Gen 3 Fuel Guage

[kevin h]

The Gen 3 is now 2 1/2 years old with 26000 miles under its belt.

Until recently, I would fill up and the miles left in the tank would read about 600 miles (usually a bit more) and I'd get anything between 500 and 550 miles before the gauge was down to one bar and I'd fill up again.

Well, earlier this month I took a 520 mile trip to Germany, filled the tank to the brim a few days early and then topped up by 6 liters on the day we left. The miles available did not change from a reading of 530 miles

Did the 520 miles, with the last 10 miles on a flashing fuel gauge and filled up.

The mileage available now only went up to 550 miles and after 450 miles I feel the need to fill up again (one bar), but the amount of fuel going into the tank is less.

I'm still achieving the types on MPG which should allow me to do 550 miles before the gauge reads only one bar, but the guage seems to disagree.

Any ideas.

At the moment the fuel gauge is telling me to fill up about 50 miles earlier than it should, and thats allowing for the small drop in MPG due to the colder weather. (68 mpg today on a 40 mile country run but it was 13 deg'c)

[timberwolf]

You've already said what caused it i.e. you shouldn't have done the 6 litre fill-up. Sorry, I don't know how to correct it, I think it will correct itself eventually, or you could try run 50 or 100 miles into empty and then fill-up.

It is also not a good to brim the fuel tank, only fill-up to the first click because if you flood the charcoal filter too often, it will have to be replaced.

[Jan&tone]

When you fill up, the sensors work out how much you put in compared with the miles travelled since the last fill up. That figure is extrapolated to give you the new range.

Therefore the lower the miles travelled between fills the less the range will show.

For this reason there is absolutely no point in even looking at the range display, it will rarely be accurate.

If you are averaging 60mog you know that you have a range of 600 miles, personally I always fill up when there are 3 blobs showing on the gauge, that way I will never run out of gogo juice regardless of what the range says.

[Chris Dance]

I always fill my car to the brim. I do not know about the charcoal filter any more info on this timberwolf I would be obliged. I rarely let the fuel in the tank go below gauge indication of a quarter.

[Uncle Buck]

Strangely enough, this is an issue with the Auris too. The one bar left & flashing scenario persuaded me to fill up yesterday, only to find out it still had over 2 gallons in the tank. I know this because of the amount I put in versus the tank capacity. Therefore (in theory) I could have done another 50-60 mls easily w/out worrying about running out ......

[timberwolf]

I always fill my car to the brim. I do not know about the charcoal filter any more info on this timberwolf I would be obliged. I rarely let the fuel in the tank go below gauge indication of a quarter.

For example, in the log entry dated "8-10-2005 Marathon MPG, part 3." in the following link Prius-log214

Edit: addition below:

And another link with an exploded work shop diagram for the Gen 3 this time!

Prius fuel filter

Xmas competition locate the part. I wonder how long it takes to get to it?

[Joseph D]

... I would fill up and the miles left in the tank would read about 600 miles ...

I have not seen a miles remaining countdown on my Prius. Where can I see that?

[Jan&tone]

... I would fill up and the miles left in the tank would read about 600 miles ...

I have not seen a miles remaining countdown on my Prius. Where can I see that?

Push the 'trip' button on the wheel and It will cycle through trip a, trip b, etc... Can't remember which one is the remaining mileage, but that's where you find it.

[GreenJuice]

... I would fill up and the miles left in the tank would read about 600 miles ...

I have not seen a miles remaining countdown on my Prius. Where can I see that?

The 'distance to empty' display is a feature on the Gen 3 Prius, AFAIK not available on the Gen 2. I used ScanGauge when I had my Gen 2, and now with my Gen 3 it interestingly gives a different figure when compared to the car's computer (see more below). You can also figure it out in your head, if reasonably good at mental arithmetic, as the Gen 2 and Gen 3 Prius both have 45 litre or 10 Imperial gallon tanks - so if your indicated MPG is say 55 mpg, you would expect to get around 550 miles on that tank [note: other readers have posted that the indicated MPG is generous by about 5%, so you may need to take that into account].

When comparing the Gen 2, Gen 3 and ScanGauge I have noted the following behaviour and this information from Priuschat:

1. Gen 2 - Fuel gauge is not all linear. The first 'pip' can take around 120 miles before it disappears, each subsequent 'pip' appears to be consistently linear (around 45 - 50 miles each).

When the last 'pip' starts to flash, you hear a beep and the car briefly displays 'Add Fuel' on the MFD screen (if you have one). At this point, it is reported that you have a reserve of about 6.5 litres. Using Scangauge as a guide, I have gone up to 40 miles further before refuelling. Taking driving conditions into account, I would say 20 miles is well 'safe' (this statement ignores any potential fears that others may have about 'dirty' fuel at the bottom of the tank or keeping the fuel pump immersed and cool). Others have driven on until completely out of fuel. At that point, they report that you will see the 'Check Engine' warning light come on. The car will run on the traction Battery until it is 'indicated' flat which is actually about 40% state-of-charge (SOC), essentially in forced EV mode. Various figures of 1/4 to 2 miles have been quoted before this is flat, so essentially you have a little room for manoeuvre to get somewhere safe.

2. Gen 3 - (I have less experience in this car and happy to be corrected!). The fuel gauge appears to be more linear than Gen 2, with each of the ten 'pips' representing about a tenth of 'available fuel'. I put this in inverted commas because, like the Gen 2, the indicator works to a 'reserve' so Empty is not actually Empty. Reports indicate that the Gen 3 reserve is about 8 litres (or 1.75 gallons, 2.1 US gallons). The car's 'distance to empty' gauge counts down to this point as zero, and will continue to show zero when using your reserve. This gauge appears to me to always count down from the moment the tank is filled (unlike the ScanGauge figure, which goes up and down depending on how I drive). This tells me that the car is using a previous MPG figure to calculate the distance to empty, whilst scangauge uses the current average MPG (since last reset). Others have driven on to a complete stop and their reported findings are in this long post & discussion. (I should warn you that the discussion is currently 45 pages long and mostly opinionated drivel with a handful of gems of information! Best value is the experimental work by Bob Wilson who did the run-to-flat experiment on this Gen 3 five times by the end of the thread!).

In summary:

i) The low fuel indication is a beep and the last 'pip' flashing. Distance to empty gauge indicates 20 miles (in my experience).

ii) The larger reserve could get you another 100 miles (around 120 if you are Bob Wilson)

iii) When you run out of fuel, unlike for Gen 2, you **do not** get a 'Check Engine' warning light. Instead, the car seamlessly transitions into using the traction Battery without telling you. The only indication you might have is a feeling of reduction in power if travelling at over 46 mph. At lower urban speeds it may be so subtle that you may not notice anything. If you happen to have the Energy Display selected, it will show no arrows. Therefore, this is the display to select if you are deliberately going to run your reserve to empty. When the arrows disappear, you only have traction Battery power. If you miss this, the car will run on traction battery until 'indicated flat' (actually keeping a charge reserve to protect itself). At this point, the car will stop without warning. The only indication is the 'Power Steering fail' light. All power to the wheels is cut and the car shifts itself to (N)eutral and you are unable to engage (D)rive. Therefore, unlike Gen 2, there is a greater chance of missing these subtle signs and the car just stopping without giving you the chance to get to a safe situation.

Hope that helps!

[timberwolf]

... I would fill up and the miles left in the tank would read about 600 miles ...

I have not seen a miles remaining countdown on my Prius. Where can I see that?

Don't worry you haven't missed an option or setting, it's a 3rd Generation feature.

[timberwolf]

<snip>

fuel. At that point, they report that you will see the 'Check Engine' warning light come on. The car will run on the traction battery until it is 'indicated' flat which is actually about 40% state-of-charge (SOC), essentially in forced EV mode. Various figures of 1/4 to 2 miles have been quoted before this is flat, so essentially you have a little room for manoeuvre to get somewhere safe.

<snip>

Hope that helps!

Has the quirk/bug about being able to run Gen 2 HV Battery dangerously below the 40% SOC been disproved?

Edit: By dangerous, I actually mean that you could breakdown and will require a tow, and either a recharge of the HV Battery or replacement of the HV Battery.

Edit2: It looks like I may have got this mixed up with the Classic (Gen 1).

BTW Nice informative post.