Thursday, 31 January 2013

Should I Convert My Car to LPG?

I like cars.

I like fast cars, but with a new family and a restricted budget, I don't really have the funds for it.

Or do I? I've been eyeing LPG conversions and apparently, a car running on LPG is only slightly less powerful, and will give slightly less mileage, (I'm led to believe it's about a 10-12% loss).

But have you seen how cheap LPG fuel is??

Let's do the maths...

As of today's date, average fuel prices per litre across England are as follows:
Petrol (Gas)  £1.32
Diesel           £1.39
LPG              £0.75
OK, you Americans at the back, you can stop laughing now please ;)

So far so good, if you already have a converted car, running on LPG, clearly it's a no brainer. Fuel is 57% of the cost and mileage, at the worst, 12% less.

But firstly, what about diesel? Modern diesels are just as powerful as their petrol powered brethren these days, so should we even bother with LPG? Well let's get that out of the way then.

Diesel cars are said to be about 40-45% more fuel efficient than petrol powered ones, so I quickly checked Autotrader to see. I looked at Renault Lagunas, partly because I have one, and partly because the french make very good diesel engines. Here are the results: 
2006 1.8 16v petrol with 122bhp - combined figure 37.7mpg
2006 1.9 dCi diesel with 120bhp - combined figure 51.3 mpg
I picked the combined figure as it's realistically achievable with a gentle right foot

Average mileage in the UK is around 15,000 miles a year, so taking the 2 cars above, the petrol one would cost you £2387 in fuel each year, and the diesel would be £1847 a year. You're 29% better off with the diesel but you still have the same performance, (the cars have almost identical power and acceleration figures).

So back to the LPG.

Doing the maths again, (using the worst 12% loss figure), the petrol laguna converted to LPG would return 33.2 mpg and cost £1540 over 15,000 miles. So yes, fuel cost wise, the LPG wins but at a 10% power loss. If you want to make up the power loss, we'd have to start with a 2006 2.0 16v petrol laguna which has 135 bhp and does 35.3mpg. An LPG conversion would bring those figures down to 123 bhp and 31 mpg. The fuel cost would be a bit more at £1649, so there's quite a bit of margin still over the diesel, meaning you could probably stretch to a much more powerful car :)

So let's have a look at power then.

You can get a laguna with a 3.0 V6. I've had one - very comfy, all the gadgets, 210 bhp so quite quick, and despite the huge lump in the nose, handled quite well, BUT. It certainly liked a drink, and in day to day driving I never saw more than 28 mpg, (Renault quote 28.5 for a 2006, mine was a '99).

So the figures then. LPG mpg would be 25 and the fuel cost over 15,000 miles would be £2038 (although if you only lost 10% mpg it would be £1993).

So not as good as the 1.9 diesel, but still far better than the 1.8 petrol. There's also the 2.0 turbo with 170 bhp. That comes out at £1832 with LPG.

What about other costs though, like paying for the conversion in the first place?

Well, a quick google search reveals that a 4 pot motor will be around the £750 mark, whilst 6 cylinder engines are abviously a bit more at around £1,000. Certainly, if you just want to save money, then yes, it looks like LPG is a winner here, and with an average annual mileage and an ordinary 1.8 motor, you'd actually be up on the deal inside 12 months.

If you plumbed for the V6 though, it would of course take longer to pay for itself, as you're only saving about £300 a year, BUT, the V6 can counter in other ways. Take initial purchase price - the older a more performance orientated car gets, the more it's price depreciates compared with it's more lowly siblings, and there are several reasons for this:

Firstly, those of us who can afford to buy these types of cars when they are newer, tend to lose interest in them over time, when they get on a bit and newer, more interesting cars come on the market. Secondly, these sort of cars do have higher servicing costs, and as a car depreciates, this starts to become a much bigger consideration for buyers with less money to spend.

So basically, a car like this needn't be much more than the more basic models to purchase. However, for the very same reasons, it makes an LPG converted model more valuable come resale time. People want a nice car, and if the running costs are lower, they'll pay a premium for this. In other words, you get some of your money back :)

So in answer to the original question, "Should I Convert My Car to LPG?", it does look like a good deal regardless of the car you plumb for, and it's also a good way to keep the costs of performance motoring down.

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