LPG Discussion Forum

I went through a stage of filling up my LPG tank at half a tank (I always fill to full), say when passing a LPG station, so I never ran out.

I then noticed that by doing this I was getting a lower MPG return than when leaving fill-up until reserve light was flashing.

Obviously when filling, when removing filler pipe you get a gas discharge, so if filling twice with 2 half tanks rather than once with a full tank, one was loosing gas twice.

Question is, has anyone else noticed this? And does anyone know roughly how much gas is lost everytime the filler pipe is disconnected?

Jon.

the tinyiest dribble. Afaik the gas expands approx 250 times when expanded top atmospheric pressure

For what ever reason topping up from about half tank or above seems to give more consistant MPG figures.

The MPG when you fill to the top from a near empty tank appears to vary much more but if take average over several fill ups it turns out the same.

For the last couple of weeks I have been topping up after 100miles --- it always costs me less than a tenner a fairly consistant 9.7p per mile at 51.9p per litre --- a Rover 75 that cost less in fuel than a Toyota Prius or Smart Car which makes me one happy meerkat

I find you can only get a really accurate MPG from one fill up to another if using the same pump all the time as I'm sure the cut off on some are more premature than on others.

You won't get any reliable figures if you are running xxxmiles then filling up and expecting the cut off to always be at the same point. pump to pump it will be different even the same pump at different times will vary the cut off point. The pump I fill up at will sometimes give me 37 litres on an completely empty tank, and sometimes 44 litres from a completely empty tank.

The only way to be sure is to run completely empty, go to the pump on petrol (I know it's expensive ) fill up say 40 litres and the run xxxmiles until completely empty again. Now you know 40 litres took you xxx miles exactly no messing no arguments no unknown variables (apart from the variable traffic and foot/pedal conditions)

As already said, filling is inconsistant due the increased variables with LPG over petrol. I've even noticed that I seem to get more in the tank on a cold day compared to a hot day!

himselfunknown wrote:As already said, filling is inconsistant due the increased variables with LPG over petrol. I've even noticed that I seem to get more in the tank on a cold day compared to a hot day!

lol, well thats slightly obious happens with all fuels - basic physics