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VSC + Fuel Gauge Temp Observations! + 165 miles & still

Discussion in 'Gen 2 Prius Main Forum' started by benbethel, Mar 6, 2004.

  1. benbethel

    benbethel Junior Member

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    I drove from Phoenix to Flagstaff (140 miles) Thursday and on the way there was tons of fog, then sleet, and snow – there were 12 inches of snow! I’ve never driven in fog, sleet or snow before, it was quite nerve wracking! I kept thinking I was going so slow, but my car is so darn quiet that I’d look down and I was doing 50-55mph! The vehicle skid control only kicked in a few times, and it was really need how I could feel the car pull and correct itself (almost like a lurching feeling sometimes) and not let me skid in the ice…. It was very strange but very comforting.

    On the way up I only got 38.5mpg, but then again I was going from 1200 feet to 7800 feet in elevation over the 140 mile drive. When I got up there I had only 1/4 of my tank left - the temperature had changed from 70 degrees to about 34 degrees during the trip, so the temperature sensor in the fuel tank seems to be the problem, not the bladder folks!

    On the way back I got 52.5mpg, and that was in perfect weather with temperatures from 34 degrees to 58 degrees, and with my speed always at about 79mph. Lots of downhill stretches, but a few huge uphill ones too! My battery would go from just one bar remaining to full bars in a period of about 10 minutes!

    My tank is 11.9 gallons but never takes more than 8.5 gallons when the empty light is flashing, which is frustrating – I think I should be able to go almost 600 miles between fill-ups and not 400 miles!

    But, check this out, I followed some of the Prius “experts†advice and filled my tank, then filled it slowly all the way up after the pump initially stopped. I made a huge mistake and about a cup of fuel spilled out of the car. I know how bad this is and feel very guilty and will never do it again! But the weird thing is that the tank took about 9 gallons of fuel, when I know that I'd only driven about 250 miles (did a long day trip to two national monuments) on this tank at an average of around 40mpg.

    Well, I have now driven 165 miles and not one single bar on the fuel gauge (out of 10) has disappeared yet! What’s up with that?! I need some explaining on this!

    My guess is that the temperature when I left Flagstaff was around 39 degrees, in Phoenix right now it's around 70 degrees. So, going from warm to cold the gauge dropped very, very quickly. And now I've gone from cold to warm temperatures and have driven 165 miles and not one bar is gone on my fuel gauge.

    So, the thing is this: if the fuel gauge is temperature sensitive, does it also control the fuel bladder somehow? If this is the case, then it seems smart to fill up your car only when it's the coldest time of the day, as it'll take more fuel.

    Toyota needs to correct the temperature sensor on the fuel gauge - it's just not accurate.... this really seems like the problem here. In the meantime, I'll continue to refuel only when I've driven 11 X mpg, which should be safe... If I'm getting 45mpg (my usual average) then I'll drive 495 miles - I'll say 500, and I should still be fine.

    What does everyone think of this? Interesting?

    Ben
     
    #1 benbethel, Mar 6, 2004
  2. efusco

    efusco Moderator Emeritus
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    That's really bad that you had the VSC kick in at all, you were near to crashing. Driving in snow/sleet/wet IS unnerving but you mustn't ever let your vehicle get up to those kinds of speeds or in a situation that the VSC would kick in. Think of the VSC like you would the air bags, they only are used in emergency situations.

    I think 38.5 is excellent MPG considering the circumstances. I'll ask again later, but I do not understand what you're trying to say or how you reached your conclusion about the temperture sensor being "the problem" I think you need to elaborate a lot here on what you mean and how you reached your conclusion.

    Sounds about right.

    Old news, persistant frustration....get used to it.

    Yea, bad. It's easy to force fuel in under pressure, but that pressure's gotta go somewhere when you pull out the plug keeping it in (fuel nozzle).

    You forced excess fuel into the tank. No suprise. It'll start going down soon.

    The bladder is a bladder, nothing 'controls' it. Think of a hot water bottle inside a metal container.

    If your goal is to get more fuel into the tank then it's smarter to fill in the warmest tempertures. The bladder will be more expansile and you'll increase the volume of fuel added. Cold temps the bladder is less flexible and won't expand as much and thus less fuel.

    What are you talking about? I'm completely confused about how you've reached this conclusion. It may be the right answer,but I don't know how you've arrived at it. My personal belief is that the problem has to do with the variable size/volume of the bladder and since there is no weight sensor it's much more difficult to accurately determine the fuel volume when it starts getting low.

    I think that's a very very risky plan. If your temps are consistantly 70 degrees then you may be OK, but if you filled up when it was 34 degrees out you may have only gotten 10.5 total gallons in and you'll run out of gas 20-30 miles before you reach time to fill up. Worse scenarios are possible b/c not all the volume of fuel is usable, there is a small reservoir for keeping the fuel pump cool and not all will be accessible.

    using 10X mpg is more likely to be safe, though still some risk depending on circumstances. John1701A likes to recommend a very conservative 9X mpg.

    What ever you ultimately decide to do I suggest waiting until you've got a couple thousand miles on the car and are more confident in the tank volume and volume of usable fuel before you commit to anything too risky/radical.
     
    #2 efusco, Mar 6, 2004
  3. benbethel

    benbethel Junior Member

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    Cool - thanks for the reports... so, the temperature gauge inside the fuel tank does have an effect on the fuel gauge, but that's it... it has no effect on the bladder. I hope I got that right. And I was able to get a LOT more gas in the tank just because it was cold out, or perhaps because I was at 8000 feet in elevation? Ahhh.... maybe that had a lot to do with it. I was just thinking of the temperatures!

    I've driven 5,000 miles on my Prius since taking delivery in October.
     
    #3 benbethel, Mar 6, 2004
  4. efusco

    efusco Moderator Emeritus
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    I repeat, that does not make sense to physics or other reported annecdotal experience. Cold will reduce the bladder size/volume and expansibility. Thus, under the same conditions (same pump cut off point, same pressure, same distance nozzle inserted, etc) you will get more fuel in in warm conditions. I still feel the only reason you got more in in the cold climate was b/c you forced it in.
     
    #4 efusco, Mar 6, 2004
  5. Wolfman

    Wolfman New Member

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    Benbethel, when you are topping off, pull the nozzle out, and reinsert only the first 1/2" or so back into the filler neck. When I'm filling, I easily hear and see bubbling around the rubber seal. I made a mess a couple of times getting the procedure right myself.
     
    #5 Wolfman, Mar 6, 2004
  6. rockluvr

    rockluvr New Member

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    Evan,
    I thought the bladder is INSIDE of a fixed tank and the purpose of the bladder is to reduce space within the fuel tank so that there are less gasoline fumes i.e. gasoline vapor in the tank that could come out when refueling or during driving. THEN it seems to me that for cold temperatures as you stated
    , the fuel tank would accomodate MORE fuel since the bladder would be taking up less space within the fuel tank. PLEASE correct me if I am wrong about how the bladder works - I would really like to understand this.
     
    #6 rockluvr, Mar 6, 2004
  7. Ken Cooper

    Ken Cooper New Member

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    Another perspective on incorrect readings regarding remaining fuel:

    Just out of curiosity sake, is the fuel pump on the Prius in the gas tank as it is in so many cars these days?

    The reason I ask is this (using my current Audi A4 as a reference): When there are about 2 gallons of fuel left in the Audi the gas gauge will read empty and the computer will tell you that that you have zero miles of driving left on that tank of gas. I might add that I've had occasion to, not by choice, drive several miles under these "zero" conditions (a situation that can induce words of prayer and, I think, affect blood pressure).

    With the fuel pump in the gas tank, it relies on the gasoline for cooling and lubrication. If you run out of gas it's bad for your fuel pump, and it can be bad for your fuel injectors.

    From what I've read on the subject, car manufacturers go to great lengths these days to protect us from ourselves by fibbing a bit, prevaricating for purposes of minimizing the probability of our running out of gasoline (for the reasons mentioned above).

    Anyhow ... Food for thought.

    Ken
     
    #7 Ken Cooper, Mar 6, 2004
  8. benbethel

    benbethel Junior Member

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    Well, one thing I also noticed was that it only took 1/2 a gallon before the fuel started spilling out, again this was at 8000 feet and about 35 degrees... usually I'm at 1200 feet and 70 degrees and I can go for a good 1.5 gallons without ever having fuel come to the surface! As a matter of fact, when I'm at 1200 feet at 70 degrees I can sit there and click-click-click the nozzle away for a good 15 minutes and I'll never get to the top. When I was at 8000 feet and 35 degrees yesterday it only took about 30 seconds to get that 1/2 gallon in and start spilling fuel... strange.

    Oh, and on the VSC comment from Evan about being close to crashing, I'll have to dispute that as well. Here in Phoenix I'll have the VSC light flash at least once a day - there are specific intersections where it's bumpy and the VSC always engagages... I can name a few of them. Also, my neighbor has his VSC engage at those intersections as well. I think the VSC engaging in the ice/snow just meant that I hit a few slippery patches, and it would have engaged at a slow speed on those spots as well.
     
    #8 benbethel, Mar 6, 2004
  9. efusco

    efusco Moderator Emeritus
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    The fuel goes into the bladder, not around it. Think of it more as a tank liner.
     
    #9 efusco, Mar 6, 2004
  10. efusco

    efusco Moderator Emeritus
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    No, that is NOT the VSC, that is the TRACTION control (car with wiggly lines below). That WILL, indeed, kick in fairly frequently (too much IMO), esp. when accelerating from a stop on slick pavement and, as you mention, with certain bumps if you're going fast enough that the wheels spin a little making the computer think the car is losing traction.

    The VSC should almost never come into play. It is triggered by YAW and lateral movement in relation to wheel rotation speed and is used for recovery from slides and over/under-steering situations. A special tone will be activated and VSC will light on the display (you'll probably never see it b/c you'll have been fighting to keep the car on the road not studying the dash).
     
    #10 efusco, Mar 6, 2004
  11. RobertO

    RobertO New Member

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    Add to the physics of the fuel Bladder System;

    Barometric Pressure.

    For every 100 feet of altitude gain, everthing about your car (including you) will be inclined to expand n[/n]%; the reverse occurs as you go back down.

    Fuel and bladder are very like to expand more at 4-5,000 feet.

    Just a thought.

    I've had two dealers here in the Pacific NW tell me that the frequent low barometric pressure we have here in the winter dramatically affects all gasoline engines with respect to MPG.

    Imagine the difference between Death Valley and Pike's Peak, for example. I'd be hard pressed to imagine no difference in configuraton, horsepower, combustion efficiency and, by inference, MPG.


    Bob
     
    #11 RobertO, Mar 6, 2004
  12. benbethel

    benbethel Junior Member

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    Ahh... traction control - yes, that's it! Sorry about being confused over that and the VSC. My bad.

    So, the fuel goes INSIDE the bladder? Now that's strange, but it does totally make sense. Every bag of chips and bottle of anything is HUGE by the time I get to Flagstaff (8000 feet) so no wonder the bladder could hold so much more fuel and why I'm now at 185 miles with zero bars gone from the fuel gauge. 10/10 are still there... crazy!

    Interesting. I want to see a picture of this bladder... is it rubber?
     
    #12 benbethel, Mar 7, 2004
  13. Tempus

    Tempus Senior Member

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    I've never actually seen a photograph of the bladder. That would interest me too.

    Yes, the fuel goes inside the bladder, just like going into a balloon.

    It's part of the Evaporative Emissions Control that gives the Prius the PZEV emissions rating. That means that when the Prius is sitting still, no gasoline is out-gassing, at least partially because the gasoline is all contained in the big baggie in the fuel tank.

    Oddly enough, outside the US some Prii do not have the bladder. That's one of the many differences between the various international versions.
     
    #13 Tempus, Mar 7, 2004
  14. rockluvr

    rockluvr New Member

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    Thanks, Evan, for the information about the bladder.

    As far as altitude, in Denver at ~ 5400' I have not gotten more than 7.6 gallons in the tank (with one bar flashing). I will be interested to see how the tank changes with summer temperatures.
     
    #14 rockluvr, Mar 7, 2004
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