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?
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.
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
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.
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. .
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.
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.
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?
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.
Think of a rubber bag filled with gas. The bladder expands and contracts as fuel is added and used. It keeps the gas from contacting free air, and as a consequence, reduces the amount or evaporation. Tom
Here is a link to a PDF link in Efusco's post that will help you. http://priuschat.com/forums/showthread.php?t=38572&highlight=fuel+tank+bladder
So many folks wait until they get down to the last pip or two on their gas gauge and I wonder is it just to see how many miles they squeeze out on a tank? It doesn't seem that waiting so long to fuel would change the mpg any. Since the tank is a bladder and it being winter, wouldn't it be better to keep that bladder closer to full versus empty? I'm just curious about what other opinions are. Speaking for myself I've always am wanting to fill up when my cars have reached the half way mark...just sort of a comfort zone - no real logic.
I agree, ehat is hte diference if you fill up at the mid pip or the last one? if you track the mpg and gals per fill ups, they will all balance out. I know in a reg car it is not good to let the tank get below 1/4 full. many mechanics have told me this due to moister buildup that may occur over the years. the manual state that the tank will decrease in the amount it will hold a max of 1.3(i think) gal when the temp reaches like 20 deg F. its not like you are only going to only get 4-5 gal inthe bladder on a cold day. Again, it will average out over time.
Try It and See I think you should try it and see if the 10X works. If you run out of fuel then you will have solved the mystery. Also, try refilling a box of wine bag to the same level it was when you purchased it. While I agree that the anal control freak in me will be forever frustrated by the lack of accuracy with the fuel economy of this car, the fact that I pay 1/2 as much, 1/2 the time and go twice as far usually overcomes any contempt I had developed earlier in the purchase. However, if you're still unhappy, just put a gallon can in the back of the car and drive it as far as possible. I intend to do it when the weather turns 'warm' here in the South.
Thanks all for their replies. I'm not anal about squeezing the last possible ounce (or ml) out of a tank of gas. With all my cars, I always let it go pretty low (but have never run out of gas!). The station I like to use is not on my usual path (there are no good stations on that path), so I like to wait until I go by it natually, if possible. With each new car I always try to mentally "calibrate" the gas gauge so I know when I really need to fill up. For example, with my recently retired (kids now gone) Dodge Caravan (wow...what a difference in MPG!), I could go about a week after the low fuel light lit up and about 2 days after the gauge itself was pinned on empty. I'm just trying to figure out the analog for the Prius so I don't go dry.
I refill no later than when there is one pip left on the guess gauge. Never ran out of gas, never will. Some people also say you should never drive so the gas milage display on the MFD is less than half your speed. Another stupid piece of advice. If I tried to do that I wouldn't make it up half the hills around here. Sometimes people just have dumb ideas. That's life.
If you guys are really concerned about total mpg, don't fill up all the way. Driving around with half a tank or less means you are dragging around less weight (5+ gal @ 6 lb/gal) and getting better mileage. The difference may be hard (impossible) to measure but it does exist. I fill up when it is convenient and/or a good price. Never let it get below about ¼ tank.
