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Discussion Starter #1
I was thinking about stale gas. It is odd what runs through my mind on a weekend. :p I think the Volt will really need a very accurate gas gauge to help me avoid stale gas. During most weeks I would like to run around town on a nearly empty gas tank using just what I have in the batteries (why carry extra weight). However, I will go on a trip out of town and may have to run exclusively on gas since I doubt hotels will let me run a power cord to my car. On my return I want to burn the gas down to about a gallon or less. Thinking about today's gas guages that would be impossible to know since you never really know when you hit botom. Idiot lights don't help you predict when empty will happen and gauges are not much better.

What would be cool is if the Volt had a drain-the-tank feature. I charge up the batteries but the Volt keeps them topped-off by running the ICE until the gas tank is down to some minimum level and then it goes into normal operation. Then to avoid stale gas I drop and extra gallon or two in every couple of months and re-run the drain-the-tank feature. This would probably be good for the ICE; cleans out the fuel system, churns up the oil, moves the coolent around.
 

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Here's another thought... It really bothers me that fuel guages are analog. How about an digital guage that showed remaining fuel in tenths of a gal. Then, when I push the "Fuel Rundown" button, I can turn it off when the tank gets where I want it. Also, the button should work when the car is parked and/or driving.
 

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Fuel flow rate is very easy to accurately measure to a fraction of 1%. It probably would be easy enough to digitally show how much fuel you have used since your last re-fill. Digitally showing how much you have left, though, is a tougher cookie. Tanks are mass-produced and can vary by several % from the factory. Fuel pickup levels are not exact. Tanks and fuel both expand and contract with temperature, at different rates. Gas sloshes around in the tank and the level sensor moves up and down, depending on whether you're going up hill or downhill. Basically, tank level is always a moving target and an educated guess at best. That's why the manufacturers usually just use an analog display and set the "empty" level relatively conservatively. Your needle usually bottoms out when you have at least 10% left.

As far as weight is concerned, the Volt will have a 7 gallon tank. At less than 6 lb per gallon, keeping your tank at least half-full only adds 22 pounds to the weight. Other than the hyper-mileage fanatics, I can't picture anyone skimping on such an important item like adequate fuel just to save 0.5% in mileage. Besides, lots of bad things happen when you chronically run on empty or "drain the tank". You're sucking higher percentages of the water and other junk that collects in the bottom of the tank - not good for the engine. The GM service departments would have fits with a drain-the-tank feature. Keep it half- full and add a little gas stabilizer if it goes for months between fill-ups.
 

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I agree. Keeping the tank at least 1/2 to 3/4 full minimizes condensation and helps dilute impurities. The detergents in gasoline will also help keep the tank, and more importantly, the sending unit clean.

When I park my boat for the winter, I fill the tank about 1/2 full and use a stabilizer. Then in the spring I fill it full with premium higher octane fuel and it always runns great the first time we use it. Other people try different methods and usually need to "burn out a fresh tank" before the engine is running smooth.
 

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Discussion Starter #5 (Edited)
hvacman & Eric E, thanks for your information. So draining the tank probably is not such a good idea. I guess I'm still left with aging gasoline. I have read so many different opinions about the lifespan of gasoline in a hot climate (I live in South Florida) that I'm a bit concerned. I put fuel stabilizer in my generator (hurricane precaution) because I can easily estimate when I will use it next and I know how much because I can look in the tank.

With Volt I will not really be able to estimate the next trip I take nor the amout of fuel remaining wihout an accurate gauge. I don't want to experience burning "the bad stuff" or having to track (in my aging brain) when I last put gas in the car so I think "hummm... maybe a bit Stabil is called for since it has been N months".

That is what embedded processors, memory, sensors and software are all about, helping me with the things that I don't do well. I guess I could just resort to not charging and burning a tank every 3 months but that sort flies in the face of what the Volt is all about. Don't you think?
 

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I find it hard to believe that that problem can't be solved. Four sensors in the corners would allow you to calculate volume even if it's sloshing around. The temperature sensor will tell you how cold/hot it is and from that you can calculate expansion/contraction and how it will burn in the engine. To me it soulds like a math problem and a design problem. Both of which can be solved. I think it's time to make an advance in tank tech.
 

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Here is an interesting product: http://www.priproducts.com/

According to their website and faqs(http://www.priproducts.com/prigfaqs.htm) it can be used over and over again for years and will make even the oldest fuel usable and remove any "soft" carbon deposits from your engine components.

I've been using PRI-D (not to be confused with PRI-G) in my diesel engines on my boat for years. Fuel capacity is 750gal. using 2 tanks. Although I use the boat more locally and therefore don't use a lot of fuel, the last time I filled them, it cost $1.56gal. That's without the road tax. That was about 2 years ago and the boat always runs fine. I regularly check the fuel filters and water separators. I still have approx. half that fuel remaining.
 

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Not that I want to wish the fuel tank bladder issues of the Prius on anyone, but it seems to me that a bladder type system makes a lot of sense in the Volt. The issues we have with it on the Prius (variable capacity based upon temp, Some fuel gauge accuracy issues, some 'spit back' if you try to top up) would seem less important in the Volt since fill ups would be so rare and it would be infrequent that you'd be running the tank dry.
Also, the clear advantage are the exceptional control of evaporative emissions of the volatile gas. It would do a great job of helping preserve the gas for longer term storage/use...particularly with a little stabilizer added.

Final comment...several people have talked about just keeping 1 gallon of gas in the tank. That seems fine if you are regularly (every 3-6 months?) going to burn that gas off and add fresh. If you do not expect to use it then it actually makes more sense to keep the tank full. There's a lower fuel to air space ratio (unless using a bladder system) and thus less volatile emissions and chance for water condensation. It's always best to keep a tank full for long term storage.
 

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State of charge

The more interesting challenge is to measure the "state of charge" of the battery. How will the Volt do this? It has to do it some way to known when to turn on and off the ICE. Will it just measure battery voltage? (Fraught with hazard, for sure.) Will it measured "charge consumed" in some way? Other? Sure, the battery can be run to depletion, but then its too late. What comes before?
 

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One other comment about gauges. I think instrumentation engineers have learned that our human brains can more quickly interpret data presented in analog form than digital form. Control panels on everything from power plants, aircraft, to autos use more analog gauges/data displays (or digitally-created analog gauges) than digital displays. It's easier to scan an array of analog gauges and spot one where the needle or bar is a little low than to scan an array of numerical displays and figure out which one is below normal.
 
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