Strange Happenings with my Gas gauge

millerjl26,

I think I noticed something similar on a recent long trip. I could not replicate it, but I seemed to notice the phenomenon when I was either going up or down a hill. So, maybe the fuel sensor is affected by the car not being level.

 

this can be due to the shape of the fuel tank and where the sensor is located.... remember that the previous Prius had a bladder tank which would be affected differently...

 

I've seen the same behavior in a previous car, so it's not just the Prius.

 

I've noticed this "phenomenon" (don't know what to call it) too. The fuels bar disappear, then reappear, seemingly out of nowhere. Over the long run, they'll gradually drop one by one, as they should. But intermittently I'll see one bar go away and come back. It looks odd, but I'm sure there's a good explanation for it.

 

fill the tank up to the top of the neck where you can not pump anymore fuel without it going on the ground.

Than watch your guage, strange things will happen also.

Like, driving over 200 miles and the tank is still full.

alfon

 

Going down hill the regenerative braking refills the tank. Sorry, we all know that's not true, but the setup was irresistible.

Tom

 

Is that why I have to stop and let some gas out of the tank every so often?

 

We saw something like this on the 09 we rented earlier this month (reason we now own a 2010). Our first leg of the trip and the gage acted "normal" being about 50 miles or so per bar.

The second fill-up had me driving and I went over 130 miles before a single bar dropped. In fact I think we went around 200 mi on the first 2 bars.

 

Yes it is. On long downhills we try to travel with a Hummer, where we can offload excess fuel.

Tom

 

[Smacks forehead] Tom, I walked right into that one. Too funny!

 

We just returned from our first lengthy trip (650 miles) in our 2010 Prius IV. Fuel gauge was acting perfectly normal dropping one bar at a time for the first three bars (and should have been close to dropping another bar). Then after going around a curve to exit one highway for another, it suddenly was full again! It stayed full for about 3-4 miles, then dropped one bar, then another. We reached our destination. Turned the car off and left it overnight. Next morning, it was back to three bars down. Has anyone else experienced this behavior?

 

it happens to me. i think its normal or not a big deal. Might just be the way the sensor works and its sensitivity regarding the top bars.

 

The sender in the gas tank is a simple variable resistor, most likely a wire wound one. The cars electronics interpret the variable resistors resistance and shows you a number of bars. If it is right on the verge of switching from 10 to 9 bars, it is reasonable for it to go back and forth under some conditions.

So far in 1100 miles I have observed mine go from 2 to 1 then back to 2 bars once. A change in grade, going around a corner or accelerating or stopping can all have an effect on fuel level reading.

Toyota electronically (or via computer) damps most, but not all of the variation out.

If that changing only happens between two adjacent numbers of bars and the indication doesn't bounce back and forth rapidly, I don't think your gauge has a problem.

I haven't experienced that with a Prius, have seen changes that big on cars with regular analog gauge readouts. See if you can repeat the problem. It would be a good thing for all of us to know. Was it a long turn taken at a fairly high speed?

The slow return to normal sounds like Toyota has a lot of damping in the system (most likely in the computer) to protect us from seeing what the sending unit is actually saying.

FWIW, The specs for the fuel sender are 405-415 Ohms at Empty and 12-18 Ohms at full.

 

It was indeed a fairly long turn (I-71 North to I-480 West for those that might be familiar) but I did not take it very fast at all. Will keep an eye on this and post if it ever happens again.

 

Three bars? Not noticed on mine. But two bars has happened many times, particularly 8-10-8.

If you have a ScanGaugeII, program in the FLV XGauge. It will reveal considerable sloshing around in the tank. The dashboard display filters out most of the slosh, but not all of it.

This is really no different than every analog-gauged non-hybrid I have owned.

 

Its completely normal. Imagine the fuel sensor as a little float on top of the gasoline in the tank, off to one side. When you go down/uphill, the gas in the tank tilts and momentarily raises or lowers the level at the sides. Youll notice this especially if you park on a decent incline - the initial reading will be "incorrect", and it will shortly correct itself and add/subtract bars as you get driving.

This is also why it takes a while for that first bar to disappear, or why a traditional analog gauge stays full for the first gallon or two - the float cant move down until the gasoline level has receded to the point where the float isnt completely submerged and stuck at the top.

 

I've seen this with my gen III, and every analog gas gauge I've owned--just attribute it to 'slop' around in the tank as it begins to empty. As Prius ownwers, we pay more attention to these things, and also there is the (inaccurate, imo) tendency to assume "digital=better." I suspect the bladder in the gen II kept this from happening.
~T