Gas Pip Lines

Gas gauges are almost never linear, and the ones in the Prius are no exception. At best, a gas gauge gives you some idea of how much gas is in the car: half tank, quarter tank, nearly full. Don't expect any finer information than that. Mostly the gauge tells you when it's time to fill up.

In most cars, the gas gauges are set to stay at the top for awhile, then get more accurate as you get near the bottom of the tank. It's more important to know when you are nearly empty than when you are nearly full.

Tom

 

I think Tom is right on. People expect that because the gauge in the Prius is digital and has 10 bars its somehow more accurate than others. That said, the gauge is usually pretty good. Its usually our mental calculation thats causing us to doubt it based on what we think it should be. The gauge does a pretty good job showing how much gas is left in the tank relative to how much you put in. Since the size of the tank varies due to the bladder, what it doesn't show is a fixed number of gallons or miles per pip.

Here's my strategy. I fill up as soon as the last pip blinks, I fill at half speed, and I never try to top up (unless it stops really early). This is usually around 8-9 gallons, though I've gotten close to 10 with the high summer temps here. Whatever I put in, I assume that is all the gas thats in the tank because its all I can be sure of. Whatever may be left in there I just consider a reserve that I'll hopefully never use. Then I usually just drive it until it blinks again and don't worry about it.

If I'm on a long trip and I'm worried about when to fill up I use the following estimate: Gallons added, divided by 11 = approx. gal per pip, times average mpg = approx miles per pip and then I err on the side of caution. So if I put in 8 gallons, and divide by 11 (I add one since it usually seems to take about 1 extra pip for the gauge to start going down) then I would expect to get about 0.73 gallons per pip. At 48mpg that would be about 35 miles per pip. I think a lot of people automatically think 10 gallons, 10 pips, 50mpg, equals 50 miles per pip which is where people get into trouble.

My advice? Don't worry about it. If you routinely fill up as soon as you drop to two pips, you should always have a buffer of 50-70 miles to find a gas station. If you are on a trip and may not see gas for that long, I'd just play it safe and fill up sooner. As nice as it is to get 450-500 miles out of a tank, its really not that big a deal to fill up after 300-350 like most folks do anyway. I always ride it down to just when the last pip flashes because I'm lazy, and I'm in the city and know I can always fill up with a mile or two. On long trips across the desert I'm much more conservative, as I would be in any car.

Rob

 

I agree pretty much with Rob. I track when the first (10th, if you prefer) pip disappears. That usually occurs at 180-220 odometer miles. And that rate seems to be based on the mpg I'm getting at the time. (I also recognize that I may not have filled the tank to the previous fill's point.) It seems to me that first pip disappears at 3-4 gallons. Each additional pip turns off at approximately the same point per gallon. Rob says .7 gallon or so; I use 35-40 mpg. Could be slightly more, depending on the current mpg's I'm getting during that pip's lifetime. I did the same thing with my F-250's analog gauge, and the principle seems to hold -- the needle won't come off the full mark for a while, then it drops at a consistent rate, so I know that when I'm at the half-full mark, the truck has used 8 gallons of its 17-gallon tank, but the next quarter-tank really only monitors the use of 2 gallons, because I know that at a quarter full I'll put in 10 gallons.

So I take the position that each Prius pip disappears at a rate consistent with the current gas usage. If you're slurping fuel at the first 4-5 gallons and are down 2 pips, then suddenly start driving more conservatively, the next few pips should disappear at a different rate.

That's my story and I'm sticking to it -- until someone smarter than I am has a better idea. Shouldn't take long.

 

The consensus is to fill at 2 pips, maybe 1 but immediately if the final pip starts flashing. How exciting do you want your gas station contacts to be? At best, mayb e you should fill when you feel uncomfortable about running out of fuel.

Seriously, the disappearing of pips is based in part on how much gas you put in the tank. If you pump in at full speed, you probably will have less fuel than if you dribble it in, because vapors fill some of the space. That, in turn, will affect how quickly the first pip disappears. Another factor in low mpg initially could be the newness of your car. It takes ssveral thousand miles to break in, they tell me.

You are right on this: Prius does take some time to adjust to. Most feel it's worth it.

 

Re: Help on Battery

Okay, lean in here a little closer. A little more... :fish:

You've just been smacked with a trout. That's for asking the #2 most common PriusChat question without doing a little reading before you asked.

Here is the short answer: the Prius tries to keep its battery charged to the middle blue zone. This gives it power when it needs it, but still room to collect power during regenerative braking. It's not normal for the battery to charge all the way to the green zone. It will happen under special circumstances, but the controller will soon draw it back down into the blue zone.

You don't have to worry about the battery; it takes care of itself.

Tom

 

Now Tom, be nice.

From what others have said, it seems to take a while before you see 7 green bars more than once in a while. As the car breaks in you will probably see them more often. That's what I experienced too.

 

I wonder why they made the target zone blue instead of green? Green typically means good, go, etc. So the target charge zone would be the natural choice for this color, not blue. If they had made high charge blue I wonder if the driver (including me) would be less inclined to initially question why they weren't getting into the upper zone?

<dodges trout>

What puzzles me is why it will charge into the green zone easily at times and then be obstinate about wanting to run the ICE in a low efficiency zone (lugging) when I would prefer to burn off the excess charge before the next hill/stop. (Very hilly city driving.)

 

Nice dodge. You must be faster than I though.

As for green, it's not a good thing to have your battery charged to green. Green means that something is forcing the system to work outside of its target settings. It doesn't mean that there is a problem, it just means that special conditions have forced the battery outside of target.

What can cause a green battery? Several things:

1) Descending a long hill. The regenerative braking makes electricity, which has to go somewhere. It's used to charge the battery. A long hill will charge the battery to green. Once the battery reaches the high limit, the Prius will no longer use regenerative braking.

2) Engine running to make heat. You will get a green battery more often in cold weather. This is because the Prius needs to run the engine to make heat, both for the engine itself and for heating the cabin. While the engine is running making heat, the Prius uses it to charge the battery. This extra charging will sometimes run the battery into the green zone.

3) Force charging. If you hold down the brake and the accelerator pedal, it will force the Prius to run the engine and charge the battery. Obviously you can use this to force the battery to a green state.

Don't be fooled into thinking green is good. Green isn't bad, but it's not good either. It just is.

Tom

 

perhaps you are making the same mistake I did when mine was new.
Its misleading that they list the fuel tank as being 11.9 gallons, because in reality it is more like 10 gallons and 9 in the winter.

 

I realize that. Why Toyota chose green for what amounts to excess charge is a mystery to me. I'll bet if you asked 100 new owners who had not searched the net for this sort of info, the vast majority would think green was best and that they should be targeting it.

Yep, but it will do it on short steep hills with lights at the bottom too (or a series of these.) Keep in mind throughout that I'm observing this with a warm car in warm (not hot) weather so it is not a warm up issue. I'm still scratching my head about why this is happening at times. I can't seem to burn off the charge on the next short steep climb despite trying to do so, instead it applies the ICE too quickly. It's like it is adding charge at roughly twice the rate it is using it. Yes, I'm doing a good job of recapturing with regen before completely unavoidable stops, but I wish it would let me burn that charge preferentially on the climb, rather than gaining charge.

Hmmm, haven't tried this...might be handy when I eventually do some mountain climbs, building charge this way in prep for a long hill.

 

most likely you stayed in green because you didn't get stuck at a stop light. You probably charged just as much as normal, but never had a chance to deplete any because you lucked out and didn't have to accelerate (uses the most energy) from stop. Other factors that could have contributed could have been that the outside temp was lower and you either had the A/C turned off or the Auto mode didn't need to run the compressor. The battery also has an optimal temperature where it is most efficient which seems to be somewhere between 60 and 75 degrees.

 

Re: Purple Battery Lines

Initially you were operating in an area that didn't require the engine, so the electric motor draws down the battery. Once the battery got low, the engine had to come on to recharge. Once started, the engine is used to power the car and recharge until the battery gets back into the preferred zone.

Tom