2010 "Miles to Empty" Accuracy

I drove until the estimated miles til empty was 30 miles and then filled it and it took 9.45 gallons. It was also on the last pip. I'd worry about draining it too low. Plus it can be a long walk if it runs out on the highway.

 

The advantage with running the tank really low contrary to the instructions in the owners handbook which would, like every other car on the road advise that you keep at least 1/4 of a tank in the car, is?

 

Why?

Isn't 500 miles per tank enough?
.

 

General accuracy. I just filled up with 505 miles on my first tank. Pips were blinking and miles to empty said about 15 miles and I had a 30 mile trip ahead at night. If I knew I could have gone more I would have pushed to my favorite fueling spot.

The tank took 9.592 to auto-shut off yielding 52.64 MPG. I was a bit disappointed as total miles on Trip A indicator said I was averaging 55.6, and Trip B (a 200 mile trip) said 60.7. That's about a 5.3% error which is within tolerance I suppose, for the total tank.

I'm glad I potentially had another 121.5 miles till dry, but I would rather have accurate gauges than a dumbed down version for inattentive drivers. Next time, I plan to wait til any further warnings come on to see where they trigger. Of course, I will keep in mind the 5% error and the capacity vs estimates to keep myself from walking home

Lee

 

A newbie question: Is there another low fuel light, besides the last pip on the fuel gauge blinking (and the miles to empty approaching zero)? I've filled my new 2010 twice now; the first time I did not go down to the blinking pip (I still had 2) and only needed about 9 gallons, so I decided to try lower the next time and ran down to the blinking pip and miles to empty near zero, and that fillup was still only about 9.45 gallons. I guess there's no more low fuel warnings below this?

 

Bob Wilson tested this for us. The next warning comes too late, after the car is already out of gas and the battery is exhausted. At least the Gen2 gave a warning before the battery was empty, giving a little time to find a safe parking spot. Gen3 does not.

There is an additional warning, DTE = 0, but only if you look for it. This will typically be about 25 miles after the blinking pip. For most cars this is long before truly empty, but one driver went dry just 7 miles after noticing DTE = 0. We don't know how far he went before noticing.

 

Well there's several myths and urban legends, they go like this

1) There's crud and dirt in your tank. As long as there's enough fuel, a lot of that crud and dirt doesn't get sucked into the fuel line because the flow of fuel is relatively low. Once fuel gets ultra low, the likelihood of that crud getting pumped is increased.

2) As fuel is consumed, regular air goes into the tank to replace the fuel that was there. At night, or in colder weather, the water vapor in the air condenses and goes into the fuel. As long as there's enough fuel, the water at the bottom of the tank is diluted as the fuel is pumped and no major harm is done. When fuel gets low, the ratio of water can be higher and that is what gets pumped.

I guess this may not exist in Gen II with the bladder.

3) The fuel pump is cooled by the fluid it pumps. Running out of gas will cause the fuel pump to go burn out, ending with a several hundred dollar repair.


Finally one thing that may or may not be the case:

Fuel pumps usually pump constant amounts of fuel to the engine and then the fuel that is not used is returned to the tank. During this trip by the hot engine, the fuel heats up. The return of fuel to the tank recombines it with cold fuel and prevents it from boiling. If you have very little fuel in the tank the gas will heat up and potentially reach the gasoline's boiling point.

 

I've never bought that argument. The fuel is pulled from the bottom of the tank no matter how much gas is in it.

 

Thanks. This is as I guessed, that it's leaving a reserve (I was watching DTE also) but I thought I'd ask to be sure. I thought I'd be able to use closer to the 11.9 gallon tank capacity, having to fill up around 9 or 9.5 gallons makes 500 mile tanks not as easy as I expected. It seems like it's leaving 20% of the tank capacity as a reserve (unless maybe I'm not getting the tank full when I fill up; I didn't try to keep filling after the pump shut off). I don't think I want to go too far beyond empty, because then I'm blind as to how much reserve I really have left.

 

When the pump shuts off I can get 1-1.5 gallons more into the tank.

 

Depends on the actual pump and probably other factors. Some are more sensitive than others.

 

I can trickle about 2 gallons into the tank of my Gen III V after the pump stops for the first time. Are there any problems with this top-off practice?

 

Some have noted that it could damage the evaporative emissions system by flooding it. Personally, I just fill up until it stops once; I can get 500 miles from there, what's an extra 50 or 100 really worth?

 

Me, too. It shuts off and I have an est range of around 500 miles. However, if I drive those miles I understand that when the 0 mile range blinking begins there's still another 1-2 gallons. Thus I think that when it shuts off it must honestly be pretty close to full. No idea how people are squeezing 1-2 more gallon in when it's presumably already full.

 

I always top off and always get right about 2 gallons in after the auto shut off. Bob Wilson's "run it out of gas on purpose" tests showed there is about 2.1 gallons left when the last bar starts blinking. I don't know how much of that 2.1 is usable though. I think the furthest I've pushed it is around 30 miles beyond DTE=0. I have pumped just a bit past 12 gallons several times, including topping off.

 

Many fuel tank designs pickup fuel above the bottom of the tank, leaving an area for crud to safely accumulate. This is standard practice for boats and aircraft. I can't say whether the new Prius tank is built this way.

Tom