So trying to heed the advice I recently read here about filling up in the morning ,because you don't get hot gas, I went this morning to fill up my tank. I get to the station and its the coldest night last night yet this summer (40 degrees). My MFD reads 46.4 MPG which is one of my worst tanks yet due to sitting in lots of traffic lately. I had gone 420 miles on this tank and was down to one bar on my display. So I was surprised when the pump shut off at 6.82 gallons. A quick calculation makes gives the previous tank a mpg of 61.7. I know the issues with the MFD vs hand calculations but before i was averaging a difference of .79%. This tank was a difference of 24%! My question is: Is this a case of a bad pump or really cold temperatures shrinking my bladder the night before?
Maybe both. Bad (sensitive) pump and shrunken bladder (I'm assuming you are talking about the one in the car :lol: ) What is really annoying is when the pump doesn't automatically shutoff. I have had that happen two times now in 10k miles.
<div class='quotetop'>QUOTE(dogfriend @ Sep 17 2007, 04:18 PM) [snapback]513874[/snapback]</div> I wonder if the bladder not only shrinks, which would make a minimal difference,, but gets stiff. So when you are filling it, there is a dent or depression, or one side squashed, that does not expand when cold, thus decreasing the volume available for fuel. We need someone with an ultrasound machine to scan a few tanks.
It's been established - pretty much through anecdotal information - that you will usually get less fuel in a cold bladder. Yeah, Doc, the ruling speculation is that the bladder does get stiffer.
<div class='quotetop'>QUOTE(TonyPSchaefer @ Sep 17 2007, 05:45 PM) [snapback]513912[/snapback]</div> update: So Afterwork I went back to another gas station and filled up 2.4 more gallons. Temperature had only increased to 63 degrees but i guess thats probably enough. And a better pump <div class='quotetop'>QUOTE(dogfriend @ Sep 17 2007, 04:18 PM) [snapback]513874[/snapback]</div> wow I can only imagine I dont look forward to that experience
<div class='quotetop'>QUOTE(SureValla @ Sep 17 2007, 01:48 PM) [snapback]513832[/snapback]</div> 40F is no where near cold enough for the bladder to enter the equation. Try 20F for starts. Near 0F becomes obvious. You probably came across a pump with an olded sensor. They do eventually need to be replaced.
I really can't see the temperature of the fuel stored in an underground tank changing all that much due to variations in atmospheric temperature through a day. Those tanks are pretty huge so would require a huge amount of energy to change the temperature much and being buried the soil or sand they are in would insulate the tanks from daily fluctuations. I have heard complaints about oil companies shipping hot fuel which stays hot in storage reducing the density of the fuel when it is pumped into your car but not about daily fluctuations. In Coober Pedy people live in "dug outs" or underground housing because the temperature in a dug out is stable at about 24c while the outside air temperature fluctuates between 50c and -7c day to night in summer. I googled and found this. http://www.turndownhotfuel.com/myths.html an interesting read.
<div class='quotetop'>QUOTE(patsparks @ Sep 17 2007, 09:33 PM) [snapback]514039[/snapback]</div> wow very good point Im ashamed I didnt think of that So trying to fuel up in the morning only is beneficial if the truck was also delivered in the morning when the fuel would be a lower temperature going into the ground. I would enjoy seeing the chart at the bottom of that page showing the millage on temperatures down to 0 degrees.
The temperature of the fuel coming out of the storage facility will have more affect on the temperature of the fuel than the air temperature. Again the tankers are really big so would require a long time to alter the temperature much. Most major cities have bulk fuel storage so the journey to the petrol station wouldn't be very significant. If fuel comes from a refinery directly to the petrol station via a truck and is not stored for a very long time the fuel may be much hotter because refining petrol uses heat, lots of it so refinery fuel is hotter. When fuel is pumped from oil company storage and sold to petrol stations the density is calculated and corrected so the price the reseller pays is for the mass rather than the volume of fuel. That's a point, why don't we buy fuel by the pound of kilogram? Problem solved.
I'm guessing the bladder causes a little more back pressure than a regular tank and some pumps react badly to that. If you have been calculating your actual miles and gallons pumped in, you should have a good idea of the accuracy of your MFD numbers. Mine runs about 2% higher than actual. With that info, I know that if my MFD says 51 MPG and I've driven 500 miles, I can put in a minimum of 10 gallons. If the pump shuts off before my calculated amount, I pull the nozzle out enough to avoid the auto stop and pump slowly. The only time I would worry about this is if I were to fill it then immediately park it in the hot sun for hours.
<div class='quotetop'>QUOTE(SureValla @ Sep 17 2007, 02:48 PM) [snapback]513832[/snapback]</div> I went on a long trip and had stopped at a station and I knew I should be putting in about 7 gallons, but it stopped at just under 5 gallons. I too thought wow, that's great. all the bars came on. I went in to use the rest rooms, came out, started the car and one bars were off. went to a different pump and took 2 more gallons. My conclusion is that it was the pump, because I tried over and over again at the first pump to add more and it just kept turning off. Richard
<div class='quotetop'>QUOTE(richard123 @ Sep 19 2007, 01:48 PM) [snapback]514897[/snapback]</div> I have to wonder in a case like this if the fuel hasn't had a chance to 'weigh' on the flexible bladder and cause it to stretch a bit, thus allowng more fuel to come in.
I do not know about weights or temps or nuthin'. I just know that when the automatic shutoff happens, I still have at the very least one more gallon to go to fill up my tank bladder. I probably spend WAY too much time clicking and filling to bypass the automatic shutoff that keeps hitting back. It takes a lot longer, but my tank is full. I only VERY rarely overfill at this point (27k miles on the odo)--I can mostly hear when it's full, or, with many pumps, since I have to take out the nozzle for each nudge, I can see it. It's just my exciting life. What can I say?
<div class='quotetop'>QUOTE(john1701a @ Sep 17 2007, 09:17 PM) [snapback]514029[/snapback]</div> I also had trouble filling the tank one time and the ironic thing is that it was approximately 40F.
