Daox's 2004 Toyota Prius Build Thread - Page 7 - Fuel Economy, Hypermiling, EcoModding News and Forum

Matt Herring · 08-03-2009, 08:46 AM

Daox,

Just checked your fuel log to see how you were doing...are you using fill stats to report your mpg or working off MFD? I would highly recommend using MFD minus 2% to calculate your fuel logs as actual fill numbers are up and down and inconsistent.

Have you had any luck with using GPS lately?

Daox · 08-03-2009, 09:07 AM

I am using actual fill numbers. I understand it'll vary quite a bit, but it should all average out in time. I don't like the idea of using the MFD for tracking as it is not 100% accurate. When possible, I'm logging what the MFD said in the notes section. There were a couple fills when I wasn't tracking that, but I told my wife (who almost always fills it up) to start logging it.

I really haven't been driving the car a lot though. I only drove it one day last week. So, I haven't got to play with GPS too much. I did have a good commute in this morning according to the scangauge. However, its still not calibrated, so I can't say for sure what kind of mileage I'm getting. I just know that it is better than what I was getting before.

Matt Herring · 08-03-2009, 09:19 AM

Over my first 12 tanks I'm almost dead on (MFD is less than 1% optimistic so far) with fill vs. MFD but the guys over at priuschat all use the MFD -2% to monitor their tanks (they calculated that margin for error over hundreds of tanks of their own).

The SGII will never be calibrated for you due to the wide swings in fills. My current SGII setup is reading about 8 mpg pessimistic vs. my MFD and has been as much as 10 mpg optimistic as well. Your fuel log should eventually even out to close to accurate mpg after many tanks but it's difficult for you to guage success tank to tank by using the fills to chart your tanks. I know you are aware of all this but just wanted to let you know what I was doing to guage tank to tank success/failure.

Why don't you think the MFD is accurate? The more veteran Prius drivers report the MFD is about 2% optimistic over hundreds of tanks.

bwilson4web · 08-03-2009, 01:13 PM

Quote:

Originally Posted by Matt Herring

Over my first 12 tanks I'm almost dead on (MFD is less than 1% optimistic so far) with fill vs. MFD but the guys over at priuschat all use the MFD -2% to monitor their tanks (they calculated that margin for error over hundreds of tanks of their own). . . .

Not all. I use calibrated trip meter and fuel receipts and always have. I calibrate the trip meter by both mile markers and GPS. I've always considered the MFD to be an estimate that is useful for short range studies.

BTW, I have to calibrate the trip meter because of different, aftermarket tires. This can also lead to over-optimistic MFD mileage reports. Some of us have speculated about getting four, donut spares and driving to various 'driving contests.' But that would be wrong ... funny but wrong.

Bob Wilson

Daox · 08-03-2009, 01:35 PM

Like Bob said, its still just a best guess. There is no way for the computer to know exactly how much fuel you use.

I agree, a one tank SG calibration will not be enough. It will get it closer than it is now though. According to it, I got 81 mpg in this morning (and I know I wasn't close to that high). After the first calibration I'll probably calibrate after another 2-3 tanks. That should get it close enough for me. It doesn't need to be dead on IMO. Even now, as I got 81 mpg this morning, I can at least compare it to my drive home to see if its worse or better. I know that 81 mpg is good for me as I averaged in the 70s other times I've driven in.

Matt Herring · 08-03-2009, 01:40 PM

Got ya...an exact and inexact science at best in the Gen II Prius for sure. I'm going to stick with the MFD minus 2% as it is what I started with in my fuel logs. I do have fill numbers on my logs as well and I chart them both on a separate excel spreadsheet to have all the bases covered. Like I said before, ironically my fill and MFD numbers are very close after 12 tanks...only time will tell if they are similar a year from now.

Matt Herring · 08-20-2009, 05:30 PM

Haven't heard anything out of the Doax Prius camp lately...what have you been up to with the buggy? Any new mods or driving techniques you've been trying?

Daox · 08-20-2009, 10:08 PM

Oh, not too much going on with the car. I'm just settling into it a bit more and trying to figure out all the quirks. I'm also trying to train the wife how to drive it a bit better. I've mainly been using super highway mode to and from work on the highway. With it, I've been slowly upping the mileage. I seem to be pretty consistently getting low 60s on the way to work. On the way home traffic is a lot heavier. Sometimes this means I can really crank out the mileage, but most of the time I can only hit high 50s on the way home.

I will be going to the Milwaukee hybrid group meet this weekend and picking up a block heater and service manual. So, it'll have a block heater soon enough. The service manual will help out with another mod I want to do too.

And, I'd really like to at least get a partial grill block done sometime soon. We'll see how things pan out though.

Daox · 08-20-2009, 10:12 PM

I should also add that I think that a few good aero tweaks will really help out with SHM travel since you have a limited amount of power to assist your glide.

bennelson · 08-20-2009, 10:57 PM

I overtly snuck over to Daox's house tonight under the guise of seeing his house and having dinner.

But secretly, I was spying on the new Prius.

I did notice that the car was in the driveway, while non-operative vehicles occupied the garage.

I also saw the Prius used this last weekend to haul recycled windows. I'm sure the weight dragged down the fuel average, but it's a long-term energy gain when those windows get re-used for renewable energy projects.