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I have a 2006 Harrier with the 4-cylinder engine. Today I did 86 miles and tracked the mileage with fuelly which showed 23.5mpg. This was a combination of urban driving, cruising at 50 through the average zones on the M23 and cruising at 83 for most of the rest of the motorway. All together should be a fairly good average of the kind of driving I tend to do.

So on petrol at £1.28/L 23.5mpg gives 0.258p/mile

LPG would be a 20% efficiency loss (could be less but lets assume 20%) so I should see around 18.8mpg, and at £0.62/L that works out to 0.15p/mile.

I do about 9000 miles/year so on petrol 9000 x 0.258 = £2322. On LPG 9000 0.15 = £1350.

I was quoted £1275 to convert the car by a local specialist. For a saving of £1000/year on fuel (as a conservative estimate) this seems like a no-brainer.

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Absolutely a no-brainer! I've never understood why more people don't do it.

We haven't got our RX300 anymore but when we did, I used fuelly and found that a standard petrol-only RX300 was running at 22.5p per mile, an RX400h was 19.6ppm and our LPG RX300 was coming in at 12.6p per mile!

A European driving holiday saw us go from Preston, Lancashire, through France, Belgium, Germany, Czech Republic and Poland. Petrol would have cost us over £900 at the time but doing it on gas cost us about £440-£460ish if I remember right.

I'd love to go back to LPG but while it can be done on a hybrid, I really don't think it's a good idea to introduce a whole new layer of complexity to what is already a very complex car.

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Turns out my math was off because I had the mobile app set to US MPG rather than UK MPG.

petrol - 28.2mpg - £1.28/L - £0.206/mile
LPG - 22.56mpg - £0.62/L - £0.125/mile

9000 miles on petrol - £1854
9000 miles on LPG - £1125

range on petrol 72L - 446 miles
range on LPG 70L - 347 miles

adjusted mpg on LPG: 46.58 <-- this is nuts, that's diesel economy!

So actually more like 20 months to get ROI assuming this average is representative.

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Just be very careful to get someone who actually knows what they're doing and who has a great reputation. For instance, don't let anyone near it who would do an installation like in the first two pictures below.

Although they may look tidy enough in their own right, there's just no need for doing something like that, cutting the valve cover and having the injectors and pipework out on show. The last picture below is my RX300 and the numbered items are:

1. The Flashlube bottle
2. The LPG ECU
3. The LPG Reducer


badgas1.jpg.8a69383518bb15adc864d3ef87f20cfd.jpg

 

badgas2.thumb.jpg.7c1a4f3374e4464e5d4e934a5af9dd04.jpg

 

gascon.thumb.jpg.03b9ab86e45678af79b2be52a5877358.jpg


Oh, and I know I'm sad but I just have to say - it's 'mathS' not 'math' That's an Americanism that really grinds my gears!  :laughing:

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@Herbie How much fuel economy did you lose on average and how much fuel did you get into the 85L tank on average?

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Also sorry about the americanism 🙂 those things bug me too, I didn't realise that was one of them.

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The 85L tank capacity refers to water volume. The tank and gear are designed to have an expansion space for gas (I seem to remember about 20% but may be wrong). Anyway, in reality, the most I ever got in was 74.63L.

Below are the figures from Fuelly - you'll soon know which is mine  :laughing:

fuelly2.thumb.jpg.96542375bb444312a6d2b02aec252b41.jpg


fuel400h.thumb.jpg.eee262535efd14268f802c45af50bc31.jpg


fuelly1.thumb.jpg.0d1379eeaa5295efc30019f44cc5a683.jpg

 

 

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@Herbie I'm obviously missing a joke here because I have no idea which one of those is yours!  I guess what I wanted to know is the mpg drop you saw from petrol to LPG. Supposedly it's 10-20% but I'd like to get some real-world numbers.

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Oh is it the first one where it dropped from 27.5 to 22.6?

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1 hour ago, m4rkw said:

 I'm obviously missing a joke here because I have no idea which one of those is yours!

look at the price per litre

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Ah of course! So it's the last one, so what was your average on petrol?

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@Herbie I'm obviously missing a joke here because I have no idea which one of those is yours!


Sorry Mark, I should have pointed it out - but in my defence, I did say (in the second post down) that:

Quote

 found that a standard petrol-only RX300 was running at 22.5p per mile, an RX400h was 19.6ppm and our LPG RX300 was coming in at 12.6p per mile!

so I thought you'd just pick it up from the price per mile figure, sorry.

As for petrol consumption, on a motorway run I think we could get up to about 28mpg, but my average was about 22mpg (lot of town driving).if I remember correctly - we traded it in about 15 months ago and I've had a lot of beer since then so my memory isn't the best :laughing:

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Hmm, if your average went from 22mpg down to 16.2 that’s a loss of over 27%!

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2 hours ago, m4rkw said:

Hmm, if your average went from 22mpg down to 16.2 that’s a loss of over 27%!

Check again as I make it 26.36363636 !!  (lol)

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Still too high though. 20% is banded around as the "average" and I've seen people reporting far less. I'm trying to work out the ROI period but it's hard getting accurate numbers.

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I am not against LPG conversion, but recently reading about this on an honestjohn forum, and you also need to factor in extra mileage to get to somewhere that sells lpg. I looked into this but don’t do enough miles to warrant, plus something extra to go wrong, and extra service cost. I also am conscious that any minor accident and the insurance company will write the car off, at its market value. There are many on here delighted to have converted, and saved a lot of money, so you pays your money and takes your choice. Good luck whatever you decide, Roger

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34 minutes ago, m4rkw said:

I'm trying to work out the ROI period but it's hard getting accurate numbers.

That's because people drive differently and mine isn't exactly a great example because I do a lot of town driving with a lot of stop/start journeys. Also, because I'm self-employed I can be in and out of the house three or four times a day for work, but the timings always seem to be such that the engine is cold, so more fuel used there, plus I may well be out with my figures - I did say it's been a long time since a) we had the car, and b) since I actually took notice.

My advice? Don't get bogged down in figures - just enjoy the fact that my European road trip cost half of what it would have done on petrol; enjoy the fact that in the examples above from fuelly, I only spent £817 to get much further than those other guys who spent over £1,100; enjoy the fact that every time you fill up you'll have a big grin on your face - especially if there's a petrol shortage :laughing:

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@Herbie how much petrol did you get through in a month while driving on LPG?

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So from talking to a friend and from online sources it seems like you're supposed to run 20L of petrol through the engine every month, if for no other reason than ensuring the petrol in the tank is fresh. This puts a serious dent in the economics of the conversion, pushing my ROI out to 22 months (based on an assumed efficiency loss of 10%) and an annual saving of only £546. The local installer estimated 7-10% loss but said it could be higher depending on the engine. If it was closer to 20% that would push my ROI out to 27 months and bring the yearly savings down to £410.

If i did more mileage obviously this would change dramatically but given the hassle involved in using gas I'm starting to think it's not worth it.

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2 hours ago, m4rkw said:

So from talking to a friend and from online sources it seems like you're supposed to run 20L of petrol through the engine every month if for no other reason than ensuring the petrol in the tank is fresh.

Absolute rubbish!

The car starts on petrol every time and then will seamlessly change over to gas when certain parameters have been met, the main one being coolant temperature. I seem to remember mine being set to 35oC, or to put it another way, 2 or 3 minutes or half a mile to a mile. This is so that the LPG reducer can easily turn the LPG from liquid to gaseous state to deliver to the injectors.

So yes, you do use petrol as well as gas but absolutely nowhere near 20L a month and you don't need to "keep the petrol fresh" - and while I don't claim to be an expert, I have driven more than 220,000 miles on gas so I do know a bit about it.

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@Herbie How much petrol were you getting through?

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Just now, m4rkw said:

@Herbie How much petrol were you getting through?

I truthfully can't remember now because as I said, it's been a while. What I can say though is that I filled up with petrol in Poland because it was ridiculously cheap, and I was still using that Polish petrol months later.

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Petrol degrades over time so the general advice seems to be to keep a small amount in the tank, say 1/4 maybe, and top it up as it gets low so that you've always got relatively fresh stuff in there.

In any case, even if I assume only 5L/month of petrol, the economics still don't really come out in my favour as I'm only doing about 9000 miles/year.

2 years to break-even and then only a £500/year saving isn't really worth the hassle imo. If I was doing a lot more miles it'd make a lot more sense.

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Fair enough, it definitely isn't for everybody but we loved it and it saved us a hell of a lot of money. I could never afford to run the RX300 on petrol but LPG enabled me to have the comfort and luxury of a great car at a very reasonable fuel cost.

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I'm seeing 27.8mpg on mine just on petrol, and that's driving it pretty hard. I could probably get that up quite a bit on a long run.

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