Efficient driving for a 1,000 mile tank

July 12, 2013


Back to my regular, marathon driving schedule. This is the morning commute including only 30 minutes of 'running laps.' I also have a photo of the tank which is now showing 5 bars.

Given I've burned about 4.76 gallons, the tank level is consistent with an assumed capacity of a little over 10 gallons . . . indicated to the driver. In fact, our tank has measured 12.1 gallons so we're looking at a projected: 1,093.8 miles

Sometime this weekend I should pass the 500 mile mark needed for the 'high mileage' list. I'll add a posting to this thread but won't 'officially' offer it to the 'high mileage' list. My plan is to complete this marathon tank and 'book it.'

BTW, I have walked away from a number of enhancements . . . things that could have used increased this tank mileage:

• Added more 'laps' on the 99.9 MPG loop - right now, my 'laps' to 'trip' ratio is running 50/50. I could run more laps for each trip and make the ratio closer to 66/33 or even 75/25 for a higher MPG number. I would expect to see values close to ~95 MPG. If I just dedicated the car to 'laps', I could achieve 99.9 MPG
• Quantified fuel energy - running 'generic' Costco, E10 may not have the energy content of a local Fuel City station that sell straight gas that is more expensive but may have a higher energy content. Understand that measuring gasoline energy content is not trivial but could add several percent increase in MPG.
• Aero mods - bumper inlet and wheel well covers.
• Over-drive tires - replacing the front tires with over sized, larger diameter tires, in effect gives a proportional improvement in real MPG. With our NHW11, I'm seeing a solid, 5-6% increase in MPG due to lower transmission and tire rolling drag. However, it would require GPS and mile marker calibration factors and would not show up in the display.
  • Cheater tires - using tiny tires and neglecting to share the calibration constants. In effect, driving a true 900 miles but the display showing 1,000 miles. This also rates up there with suspending the car and spoofing the speed sensors to 'dial in' whatever numbers one wants to see. One might as well just buy a salvage display, put it on a bench with a power supply and interfaces and electronically drive it to the max: 99.9 MPG, average speed 100 mph, full tank, and no errors . . . or just Photoshop it.

Regardless, this experiment is ~40% done after five days or about 8% per day. We have about eight days remaining.

Bob Wilson

 

Remember this is just an experiment based upon a marathon driving technique pioneered by our good Prius friends in Japan:

BTW, I think the top of the list is 99.9 MPG with just over 500 miles, a Prius c. The second one on the list is pretty good too just under 900 miles. I see turning in 1,000 miles at 90 MPG will put me in good company. But I also wanted to show how it is done in terms that anyone can follow:

The real success is not this particular tank. The real success is seeing others adopt and tailor the elements of this marathon to explode the number of "1,000 mile tank" club members. So like the people who live in Lake Woebegone WI,"all the children are above average."

I am deadly serious when I say marathon driving is NOT anything I would wish on anybody else or in traffic not of your choosing. . . RUSH HOUR NO! Some elements are useful BUT you're not going to suddenly be turning in consistently higher tank numbers. But as you see the tricks, you can reduce the number of abysmally poor tanks . . . and not be the "horse's nice person Prius driver."

Bob Wilson

 

July 13, 2013


About 5.57 gallons used of an expected 12.1 gallons in the tank, about 46% of the way done.

My usual, daily commute is 20 miles per day. During the marathon, I'm running about 80 miles per day.

Bob Wilson

 

July 15, 2013


Now 7.09 gallons burned, 58% done.

Bob Wilson

 

July 16, 2013


Exactly 66.66% to the miles goal after using 61% of the tank. So far, 7.37 gallons burned out of 12.1 gallons.

Bob Wilson

 

July 17, 2013


The fuel tank indicator is on the last pip but not yet in flash. So we're at 75.8% of the mileage goal and at 8.35 gallons, 69% of the fuel burned. If the car reaches 820 miles before flash, it will be a piece of cake to reach the goal. Every thing looks good for completing the marathon drive this weekend.

Sad to say, I'm in flash at about 775 miles, about 45 miles short of what I was hoping to see. There is always that "flash" has offset from the 2.1 gallons measured four years ago. Still, I'll put the spare can in the car and switch to energy flow.

This is what I saw when I parked at home this evening:

The mileage is 80.4% there and the calculated fuel burn, 8.84 gallons, 73% of the expected 12.1 gallons.

Another hypothesis is the relatively low fuel burn may have moved into a non-linear, area. However, I didn't "burp" the tank so it is possible I didn't get a full 12.1 gallons. Guess I'll just have to continue until it runs out.

Bob Wilson

 

I'm running roughly 50/50:

• 10 mile commute in the morning - 10 mile loop
• lunch - loops for an hour (makes up for other errands)
• 10 mile loop - 10 mile commute home
• errands - often too far from loop to do laps

Not really. This is terribly boring and the only salvation is breaking it up across the two weeks. Once the 'bowling trophy' is on the wall, I'm going back to my real life.

In the summer, I typically get 55-60 MPG in the daily commute. In the fall and spring, typically 50-55 MPG. When freezing, it is 48-50 MPG.

Bob Wilson

 

Taking a break due to forecasted rain. I'll pick it up again Friday and finish this weekend.

Bob Wilson

 

Sorry, no pictures but just a quick status:

• "A" tripmeter
  • ~850 miles, ~91 MPG, ~22 mph
  • ~9.34 gallons burned out of 12.1 gallons expected
  • ~251.1 miles remaining
• "B" tripmeter
  • reset on "flash" at ~975 miles
  • ~75 miles, 99.9 MPG, ~22 mph
  • ~0.75 gallons burned out of 2.1 gallons expected
  • ~134.8 miles remaining

Unfortunately "B" tripmeter is pegged at 99.9 MPG so I can not use it to more accurately gauge when the last of the gas is burned. For now, the "A" tripmeter remains my best estimate and it projects close to 1,100 miles on this tank . . . assuming I filled it correctly. I failed to "burp the tank" so we won't know until the end.

I've switched to the "energy flow" display since having the power arrows go away is the only way to know the gas is finally gone. This has given me new insights to how to do a marathon drive. With some video captures, I should be able to write up a 'less involved' set of instructions.

With luck, I should complete the marathon drive this weekend.

Bob Wilson

 

July 20, 2013


According to this display, 9.86 gallons of 12.1 gallons, burned leaving 2.24 gallons, easily enough to reach 1,000 miles.


According to this display, 1.30 gallons of 2.1 gallons (after flash), leaving 0.80 gallons, not enough to reach 1,000 miles. However, we know 'flash' sometimes is triggered too soon by slopes and hard turns.

Regardless, we'll have an answer between now and Sunday.

Bob Wilson

 

July 21, 2013


Looks like I burned 10.9 gallons, not the 12.1 expected. I suspected I did not get a full-fill as I had to turn the nozzle upside down to reach the tank . . . wrong side fill.


There is still gas in the tank but I don't know how much. The experiment continues.

Bob Wilson

 

I did but not very far. I had pulled into work to check on some long running jobs which meant at a minimum, a catalytic converter warm-up. I planned that stop and pretty hit my mark.

After checking my jobs and leaving work, I got about a mile and a half down the road and had stop at a light, on a downgrade. When the light changed, I noticed my power flow arrows were gone, the signature of "dry tank." So I set my flashers and already at 25 mph, proceeded another half mile to a safe, shady place to add the spare gallon.

From there, I drove directly to Costco and added 11.1 gallons, $3.15/gal. So I'm sure the tank is 12.1 gallons . . . and I've added one more 'run it dry.'

I'll post the photos from the 'dry tank'', fill-up, and gas receipt later today. I'll also write up a simplified script, one that uses just the stock Prius displays to replicate how efficient driving can achieve a 1,000 mile tank.

Other than boring and a waste of time, achieving a 1,000 mile tank is no big deal. As far as I am concerned, whatever mileage you get over a 10 mile stretch, both ways, back-to-back, is perfect. Multiple the MPG times the tank capacity and 'have a happy.'

Bob Wilson

 

The Prius has been one of the first, non-electrical powered vehicles where the drag forces literally dictate the fuel consumption and economy. In contrast, ordinary gas and even diesel engines and transmissions have significant inefficiencies especially at low power settings which has taken a long time to figure out. One key is engine-off operation to avoid the inefficient, lowest power operating modes.

At idle, an ordinary engine, gas or diesel, has to burn fuel to overcome mechanical friction. The idle, fuel flow produces no excess energy and is the least efficient way to burn fuel. But our car in 'hybrid mode' will burn fuel at a high enough rate that the engine mechanical overhead disappears in the noise. The problem is this is a higher power level than the car drag demands.

The Prius trick is the transmission 'banks' the extra energy into the traction battery. Then as soon as it can, the engine is turned off and the stored energy is used to sustain velocity. I see this in my marathon experiment because it consists of long, boring hours on cruise control, away from traffic.

After the warm-up, I'm seeing:

• ~0.20 gal/hr - no load idle in "N", rarely seen during the marathon drive
• ~0.50-0.60 gal/hr - lowest fuel consumption during the marathon drive, ~30%
• ~1.2-1.5 gal/hr - highest fuel consumption, marathon route, "D", ~20%
• ~0.02 gal/hr - engine off (probably used to avoid divide by zero), ~50%

Bob Wilson