How can I record Bi-Fuel (Petrol + LPG)?
 

I am due to receive my new Dacia Duster Bi-Fuel in the next 2 weeks and couldn’t figure out how best to record my data.

This car has a 50 litre petrol tank and a 34 litre LPG tank. I’m not sure I want to fill both tanks fully each fill up as both full tanks weigh around 100lbs together which I’m guessing would impact MPG as additional weight?

The only way I can think to record this though would be to fill both tanks each time I fill up, add litres together add total cost together and record as one transaction?

Any other ideas or information regarding the impact of 2 full tanks on MPG would be greatly appreciated.

Can you decide which fuel the car uses? Or does the car switch between the two automatically? You could fill and use one tank at a time and have a separate profile for each, Duster petrol, Duster LPG. If you had two trip meters like many cars do, you could use one for each tank to record the miles driven on each fuel. This way, you could see the MPG differences and cost comparisons as you wouldn't be mixing the two together. Just an idea, don't know how practical that would be or if it would even work.

Wow, that’s a really good idea! I can manually switch between tanks and yes it has 2 separate trip counters!

I love this idea of being able to see mileage separately, thank you!

EDIT:

On second thought I would need to keep individual track of each journey made so may be a bit of a pain unless I can find some way of auto tracking journeys on my phone or something that I can label as LPG / Petrol to help determine.

Are you using trip meter tracking or odometer tracking? If you have trip A and trip B in your new car, which most cars do, you could use one for each fuel and reset each one for each time you fuel up?

I thought fuelly only allowed odometer tracking?

Also, my current car has trap A and trip B but they both keep counting miles together. So if this happened on my new car and I filled both tanks from 0 to max then did 200mi and reset trip B for LPG then did another 400mi then reset trip A for Petrol then did the same again I would have 1200mi on the odometer but I’m guessing my MPG would be all wrong as my petrol would think it did 600mi but 200mi of that was LPG (hope this makes sense).

Would I need to just strictly use one fuel until next fill up and cannot mix usage? Also is the trip A and B I am used to completely different to what you was suggesting?

You can switch your method of tracking via the vehicle profile. I prefer trip meter tracking myself as it doesn't matter if you miss a fuel up or ten fuel ups. You just reset it at the start of every full tank and off you go. But yea, most cars now have two trip meters, often called A and B or 1 and 2. But I guess the afore mentioned method I suggested would require you to run solely on one fuel, unless if you did switch fuels, you'd have to take note of trip A or B when you did it, then reset it again when you switched back. Could get very confusing and annoying and would only add stress to your journey.

I guess you could just have one mixed account, use both fuels, fill up together and put the total as one fuel up. That's assuming LPG is delivered in litres, and of course you'd then have to add the cost per litre of each fuel and divide by two to put an average in. Your fuel up would then display your average cost and MPG, again a bit confusing, but if tracking cost is more important, it could in theory work. I'm probably overcomplicating this, maths was never my strongest subject...

Here's how I would do it.
Use two profiles with trip meter tracking. Use trip A for petrol; only reset it when the tank is filled. Whenever you switch to LPG, reset trip B. When you switch back to petrol, make a note of the trip B miles(low tech would be a Post It pad in reach).

For a petrol entry, use the trip A reading minus the recorded LPG miles during that petrol tank. For a LPG fill, just those entries up. More work, but you are only tracking one manually.

Of course, you could luck out. Many hybrids track an EV ratio. Maybe your car can track each tank separately, or something like a Scangauge can do it.

The real problem is Fuelly is not designed for bi-fuel vehicles, whether LPG or electricity.
Accurately recording bi-fuel usage really comes down to paper and pencil (recording when you swap from one fuel to another), and a spreadsheet of some sort.

I think this may be the best thing to do, I’ll keep a notepad in the car and maybe just make a odometer note and when filling or switching fuel.

So my list would be something like with X meaning this fuel now active:
| Odometer | Petrol | LPG _ |
| 0 _______ | refill __ | refill X |
| 220 _____ | X ____ | ______ |
| 300 _____ | ______ | refill X |
| 520 _____ | X ____ | ______ |
| 600 _____ | ______ | refill X |
| 820 _____ | X ____ | ______ |
| 900 _____ | ______ | refill X |
| 1120 ____ | X ____ | ______ |
| 1200 ____ | ______ | refill X |
| 1420 ____ | X ____ | ______ |
| 1500 ____ | refill _ | refill X |

Then I can record LPG as trip on Fuelly on a LPG profile so the second fill would be 0.57 cost per L for 34L over 220mi giving 35 UK MPG (29 US MPG).

And I can record Petrol as trip on Fuelly on a Petrol profile so the second fill would be 1.33 cost per L for 50L over 480mi giving 44 UK MPG (36 US MPG).


The above calculations are the figures I’m expecting to pay/achieve but only time will tell.

The list won’t be as rounded as that but should be fairly easy to complete and transfer as trip data to Fuelly with some simple calculations.

I’ve just done a bit of testing in the app and I think I might just use 1 profile and class all LPG refuels as ‘partial refuels’ then when I top of both tanks class that as a full refill to get an average MPG across both tanks.

You can see on the attached image how it should all workout on separate profiles and combined on the top one. As I’ll be using more LPG than Petrol it should favour the lower LPG MPG but also the lower cost as well and saves me keeping not of every switch over.

Thanks for the suggestions and advice everyone!