Is Prius two(of four) a loser?

She doesn't have the underneath cargo storage area filled with bricks, does she?

 

Try trading cars for a while. That should eliminate or verify the driver issue.

Tom

 

Specifically, if I were you, I would take the time and effort to have one of you--probably you--be in charge of all fueling and maintenance of the cars, at least for the duration of the experiment to try to get to the bottom of this.

Go to one single gas station, and go to one single pump at that station. See what the two cars show then. Gasoline can easily mean the difference between bad and good mileage.

 

Hi Arnie,

Just to be complete. You know the 04/05's automatically reset the MFD mileage at fillup. The 06 and newer cars require you to hit RESET on the MFD when you fillup to get mileage for that tank. Otherwise you get the mileage for the car since the computer was last rebooted (12 v battery disconnected I believe). Most likely in your wife's car, that means that mileage on the MFD is the average since the car was delivered to your wife.

 

Given two cars with different performance, I would approach this problem by:

1. drag measurement - use a gentle slope onto to a flat to measure how far both cars roll from a dead stop in "N".
2. ICE efficiency - more difficult, this requires instrumentation to evaluate the specific fuel consumption. You'll need a scangage or equivalent.
3. total energy monitoring - a bit advanced, this requires adding instrumentation to measure AC compressor and 12VDC accessory loads. Clamp-on current sensors and a data recording computer would be needed.

The first test, a hill roll test, is pretty straight forward if you can ensure both cars are at similar starting temperatures. You'll need several runs with both cars making sure the starting temperatures are identical:



If you do an operational temperature test, try to have both cars run about 20 minutes following the same protocol before the test. My data suggests it takes about 20 minutes before the transaxle oil reaches a stable temperature value. Of course, you could also get a four-wheel alignment test for each car.

Measuring ICE specific fuel consumption is a little more involved. You'll need instrumentation to read: (1) MG1 torque, ICE rpm and either air grams/sec or injector timing. With the first two elements, you can calculate the ICE output power and times the time interval, the Joules. Then using either air grams/second or ICE rpm and injector timing, the fuel consumed. This allows you to measure how much energy you are getting per unit fuel:




However, if you have identical hill roll and alignment test results and no instrumentation, the alternative is to run a maximum acceleration test. The protocol is a lot of fun:

1. Warm-up each car with a 20 minute drive and full tank. Identical vehicle weight with payload and passengers is important and getting the cars weighed would be recommended.
2. On the shoulder, hold down the brake and floor the accelerator to force-charge the ICE. Hold this until the battery is at max. A flat section of highway with little traffic is recommended.
3. With no traffic around, pull onto the road, hold the brake and floor the accelerator.
4. With a stop-watch, release the brake and measure the time to a high speed. Alternatively, mark the speed at a given reference.
5. Re-run the test at least three times, the same way, with each car to see if one vehicle lags the other.

If the drag and ICE tests show the cars are functionally identical, the only thing left is to find out what else may be draining energy. This requires a lot more instrumentation and we can discuss this after the simpler tests.

Bob Wilson

 

Gas both up.

Reset both.

Then trade for an entire tank. Let no one else drive that car for an entire tank.

Then see where you are.

Then you're looking at not only driving style but also where you drive. Does your wife do more short runs? Does she drive more hills? More freeway driving?

 

<div class='quotetop'>QUOTE(bwilson4web @ Jul 15 2007, 04:54 PM) [snapback]479321[/snapback]</div>

I was thinking wheel alignment, front and rear. If this is the problem, then it should show up in Bob's drag measurement test. Once you observe that the 06 does have more drag, you can take it to a frame and alignment shop and ask them to inspect the front and rear alignment, brakes or anything else that might have an influence on drag.

I am assuming that the four Prii all have similar stock rims and tires. If the 06 has upgrade tires and/or rims, that could be the root of the problem.

 

<div class='quotetop'>QUOTE(arniesalsared @ Jul 15 2007, 07:18 PM) [snapback]479327[/snapback]</div>

Start with the rolling test first. It is amazing how alignment issues can show up.
<div class='quotetop'>QUOTE(arniesalsared @ Jul 15 2007, 07:18 PM) [snapback]479327[/snapback]</div>

That chart is from my rolling hill test. I was comparing the original transaxle oil performance versus a fresh change. I was also testing the impact of cold weather on rolling drag with the only change being the transaxle oil.
<div class='quotetop'>QUOTE(arniesalsared @ Jul 15 2007, 07:18 PM) [snapback]479327[/snapback]</div>

If you are using a micrometer or caliper to measure the tread depth, I would be interest in the numbers. My experience has been that without accurate measurements, it is too difficult to really tell.
<div class='quotetop'>QUOTE(arniesalsared @ Jul 15 2007, 07:18 PM) [snapback]479327[/snapback]</div>

I'm interested in your results, payment enough. <grins>

Bob Wilson

 

I can see quite a bit of difference if my tire pressures are low. I'm sure that's been checked, but you might also want to see if they're the same on both. Hey, get froggy and swap tires while you're there...