10x MPG doesn't work for me

camner · 12-22-2007, 09:57 PM

I've read a number of posts suggesting that a good way to determine when it's time to fill up is when one has gone about 10x the MPG reported on the MFD (assuming one got a complete fill up the last time).

I've only gone about 3000 miles in my 2007 Prius, but my last pip has always started flashing well before 10x reported MPG (minimum of 50mi before, usually about 70-100 miles before). Calculated (manually) MPG is always less than MFD reported mpg also.

Any chance I've got a bum mpg calculator, or am I missing something obvious here?

**efusco** · 12-22-2007, 10:02 PM

John1701a and others have suggested 9x the mfd number is a safer choice. I don't use any multiplier...I fill when I have 1 pip or when the last one starts flashing no matter what my mpg/distance on tank. The gas tank is so variable both in when the pump shuts off and the capacity of the tank depending upon temp that any preset number seem fraught with error.

qbee42 · 12-22-2007, 10:08 PM

In addition to the error inherent in the fuel capacity figure, doing a x9 or x10 calculation assumes your current mileage is the same as the average mileage, which may or may not be a good assumption. Driving down the highway with steady weather it might be okay, but day to day with temperature changes and snow on the road, it's anyone's guess what your current mileage might be. I do what Evan does, and fill up when the gauge tells me too.

Tom

F8L · 12-22-2007, 10:09 PM

I'm with Evan. I fill up when I reach 2 pips to be safe. None of my other vehicles got more than 380-400 on a tank so it doesn't bother me to fill that frequently.

john1701a · 12-22-2007, 10:16 PM

Quote:

Originally Posted by efusco

John1701a and others have suggested 9x the mfd number is a safer choice.

A safer choice to help you determine a personal distance limit.

For me, that worked out to filling up by 350 miles in the winter and 450 miles in the summer.

.

Neicy · 12-22-2007, 11:11 PM

Quote:

Originally Posted by camner

Calculated (manually) MPG is always less than MFD reported mpg also.

Any chance I've got a bum mpg calculator, or am I missing something obvious here?

If you are topping off your tank, the calculated mpg will be less than the MFD mpg. If you average at least 5 tanks, they will be very close as long as you are NOT topping off your tank.

If I waited until 9X my mpg on this tank (which finally got down to 2 pips so I could get rid of it) I would have run out of gas because of the gas used to de-ice and de-fog my car so much lately with all the storms. This time of year the bladder is reluctant to stretch as much due to the cold making it stiff. Even though I was down to 2 PIPS it still only took 6.97 gallons. You will see a difference when the summer comes and also as the car ages.

Stev0 · 12-23-2007, 01:56 AM

I'm another down-to-one-pip guy. And by that, I mean I fill up ASAP the minute I see one pip (some of the more daring folk here wait until it's flashing. They're nuts).

**Tideland Prius** · 12-23-2007, 02:14 AM

Quote:

Originally Posted by Stev0

I'm another down-to-one-pip guy. And by that, I mean I fill up ASAP the minute I see one pip (some of the more daring folk here wait until it's flashing. They're nuts).

I don't think so. The blinking pip just means it's low on fuel. It's no different from the Low Fuel light coming on in regular cars. In fact the blinking pip is essentially the substitute for the Low Fuel light.

patsparks · 12-23-2007, 06:50 AM

People call it a guess gauge but it is better than all the calculating. Start looking for fuel at 2 bars on the gauge, fill urgent at 1 bar, you have waited too long if the last bar is flashing, fill very urgent.

Once you have 1 bar on the gauge you don't know how much fuel is in the tank. I really don't follow the reasoning in stretching a tank to the limit, it won't reduce your overall consumption. If you get about 450 miles from a fill-up rather than stretching to 500 miles you will need to fill up one extra time each 10 tanks or 4500 miles, is that too big a price for knowing you won't run out of fuel and be stranded on a cold dark night on the rough side of town? It also means you won't be trying to drive on the traction battery alone trying to get to a petrol station which must be bad for the very expensive battery. I wonder if the HSD computer stores a code if the car is driven while out of fuel? Could that affect warranty?

Spinnerbug · 12-23-2007, 07:44 AM

I have read alot of mention of the Bladder in the fuel tank. Can someone either direct me to a post where this is explained a bit more in detail or explain what the Prius uses regarding the Bladder in the fuel tank. All of my previous cars have had a solid fixed volume tank...Unless I am thinking of the Bladder concept in a wrong way, I am a bit confused.

12-22-2007, 09:57 PM	#1
camner Junior Member Join Date: Sep 2007 Posts: 19 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	10x MPG doesn't work for me I've read a number of posts suggesting that a good way to determine when it's time to fill up is when one has gone about 10x the MPG reported on the MFD (assuming one got a complete fill up the last time). I've only gone about 3000 miles in my 2007 Prius, but my last pip has always started flashing well before 10x reported MPG (minimum of 50mi before, usually about 70-100 miles before). Calculated (manually) MPG is always less than MFD reported mpg also. Any chance I've got a bum mpg calculator, or am I missing something obvious here?

12-22-2007, 10:02 PM	#2
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 14,225 My Car: 2004 Prius Package: #9 Nominated 1 Time in 1 Post TOTM Awards: 0 Friends: 24	Re: 10x MPG doesn't work for me John1701a and others have suggested 9x the mfd number is a safer choice. I don't use any multiplier...I fill when I have 1 pip or when the last one starts flashing no matter what my mpg/distance on tank. The gas tank is so variable both in when the pump shuts off and the capacity of the tank depending upon temp that any preset number seem fraught with error.

12-22-2007, 10:08 PM	#3
qbee42 Senior Member Join Date: Mar 2006 Location: Northern Michigan Posts: 5,639 My Car: 2006 Prius Package: #7 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 6	Re: 10x MPG doesn't work for me In addition to the error inherent in the fuel capacity figure, doing a x9 or x10 calculation assumes your current mileage is the same as the average mileage, which may or may not be a good assumption. Driving down the highway with steady weather it might be okay, but day to day with temperature changes and snow on the road, it's anyone's guess what your current mileage might be. I do what Evan does, and fill up when the gauge tells me too. Tom

12-22-2007, 10:09 PM	#4
F8L Collecting Data on Nature Join Date: Aug 2006 Location: Sacramento, CA. Posts: 3,989 My Car: 2005 Prius Package: #4 Nominated 1 Time in 1 Post TOTM Awards: 0 Friends: 15	Re: 10x MPG doesn't work for me I'm with Evan. I fill up when I reach 2 pips to be safe. None of my other vehicles got more than 380-400 on a tank so it doesn't bother me to fill that frequently.

12-23-2007, 01:56 AM	#7
Stev0 Aluminum Member Join Date: Sep 2006 Location: Northampton, MA Posts: 4,711 My Car: 2006 Prius Package: #7 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 7	Re: 10x MPG doesn't work for me I'm another down-to-one-pip guy. And by that, I mean I fill up ASAP the minute I see one pip (some of the more daring folk here wait until it's flashing. They're nuts).

12-23-2007, 06:50 AM	#9
patsparks Uneducated bird-brain Aussie Join Date: Jul 2007 Location: Adelaide South Australia Posts: 4,905 My Car: 2004 Prius Package: Base Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 17	Re: 10x MPG doesn't work for me People call it a guess gauge but it is better than all the calculating. Start looking for fuel at 2 bars on the gauge, fill urgent at 1 bar, you have waited too long if the last bar is flashing, fill very urgent. Once you have 1 bar on the gauge you don't know how much fuel is in the tank. I really don't follow the reasoning in stretching a tank to the limit, it won't reduce your overall consumption. If you get about 450 miles from a fill-up rather than stretching to 500 miles you will need to fill up one extra time each 10 tanks or 4500 miles, is that too big a price for knowing you won't run out of fuel and be stranded on a cold dark night on the rough side of town? It also means you won't be trying to drive on the traction battery alone trying to get to a petrol station which must be bad for the very expensive battery. I wonder if the HSD computer stores a code if the car is driven while out of fuel? Could that affect warranty? __________________ All the warranty I need. And for thrills -> Still averaging 4.4L/100km across town 2004 silver base model Prius Shark fin, genuine mudflaps, colour matched side mouldings, rear bumper scuff guard, sheepskin seats, BT Plate. I love it!

12-23-2007, 07:44 AM	#10
Spinnerbug Junior Member Join Date: Nov 2007 Location: Lincoln University, PA Posts: 21 My Car: 2008 Prius Package: #6 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Re: 10x MPG doesn't work for me I have read alot of mention of the Bladder in the fuel tank. Can someone either direct me to a post where this is explained a bit more in detail or explain what the Prius uses regarding the Bladder in the fuel tank. All of my previous cars have had a solid fixed volume tank...Unless I am thinking of the Bladder concept in a wrong way, I am a bit confused.