Why an 8 to 10 mpg difference between our 2006 & 2008 Prius?

But the 2005 and 2012 are different generations with different engines and different batterys. Tire sizes are different, the aerodynamics are different. I would expect Toyota to have done better on the 2012, and they did.

 

You are exactly right. I just wanted to point out that a 2012 in my normal daily suburban use situation does get several mpg better fuel mileage than the 2005 model. John

 

Gen3 among other improvements warms up faster so less MPG loss in first 5-10 mins (I heard)
but OP has two Gen2's.
OP one cause could be steering alignment also.

 

Have you tried swapping the 12v batteries between the cars?

 

Thanks for taking the time to test it thoroughly and keeping us updated.

Difference in engine efficiency (due to engine cleanliness and injector condition etc) could also cause an mpg difference. Your observations of the engine running more often and the SOC being generally lower for the 2006 however do seem to point to difference in the HV traction system.

F8L's idea of swapping the 12V batteries is a good one. I would be good to rule out that as a possible source.

 

The Michelen fuel saver A/S gets better mileage than the Michelen fuel saver regualar which gets better milage than the goodyear intergity. Just the differnce between the two tires is worth quite a chunk in MPG.

Further how accurate is your tire pressure between the two cars? You have to have the cars parked for several hours without a heat source affecting them differently (avoid some tires sitting in the direct sun and some in shade). Use an accurate tire gague.

Between the difference in tires and a few PSI it could explain the entire difference.

 

Yes but it's the other way around. He has the Michelen fuel saver tires on the 2006 Prius which is experiencing the lower MPG.

 

It's Michelin Energy Saver A/S or Goodyear Assurance Fuel Max. You're mixing the two together. Both are more fuel efficient than the Integrity.

 

Honestly with Priuschat's new wall of text style I didn't read all of his posts.

A few

returns

for more white space would make his posts much more readable.

Though looking at my post I see the new message editor on priuschat makes formatting the message a much more cumbersome prospect than it did in the past. I literally edited this message 7 times to get something close to the white space I was trying for

It seems to remove hard returns if you don't spend a lot of work putting them back in.

If the better tires are on the car with the worse MPG then it is a mystery of an even larger proportion.

 

Yes I was quoting the OP verbatim on that, I thought Michelin might have had a different name for them in the US. TeamPace can you clarify exactly what tires you have?

If you're sure that it's differences in the traction battery that's causing it, then what I'd is to try to find a nice quiet stretch of road that's pretty flat and measure the distance it can travel at low speed (say 25MPH) before the engine kicks in.

What about this for a test procedure (assuming you can find a suitable stretch of road and time of day that you can go 25 MPH)

0. Check tire pressures and oil levels to make sure everything is the same. Then one at a time test each car with all AC heat and other accessories off.

1. Take the car for a drive and get it well warmed up then let it idle to stage 4. Check that it's in stage 4 and the engine cuts out at low speed glides. Try to complete this with 6 bars SOC.

2. Stop near the beginning of your flat test road and force charge it until the 7th (green) SOC bar first comes up, then stop charging immediately.

3. Use the ICE to accelerate up to 25 MPH and then backoff and let it go into full electric mode.

4. Keeping very gentle and steady accelerator pressure, just enough to maintain 25 MPH. Record how far it travels before the ICE cuts in and how many bars of SOC are showing when this happens. Report the differences of the two cars.

This result could be very interesting. Don't forget to have all heat and accessories off when you do the actual glide part. BTW if you didn't know, to force charge you just leave it in "D" and with your foot firmly applying the break you gently rev the engine at the same time. You'll see the arrows showing the battery charging when you do this, and assuming that you're starting 6 bars, then the 7th bar should come up in just a minute or two.

 

...I don't trust the MFD's...sometimes my 2006 MFD is reading steady 50-51 MPG then I stop for gas and then I am down in the 45-46 range. I don't think in reality my MPG is changing it's just the display...usually turns out the lower value is more realistic with the fill-up data calc.