car MPG help required

Ukuser

I run a 52 plate astra 1.6 LPG

a full tank of lpg (58 litres) gives me approx 350 miles. This is mainly dual carriageway driving

(average cost of lpg is 77ppl)

I have just punched the above figures into the online MPG calculators and its coming back as 27.4MPG - this seems very low

I then looked online and found the official mpg figures for the same car in petrol version are 29/39/49 mpg - town/combined/motorway!

Could somebody please explain why im getting such low mpg or where im going wrong in the calculations

thanks

miq

victor2

Your calculation looks about right. Have never owned an LPG powered car, but don't they return lower mpg than petrol? The saving is in the cost of the fuel.

clever_username

Why do people say "I run a Vauxhall Astra" instead of "I drive a Vauxhall Astra"?

Off the top of my head does a car using LPG generally achieve the same fuel economy figures as its petrol equivalent?

Style of driving is massively important obviously, you mention 'dual-carriageway driving' but blasting along that dual-carriageway at 90mph for example would lead to low MPG. Not that I'm accusing you of speeding you understand but merely illustrating the difference that driving style would make.

Ukuser

thanks for the quick replies.

is 350 miles from £45 a good/average or bad figure?

i thought i was doing great guns using lpg but the figures dont look that good.

as i said most of my driving is dual carriage way at 50/60 miles and hours.

regards

miq

clever_username

To be honest the whole attraction of LPG isn't that it gives more MPG but rather than it costs less to buy per litre than petrol.

So whereas it costs the owner of a petrol car £1.40ish to buy a litre of petrol to travel lets say ten miles, it only costs the owner of an LPG car 80ish pence to travel that same distance if you follow me.

I honestly wouldn't get too hung up on the economy. As far as the car's MPG goes it just does what it does.

FATBALLZ

Ukuser wrote: »

thanks for the quick replies.

is 350 miles from £45 a good/average or bad figure?

i thought i was doing great guns using lpg but the figures dont look that good.

as i said most of my driving is dual carriage way at 50/60 miles and hours.

regards

miq

I drive a 1.6 petrol car that costs me slightly less in fuel, I get about 50mpg. Although I do drive as fuel efficiently as I can.

jaydeeuk1

Always thought LPG did about 2/3 the MPG as petrol, but at half the cost, so figures look about right.

In the majority of times, very few people get close to the quoted MPG for a car, so wouldn't pay too much attention to the 29/39/49 figures

sujman

Ukuser wrote: »

thanks for the quick replies.

is 350 miles from £45 a good/average or bad figure?

i thought i was doing great guns using lpg but the figures dont look that good.

as i said most of my driving is dual carriage way at 50/60 miles and hours.

regards

miq

According to my calculations, £45 for 350 miles comes to about 12.86 pence per mile.

With the current price of petrol in my area being 132.9 pence per litre, I would need a car that achieved at least 47 MPG, for the cost per mile to be the same as yours.

My current car (54 plate ford focus automatic) gets at best 38 MPG, which is 15.90 pence per mile.

Automatics are nutorious for being very poor efficiency, so I would hazard a guess that a regular, well chosen car could achieve 47 MPG.

If thats the case, then I personally would not bother getting an LPG car, as the savings do not seems hugely significant and also due to the lack of suitable stations in my area and potentially any other additional costs that, that type of car could incurr - admitedly, I dont know of any but I am not an expert!

Kilty_2

Is it a 1.6 8v? They're crap on fuel in petrol guise never mind LPG

asbokid

From Honest John...

"There is now a standard conversion of the Perkins 180 diesel engine for buses and trucks, enabling them to run on LPG at the increased consumption rate of 25 to 50 per cent, but using a fuel which is less than half the price of diesel.

Not any more! LPG costs ~78p a litre. That's 60% of the price of diesel. Conversion of the Perkins diesel to run on LPG is not prudent.

Usually a petrol engined car running on LPG suffers a 10% to 20% increase in fuel consumption. If it uses more LPG in comparison to petrol the reason might be the siting of a crucial part of the conversion, or it may be that the fuel stations are short changing the amount of LPG they supply.

http://www.honestjohn.co.uk/faq/lpg-and-cng/

santer_2

Ukuser wrote: »

I then looked online and found the official mpg figures for the same car in petrol version are 29/39/49 mpg - town/combined/motorway!

The accepted use of LPG is 20% more than petrol, so you should look for 23/31/39 approx

Conoco Phillips - Fuel Supplier

One important environmental caveat with LPG is that it actually uses up to 20% more fuel by volume than petrol.

http://www.post-carbon-living.com/Substitute_LPG_Car.htm

http://www.fuelture.com/option,com_lpgcalculator/Itemid,108/

Has the LPG system been serviced?