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New Yorker 11-21-2007 11:31 AM

MPG manual calculation a must!
Toyota Prius computer exagerate MPG

I love my Prius. But:

Every tank I gas up, my MPG manual calculation from tank to tank is 5 MPG lower than Prius built-in computer display.

Green Hybrid web master should mandate all users to use manual caculation. As a group, we can see which model has an acurate MPG according to its computer display. :cry:

This is a separate issue than all hybrid cars re-evalueated every manufacturer's EPA, starting from 2008 models. :confused: Thank god they became more realistic.

Qslugs 11-21-2007 12:46 PM

Re: MPG manual calculation a must!
Yep, the Camry in my opinion is about 1-1.5 mpg off as well. I usually add my numbers up manually - take millage and divide it by gallons of gas in car at time of fill up. I think thats how most of the people around here do it actually. I have a stack of receipts dating back to my cars purchase.

wdmark 11-21-2007 01:12 PM

Re: MPG manual calculation a must!
Ironically I just added another tank to the database on my TCH. For all my entries to date I've used the MPG off the TCH display. I usually refill at about 1/4 tank but today was a top off for holiday travel. Miles traveled 127 and MPG per display of 40.6 I was happy as this was above average for me and after trying some new things (i.e. no AC here in FL & 40PSI Tire pressure. But, as posted in my cryptic notes for this tank in the database:

"First Partial Tank with no AC use & after increasing Tire Pressure to aprox 40 PSI. I enter MPG from TCH display and this was much higher BUT purchased 3.495 Gallons for 127 Miles which is actually 36.337 MPG?"

Seems like a material difference to me. BTW purchased fuel where I almost always do and I always allow the pump automatic shutoff to do its thing. I have records of each tank that would allow me to go back and sample or calculate manually...and I just might....but for now I've got to burn some unknown amount of fuel. Happy Thanksgiving to all.

Mr. Kite 11-21-2007 03:00 PM

Re: MPG manual calculation a must!
You better use GPS to calculate miles driven while you're at it. Those odometers can be quite a bit off.

phoebeisis 11-21-2007 04:02 PM

Re: MPG manual calculation a must!
Hey,same here.My running total on the Prius display is always 3-5 gallons more optimistic than actual.It usually reads 45-46 for the tank, but actual calculations say 41-43.

n8kwx 11-21-2007 07:50 PM

Re: MPG manual calculation a must!
A caution on using tank averages on the Prius. From what I have heard, the fuel tank bladder can make the capacity of the tank vary from tank to tank.

Best way is probably to do a tank average average (many tanks) to derive an offset to the indicated MPG. Once you know the offset, use the indicated display and offset it.

New Yorker 11-21-2007 07:58 PM

Re: MPG manual calculation a must!
My Prius computer displays CONSISTENTLY 5 MPG more than the actual, every tank!

I bet there is not a single car, any make, displays lower MPG than manual.

kenny 11-21-2007 10:31 PM

Re: MPG manual calculation a must!
I have about 36 tanks now.
For the first 20 or so I religiously compared the dash to the pump.
The dash averaged 1.4 MPG lower than the pump.

I have always entered my miles driven and gallons pumped and let the database calculate the MPG.

Funny, in my first generation Civic Hybrid, 2004, it was a couple MPG the other way.

gumby 11-22-2007 12:25 AM

Re: MPG manual calculation a must!

Originally Posted by New Yorker (Post 150862)
I bet there is not a single car, any make, displays lower MPG than manual.

Not true! It appears that the Honda Civic Hybrid 2006-up generally displays a little less MPG than actually calculating it. My car certainly does (usually). I keep notes for each fill-up in the GreenHybrid Database of displayed MPG, Actual (calculated) MPG and price paid. Check it out.

Regardless, I think calculating it is the only (close to) accurate method.

300TTto545 11-22-2007 01:51 AM

Re: MPG manual calculation a must!
+1 for my 2007 Civic. It is about 1-2 mpg lower than calculated. Every once in a while, it is the same and I am dissappointed. I had a 58.8 computer reading and I thought for sure I would get 60 on manual calculation - but it came in within .1 of the computer.

I do think that most cars come in more optomistic than the screen.

I am not a database person but I would have thought that manual calculations are mandatory. If people are entering it based on the computer estimate, it sounds as if the HCH-II would be a bit better in the real world than the Prius.

My lifetime is about 52.5 computer and almost 54 calculated. 11k miles.

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