than the actual MPG, though apparently this is pretty unusual.
BTW. When doing "at the pump" tests it helps if you average over a few tanks to improve accuracy.

If the consumption figures are accurate then perhaps it really is that your battery is not as strong as the other one. Someone mentioned in another thread that if the auxiliary 12 volt battery is in bad shape then the main traction can waste a lot of power trying to keep it charged (through the inverter). Honestly I don't know how relevant that is but it might be worthwhile getting the little battery checked out first.

[drees]

One's a touring the other isn't.

The touring will always take a bit of a hit due to the bigger wheels/tires.

Try swapping wheels tires for a while and see what happens. Also, as uart mentions, calculate the fuel economy manually for at least 3 tanks, preferably 5+ and double check that the odometers are calibrated.

What tires do you have on each vehicle and how much tread is on them?

[donee]

Hi Joey...,

I concur with Drees. The 2007 Touring car has the 16 inch wheels/tires, which are wider (as air volume in the tire sets the load rating, and the load rating has to be the same or better between wheel/tire combinations). The wider tires have more patch area, better handling, and more rolling resistance.

People who swap out their 15 inch tires for 17 inch see even lower fuel economy.

[Joey40202]

"

Originally Posted by drees

One's a touring the other isn't.

The touring will always take a bit of a hit due to the bigger wheels/tires.

Try swapping wheels tires for a while and see what happens. Also, as uart mentions, calculate the fuel economy manually for at least 3 tanks, preferably 5+ and double check that the odometers are calibrated.

What tires do you have on each vehicle and how much tread is on them?

"

I forgot to mention that the manual MPG calculations was calculated over a few tanks and they are both within .5 mpg margin of error between the odo and the computer.

The tires and wheel combo on the touring I have taken into consideration but I still cant fathom the 5-6 mpg difference between the two vehicles. My understanding was that the touring would reduced the mpg approx. 2mpg due to the larger wheels?

The tires on my 2007/touring are aftermarket tires and they are new with in the last 3,000 miles. They are Toyo Proxes T1R tires.

The 2008/white prius has the original factory tires and have approx. 15,000 miles on the tires.

The treadwear idea is something I overlooked. Although I was expecting to have a lower MPG due to the larger wheels.

Although the wheels are adding to my MPG issues I still feel like I am having a serious issue with the motor running on electric. Last night I was in my 2007 prius and I paid specific attention to when the electric motor was engaged based on the info screen in the car.

What I noticed is the car rarely ever registers the 99.9mpg even with my foot isoff the gas and the car is coasting? While coasting the batteries are also being charged back up (which I know is a regular process) but then if I try to initiate the electric motor assist below speeds of 34mph it is extremely hard to get the electric motor to kick in and almost impossible to get the vehicle to mantain a electric cruise for any period of time which is something that is able to be achieved in the 2008/White prius.

Does anyone have any thoughts as why this could be?

[donee]

Hi Joey....,

The newness of the tires supports the greater difference. My opinion is that allot of the new-car improvement in mileage is due to tire break-in. When I got Hydroedges at 5000 miles, it was like starting with the car from scratch. Although at 3000 miles most of the break-in should be over. Do you know any rolling resistance specs for these tires? Are they summer performance tires (softer compounds of rubber - more rolling resistance) ?

The comments regarding having difficulty getting the car to glide (no-arrows coasting in transmission D mode) or stealth (electric cruise) also support the tires as the source of the mileage issue. What road-toque is permitted to be powered by the battery alone is dictacted by battery SOC and temperature. So, its not complete evidence the tires are the problem.

[uart]

Originally Posted by Joey40202

""
What I noticed is the car rarely ever registers the 99.9mpg even with my foot isoff the gas and the car is coasting? While coasting the batteries are also being charged back up (which I know is a regular process) but then if I try to initiate the electric motor assist below speeds of 34mph it is extremely hard to get the electric motor to kick in and almost impossible to get the vehicle to mantain a electric cruise for any period of time which is something that is able to be achieved in the 2008/White prius.

Does anyone have any thoughts as why this could be?

I'm not totally sure but I notice a similar thing when I'm coasting/gliding. Most of the time the engine cuts off and I get 99.9 (actually I get 0 L/100km but it's the same thing) but every now and then it keeps the engine running while I'm gliding. Not sure why but it's certainly not every time. Are you saying that yours keeps the motor running every time you try to glide?

If I were you I wouldn't try too hard to make it engage all electric mode in regular driving. I've found I'm mostly better off to keep the charge on the battery and just let it use it for assist up hills or slow start stop driving. Having said that I can usually coax mine into all electric mode pretty easily on terrain that's flat to very slight downhill by just backing the accelerator right off for a few seconds and then re-applying the gas very lightly. This will usually make it engage all electric mode, at least for a while, especially if the speed is below about 40 mph. Like I said before though, I've found it's better not to coax it into this mode and run down the battery as the motor just has to work harder later to make up the lost charge. I like to use that mode only when the down hill is steep enough to give some gliding and some regeneration too, so the motor can stay off for a while but overall the battery is not run down.


Try driving it for a while where you're not really trying to get it into all electric mode and see what happens. You might find that by keeping more charge on the battery that it will start going into all electric mode more readily when you really want it to (as in where it's really useful like real downhill glide + motor + regen combo).

[drees]

Comparing stock vehicles (meaning stock tires), the touring Prius is down a couple mpg compared to the regular one.

Now add sticky, ultra high performance summer tires like the Toyos you've got and subtract another couple mpg.

Voila - there's your 4-5 mpg difference.

[uart]

Originally Posted by drees

Comparing stock vehicles (meaning stock tires), the touring Prius is down a couple mpg compared to the regular one.

Now add sticky, ultra high performance summer tires like the Toyos you've got and subtract another couple mpg.

Voila - there's your 4-5 mpg difference.

Yep just take a look at the tyre test posted here last week :
Tire Rack pits Integrity against Energy Saver, Ecopia and Fuel Max

Up to almost 8% difference in just the limited range of tyres they tested there.

BTW. Can someone please help me understand why the touring Prius is generally a couple of MPG down compared to the regular package. I always thought larger diameter tyres would give a slightly lower rolling resistance. Are there some other additional differences that account for this?

[usbseawolf2000]

Originally Posted by uart

BTW. Can someone please help me understand why the touring Prius is generally a couple of MPG down compared to the regular package. I always thought larger diameter tyres would give a slightly lower rolling resistance. Are there some other additional differences that account for this?

Touring edition tires are wider (185mm vs 195mm) so there are more contact area with the road; therefore more rolling resistance.