Quote:
Originally posted by Christian@Apr 8th 2004 @ 10:07 AM
I talked with the mechanic at the Toyota dealer here when I was taking my 2004 prius in for another problem (which I will talk about elsewhere) about the gas gage issue.
I had two bars of gas in there and he told me to fill up the tank. I responded that the there was still a lot of fuel in there and he said I should fill it up when there are two bars as the computer will think that the car is running out of gas and can give error codes. I'm not really sure if this is really the case but it does say in the manual (p. 114) "it is a good idea" to not let the tank level fall below 1/4 of a tank. No real explanation of why this is the case, however.
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Welcome, Christian
I feel this is a combined case of "not really knowing/thinking about what they are saying" and maybe some old-car mentality.
As I have stated elsewhere (either in this post or somewhere else, not sure), the "1/4 full needs gas" scenario is based on either one or both of two thought processes - the most prevalant (I feel) is the cooling of the in-tank fuel pump.I do not accept this as valid for two reasons:
1: fuel in the line is adequate to cool the pump if needed
2: I have several vehicles well over 200k miles that are habitually run to fumes - I have NEVER replaced an in-tank fuelpump before 150k miles - which is WELL over their rated time, prooving, for me, point 1 above.
The second reason is actually more "real' - but doesn't really apply either - water in the tank. When you have space above the fuel in the tank, that space is filled with normal air - containing moisture, sometimes lots of it. As you may be aware, water will condense from the air on the sides of the tank and pool in the bottom in wells designed for the purpose - at least, they WERE desigend that way long ago - the newer plastic tanks may, in fact, not have any need to catch and try to contain water in the fuel.
In any event, there is supposed to be NO space above the fuel in the Prius - the fuel is in a "bladder" that basically surrounds (should surround?) the gas entirely. It may be partially responsible for why we can't really get 11.9 gals into the tank when we feel it is empty - but in any event, it "protects" the fuel from EXTERRIOR moisture that one would get from tank condensation. (It will NOT prevent water from entering the fuel in opther ways!)
In any event, small amounts of water are normally taken with no problems by the engine - large quantites are of course more of an issue.
But - his "suggestion" - and reference in the book - really suffer from a new deficiency - even if you decide either or both (or other) reasons above are good ideas to follow - at two bars, the tank is half full, not 1/4 full!
The tank holds (or is RUMOURED to hold!) 11.9 gallons. Most people feel it holds somewhat less - so let us just say it holds 11 gallons bone-dry to full.
Most folks I have heard from (myself included) report that if they fill AS SOON AS POSSIBLE after the flashing of the gas guage lights - they can put in maybe as much as 8 gallons - 8/11 is pretty close to 3/4 (~0.73 vs 0.75) - so the tank is just about 1/4 full when the last bar starts flashing. It is my sense that the difference between two bars and a flashing last bar may be 50-80 miles which may be as much as two gallons (depending) - putting the tank at maybe 6 gallons of fuel gone at two bars - almost half full!
Or over half-empty, depending on the kind of person you are.... ;-)
I can et about 120+ miles out of my tank when the flashing starts - to me, that is 2.5 gallons of fuel remaining or ~7.5 galls gone when flashing starts. I set the B odo and watch it - even carry a spare gallon (50 miles!) - A PRACTICE I DO NOT ADVISE! - of fuel. I have run out once (only the second tank!) and don't have as perfect a set of records on that to really get reasonable data, but I plan to "run it dry" a few more times for Science.
I am not at ALL worried about the pump. I am MUCH more concerned with those that "overfill" the tank thinking they are going to get good results. There is too great a chance of inadvertently (and unknowingly) damaging the fuel vapour system with overfilling.
Jack
