Half a croissant, on a plate, with a sign in front of it saying '50c'
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And miles? to go

Before I run out of fuel
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I know how my car’s fuel gauge works. I know it’s consistent. But, sometimes I just want to SEE how much fuel is left in the tank. (Latent control-freak tendencies perhaps?)

It’s probably just me, but I’d like to have a camera and safe light source (white LED’s, fiber optics, whatever) in my fuel tank with a dash mounted display to enable seeing how much fuel is really left in there.

It might be helpful for those with a propensity to “run on fumes” to know if they need to stop at this corner or can make it one more block to the next corner to refuel.

(And yes, I know about the damage done to certain fuel pumps by running low on fuel.)

half, Feb 19 2003

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       Ah, but then you have to put a light in (or make the gas tank transparent and hope the sun is shining). I never understood the concept of putting the fuel pump in the gas tank so I'd be disinclined to buy a car like this. The fewer spark sources submerged in my propellent the better.
phoenix, Feb 19 2003
  

       But how will you know for sure that the fridge light is off when its door's shut?
-alx, Feb 19 2003
  

       A better way to do this would be to link a GPS system, real-time traffic information and a map detailing terrain plus the location of petrol stations. This way you would have a reasonable chance of estimating whether you absolutely have to buy more petrol.
Aristotle, Feb 19 2003
  

       Fuel tank mounts or suspension points with integrated strain-gauges that weigh the tank continuously?   

       Or a crude sonar system thingy that taps on the tank side and "listens" (and analyzes) the sound pitch of the tap and looks up remaining fuel in a tank-tap-pitch to fuel-volume lookup table? ;-)   

       Float-based system with 4 or more floats placed around the tank of which the average is reported? Maybe the float could be a sheet that lays on the surface of the fuel, getting a better "picture" of the remaining volume.   

       Bladder tank liner within a pressurized tank wrapped in ElekTex fabric that reports the bladder volume? (The pressurized bladder could also, maybe, take the place of the fuel pump? Lore has it that VW Beetles of a certain long-ago vintage pressurized their tanks with a small tube that ran from the valve stem of the spare tire to the fuel filler-tube cap.)   

       Vapor-detection transducer with a computer that calculates fuel volume based on exactly how much vapor is detected in the tank?   

       A system that drops instrumented bluetooth-equipped marbles from the top of the tank and bases its remaining-fuel calculation based on how long it takes for the marble to impact the bottom of the tank?   

       A movable wall in the tank that, when actuated, "squeezes" the remaining fuel up until it touches a liquid-sensing transducer in the ceiling of the tank and then calculates how much fuel remains by how far the wall had to be moved?   

       A precise illuminated grid pattern mounted in the ceiling of the tank and read by an image sensor in the bottom of the tank that "sees" how much fuel is left by calculating how much refraction it is seeing in the grid? (Okay, that's a stretch . . . maybe interferometry or something?)   

       An articulated fuel-sump that can be raised just until it begins to starve (as measured from an instrumented fuel pump) and the remaining fuel amount is inferred from how far the pickup point had to be raised before the starvation began?   

       A system that sets the fuel afire and tells you how much fuel was remaining by timing how long it takes for the remaining fuel to burn up? This needs a remote display, of course.   

       And, finally, a wee fuel elf that lives in your tank and calls you on her tiny cell phone (a fuel cell?) and tells you that you had best be pulling into a gas station?   

       <apologies for the sustained upspeak>   

       Oh . . . "before I sleep."
bristolz, Feb 19 2003
  

       Around the M25 in London it would be quite disconcerting to start off with 200 miles to go and just sit there, not moving, watching the miles count slowly down to 0.   

       Like [dag] I'm sure I've rented cars in the US that have this facility.
PeterSilly, Feb 19 2003
  

       [phoenix]: //safe light source (white LED’s, fiber optics, whatever)// can't be much worse than actually pumping fuel _through_ a brush-type motor.   

       [dag]: they are common. I just want to see.   

       [-alx]: 'zaktly   

       [bristolz]: Heh. "tap-pitch to fuel-volume".
"Have you lost your marbles? Why, no. They're in my gas tank, silly."
I had never thought about using a pneumatic pump to pressurize a fuel tank. But, now that you mention it, aside from obvious issues, it does have a certain appeal. I can carry my little bicycle pump in the glove compartment for the inevitable fuel pump failure event.
half, Feb 19 2003
  

       [bristolz] I may be wrong but I think the "small tube that ran from the valve stem of the spare tire on a VW" was used to work the window washer. yes? (i.e. don't get a flat after cleaning your windows a lot)
crabbie, Feb 19 2003
  

       Ooops. I think you are right. I mis-remembered the lore, apparently.
bristolz, Feb 19 2003
  

       [crabbie]I may be wrong but I think the "small tube that ran from the valve stem of the spare tire on a VW" was used to work the window washer. yes? (i.e. don't get a flat after cleaning your windows a lot)   

       My parents had a VW Beetle. It was indeed the windshield washer. Nowhere near enough volume for the gas tank (it takes most people months or years to go through a gallon of windshield washer. It doesn't take nearly as long to go through a gallon of gasoline).
supercat, Feb 19 2003
  

       "Mandatory half-hour reserve"
8th of 7, Feb 20 2003
  

       You could periodically, stop, lift the filler cap and look in (no naked flame illumination please).   

       But seriously, visual indication is less reliable than calibrated guages. The problem is that the tank may not be a consistent shape and the level may be misleading. Also looking down into a tank tells you not much at all.   

       I's doubt that safety specs would suit a visual inspection because of tank material requirements, location of the tank and the distraction factor.   

       I have flown Quicksilver MX's - the only vehicle I have seen with a see-through tank and no guage. Trust me when I say the system can be deceptive.
FloridaManatee, Feb 20 2003
  

       If the gas tank was transparent, you could make it into the windscreen (US: windshield), then, as you drove along, peering through the petrol sloshing about before your eyes, you'd always know how much you had left.
hippo, Feb 20 2003
  

       OCD-Cam: check the lights/ gas are still off and the doors locked at home from the comfort of your car.
whimsickle, Feb 20 2003
  

       completely transparent cars would be handy even for those (like me) who only understand the windscreen wash container and the oil dipstick. I waited for an AA man for an hour the other day when the car started making one hell of a banging - please don't ask what it was <highly embarrassed>
po, Feb 20 2003
  

       Why would the American Auto Assoc. have an office in the UK? (btw, happy baker birthday, dag.)
waugsqueke, Feb 20 2003
  

       Automobile Association. not telling, don't make me. happy hb birthday to you.
po, Feb 20 2003
  

       My car manual says it has a 10 gallon tank of which 8 gallons is usable capacity. I don't know how that fits into this discussion, or indeed what it means.
pottedstu, Feb 20 2003
  

       It means the last 2 gallons are water.
bristolz, Feb 20 2003
  

       new saab cars already have this feature, or has someone already said that? it's baked anyway...
iain, Feb 20 2003
  

       //10 gallon tank of which 8 gallons is usable capacity...indeed what it means//
Most likely the fuel pick-up won't reliably extract the last 2 gallons. Seems like a lot of unusable fuel for a 10 gallon tank. It may just be that the fuel gauge shows empty or the reserve light comes on at that point.
  

       If you had a camera in your fuel tank you could know for sure.
half, Feb 20 2003
  

       And where to position the camera? Maybe the last quarter inch/few millmeters, so tha twhen you see the miniscus, you know IT's TIME
mook27, Feb 21 2003
  

       That would mean you have to constantly check. If a light sensor were placed inside the window, it could be used to trigger a liitle orange light on the dashboard (maybe in the shape of a fuel pump?) to tell you it was time to think about refuelling.
egbert, Feb 22 2003
  

       // The fewer spark sources submerged in my propellent the better. //   

       Surely they're perfectly safe if they're submerged: it's fuel + air which is flammable / explosive, not fuel alone.
JKew, Feb 23 2003
  

       [JKew] entirely correct; but it seems we're dealing with the sort of bozos who are determined to try and run their vehicles on fumes - a foolish and unnecessary activity.   

       The "submerged spark gap" issue is an interesting one; depending on how much oxygen is dissolved in the fuel (I'll have to check on the figures) it might still be possible to trigger a "flame bubble" within the volume of the liquid and so engender a catastrophic fire, if the spark were sufficiently energetic. Some very early Marconi spark-gap transmitters used an oil-quenched arc but the oil would probably have been much thicker and proportonately less flammable. Hmm, I shall definitely have to look this up.
8th of 7, Feb 24 2003
  

       I never run any of my cars on fumes. I'm not a fan of replacing fuel pumps or pushing cars in to gas stations.   

       Since tearing apart a dead in-tank fuel pump, I've been curious as to why there aren't explosions when the last bit of fuel is sucked out of the tank and the surrounding air-vapor mixture is exposed to the sparks from the commutator/brushes of a permanent magnet motor. 8th?
half, Feb 24 2003
  

       Did [iain] suggest that new Saab autos come with the banging noise already built-in, or was that the tongue-biting feature? I'm confused.   

       Again!
Canuck, Feb 26 2003
  

       Why not just put a flowmeter on the gas line?   

       A chip could keep track of how much you've gone through, maybe even give you a neat little graph to look at! This'd also be interesting to me since I've always wondered about instaneous gas-mileage as opposed to the average kind I calculate when I get a new tank.
rapid transit, May 21 2003
  

       Let me help you all. Here is how it can be done, cheaply, and reliably.
1. Drive car until it runs out of gas and will not go.
2. Remove 12 oz. glass bottle of gas from trunk and pour it in the tank.
3. Reset odometer. Now again drive until the car runs out of gas.
4. Now you know how many miles a 12 oz bottle of gas will get you. Remove second 12 oz bottle of gas from trunk and hope that it is enough to get to gas station. Actually, now you will know for certain whether or not it is enough.
5. At station, refill both 12 oz bottles of gas and store them in trunk for future use.
bungston, May 21 2003
  

       Or how 'bout a computer graphic image of how much fuel you have in your tank, complete with rippley liquid surface effects.
sartep, May 21 2003
  

       And a little fluffy cloud background! With a highly polygonal robot rising out of the water, then dancing on its surface, then have a dragon come off from the side, have the camera spin around it, then have something that sort of looks like a fish jump out of the water and make a fish-like gesture, then morph into a submarine, then follow the submarine around to an underground city in your gas tank where elves live and ...   

       *gasp*   

       I've been watching too many oldschool CGI reels lately, methinks.
rapid transit, May 22 2003
  

       Ever see Waterworld? They're like the guy at the bottom of the oil tanker.
RayfordSteele, Jul 13 2003
  

       I can't wait any longer [po]. What was the loud banging noise?
methinksnot, Aug 31 2006
  

       I thought of this idea this morning, after paying a huge amount of cash to finally replace an in-tank unit that included the fuel pump and the gas-guage sender.   

       I've been driving around using the trip odometer to estimate fuel remaining, and would have liked to have had a camera in there. It couldn't add much risk to the electronic mishmash the tank already has in it.   

       I did come up with a retrofit/add-on that would be a little safer, maybe. It's a light and camera unit that fits in the gas-filler opening, replacing the gas cap, with fiber optics running down into the tank proper.   

       But then, that puts all the sparks up where the fumes meet the free air, so that's bad. Plus, the cable would be in the way when you fill the tank.   

       I do think that a camera installed inside the tank would work out fine. Some of the objections in the annos above assume that the cars is sitting still--if it's moving, there's going to be sloshing, which will be easy to see.   

       And seeing the sloshing is very good, as the best way to get every drop of gas out of a tank is to slosh it around. (I learned this when I was in a vehicle that ran out of gas. One guy hopped out and started walking to get gas. Another guy rocked the vehicle around and started it up again. We drove past the guy who was walking and didn't pick him up.)   

       Those folks who say you should never let the tank go below half-full to avoid burning out the in-tank fuel pump are probably right. But dammit, I hate poor design so much that I refused to do it. Sad, innit?
baconbrain, Jul 22 2007
  

       Yes, [po], please do tell. We've been friends long enough that you know we won't tease you. And I told the story of how I demolished my truck.
normzone, Jul 22 2007
  

       added 2 embarrassing stories to my list since this!
po, Jul 22 2007
  

       Maybe you should just get a little horse. Then you could just look to see what was in his nose bag.
nomocrow, Jul 23 2007
  
      
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