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Old 06-30-2011, 09:58 AM   #1
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Join Date: May 2011
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Country: United Kingdom
LPG or twin tank systems...

I run an LPG (propane) system. How does Fuelly cope with a twin tank set up?

Well, Fuelly seems to cope quite well! In the UK Propane is half the price of Petrol (gasoline) but your engine burns more of it (about 20%). So what I want from fuelly is a cost per mile figure that allows me to compare to other vehicles, rather than focusing on MPG which will give the wrong picture totally.

Now any car with an LPG system will burn normal petrol. It is required to warm the engine before switching over to propane and if you run out, the system reverts back to petrol. So, despite the limited use, I need to know the usage of both fuels to fully understand what my vehicle is costing.

What is the best way of doing this? Currently I have been recording every full up, but I tend to fill both tanks at once when the petrol gets low. this means I input 2 fuel ups on the same odometer reading with different price per litre. I have found that I input the propane first then the petrol, it seems to disregard the 0mpg of the petrol fill from the average mpg, yet still contributes to the overall cost. This it what I am interested in knowing, but is there a better way I could be doing this?

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Old 06-30-2011, 11:39 PM   #2
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Join Date: Oct 2009
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If I was doing this, I would probably approach it this way, same as I would with a truck that had 2 gas tanks, like some of the older 70 something chevy trucks.

Fill both tanks.

Add the total volumes together. (IE: total gallons of both tank fill ups)

In your case, add the total cost of each tank together and divide that by the total number of gallons, etc to get a price per gallon for all the fuel together.

Then enter your trip or odometer and the above results. That way each fill up would give you a representation of total cost/total fuel gallons, etc.


You filled up your petrol tank with 10 gallons at 6 per gallon so its 60 for a total.

You filled up your LPG with 10 gallons at 3 per gallon so that's 30.

So you add 10 + 10, giving you 20 for gallons; Add 60 and 30 which gives you 90 for your total fill up cost. 90 divided by 20 gallons gives you a price per of 4.50.

Then you just enter your mileage/trip, the total gallons (20) and your price per gallon (4.50). Bit of math but not that bad.

I don't think Fuelly is setup to allow break downs on a per tank basis beyond one tank per fill up. So while this may not be quite what you are after, it will at least show you what your mileage is using the mixture of both tanks.

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Old 07-01-2011, 11:39 AM   #3
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Join Date: May 2011
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That's a good idea, though I only fill both tanks roughly evey 5 fill as petrol is used so sparingly. I may try and Chang my last double fill retrospectively to see what a difference it makes to the figures.


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Old 08-11-2011, 10:28 AM   #4
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Country: United Kingdom
Location: Norwich
John have a look at what I'm doing with my Stilo. I track all LPG fill ups on one log, and record price for the petrol on another. I always brim the fuel tank between Christmas and new year so it's always full going into a new year, and then used the total £ for the year spent on petrol, and it to the total spent on LPG and decide my the mileage clocked. Tbh the amount of petrol used in summer months is minimal (I'll use 1/3 of a tank between may-sept) so the cost per mile is fairly accurate in the summer months.

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