LPG, myth buster as I run it on my C240...

[grober]

One interesting factor would be that, most if not all? LPG cars have to start from cold on petrol. As we all know MPG figures for such situations are horrendous when running a conventional petrol car.
1. from the obvious one ---if the engine is running and the car is stationary then your miles per gallon is zero
but also
2. during the engine warm up the fuel air ratio is very rich-idle speed is increased-engine and transmission oils are more viscous-auto gear selection to higher gears is delayed. typical figures are of the order of 5-10mpg for the first couple of miles
You would have to factor in this brief high petrol usage into your LPG figures somehow. At present presumably this remains "invisible" while looking at LPG mileage perhaps only to surface when filling up with petrol when it may erroneously become part of the petrol MPG equation?
I'm glad you are enjoying the benefits of running on LPG --all evidence points to it being a cleaner fuel for emissions but true straight comparisons can be skewed if every factor isn't taken into account.

Putting another way starting from cold on petrol--- fuel consumption is very high for a short time for both LPG and petrol. The danger in comparison is that that abnormally high consumption is being factored into the petrol MPG but not the LPG and worse case scenario in a comparison between fuels on the same car the cold start petrol use for LPG is inadvertently being added to the the consumption figures for running on petrol!

Crucial to any significance would be the period the car has to run on petrol from cold before switching to LPG. So-how long after a cold start on a winter day does it take before you can switch from petrol to LPG for example? Genuine questionas I have no idea.

 

[anglaslt]

Just after the collapse of MG-Rover I bought an almost new Rover 75 2.5 V6 that had been converted to run on liquefied natural gas (LNG). It was a LHD MG-R experimental vehicle converted by a company in the Midlands (Green Conversions seems to ring a bell). LNG sounded a good idea but availability of recharging points was an issue and, in any event, I bought it to take abroad so had it converted quite easily to run on LPG. The LNG tank was incredibly robust and heavy compared to the replacement LPG tank.

The car ran faultlessly for the two years I owned it and it still runs fine today according to the friend who bought it. Certainly LPG cars are economical to run if the conversion costs are excluded. My experience was a marginal increase in fuel consumption but I noticed no difference in performance. I'm not saying there wasn't any, I just didn't notice it. For me, the main drawback to LPG was the fact that the tank can never be fully filled (I seem to recall 75% is about the norm) so range on LPG is restricted. Searching out LPG friendly services on long journeys was a concern and the refilling procedure itself I disliked. In Europe I carried various refueling adaptors. Here in LT only a fuel station attendant can refuel your car and the bonnet must be opened.

I think the issues about running LPG cars are are all well known. Despite any drawbacks, I would be happy to run another but, as a low mileage user, I wouldn't bother to convert an existing car.

 

[Joesoap17]

At the time I started using LPG it was accepted that it would use 10% extra fuel and be 5% down on power but it was and still is a small price to pay if you want to run a luxury car on a budget or just save money on any car that has been converted by a good installer.

 

[stephenmercedes]

Crucial to any significance would be the period the car has to run on petrol from cold before switching to LPG. So-how long after a cold start on a winter day does it take before you can switch from petrol to LPG for example? Genuine questionas I have no idea.

My car switches from a petrol cold start to LPG in about 2/3 minutes...

 

[DSM10000]

My car switches from a petrol cold start to LPG in about 2/3 minutes...

Is that all year round or does it take significantly longer in winter?

 

[grober]

My car switches from a petrol cold start to LPG in about 2/3 minutes...

That doesn't seem too bad. Truth be told in this age of computer controlled injection [ diesel and petrol] unless you have air/fuel ratio meter its difficult to know exactly how long we run rich/fast idle on a cold start. Despite all the tricks like variable output water pumps etc diesels always take longer to warm up than petrols- guess its down to their greater inherent thermal efficiency.

 

[Joesoap17]

The Jag V8 was designed for rapid warm up so doesn't stay on petrol for long, but it is about twice as long in winter, but lots of cold starts kill any fuels/cars economy; 2-3 mins on a 75+ mile journey is nothing

 

[s500colin]

I have a 4.7L Toyota Amazon Landcruiser that is Duel fuel Petrol/LPG, the economy
of the Lpg is excellent on a long run last year I drove from Southampton to Norfolk
the cost was £34 would have cost double on petrol.
The main issue I have around southampton is although there is 3 local petrol stations
that stock LPG they all frequently run out and it takes days for them to restock.

 

[Petrol Pete]

Lovely to hear from another LPG fan! Funnily, I also hate the often clumsy install of the filler cap into the cars bodywork, but this installation (done way back) was from a local installer whose work I admire as I've seen him do one with the cap behind the number plate and then 'hinge it', very trick. Of course, my old W203 is pretty neat too with the filler cap beside the tow bar, where you have to kneel down to see it so most don't even know it's there! (I really should have washed those bits before taking the photos!)

Note to self : Always wash your bits before posting photos of them on the internet

 

[Petrol Pete]

Not sure how relevant this is in the real world of running a car. Sure, in a laboratory you may be entirely correct. But in the same way that the official MB MPG claim for their cars can be as wide as 50% off the mark when you actually drive the car, I can only testify what the reality is, and running an LPG car is darn cheap!

I know it's a contentious issue as anyone who has never run one before has natural cynicism, but to be honest, I'm delighted at that.

If everyone started to convert their cars to run on half price fuel, the government would get wind of it and tax it out of existence. Just like they did with diesel, as I'm old enough to remember when diesel was almost half the price of petrol, before the government got their hands on it...

Do I vaguely remember a government scheme some years ago where they helped with the purchase price of fitting an LPG kit to a 'big engine' car provided the car was less than 2 years old ? and the funding 'quietly' dried up ? Or did I dream it ?

 

[zipdip]

Well I have had two LPG cars the first was a Vectra this had factory fitted system,or rather it was taken as a petrol car to I think the Millfield testing centre and changed to LPG, the car ran fine ,it had a large mixing chamber so the car switched to gas in less than a hundred yards fine in the summer but it gave a rough change over in the winter,a full tank would do around 230 miles you soon understood that the gas gauge was a joke so I ran it on the trip,because the company got upset if you used any large amount of petrol,plus points well you could have saved the cost of new oil at a service because the oil was as clean as when it was put in the engine,we never did but I can see it would be a temptation for a owner,we saved about a £10 on the road tax,downsides well you needed a satnav with gas stations marked,filling took a lot longer and in the winter it was a real chore, and the stations always put the gas on a petrol pump and even if the station was half empty there would be somebody on it filling a petrol car looking at you as if you were mad not using the empty pumps there were zero mechanical problems with LPG,but then I suspect the Vectra had a engine capable of using LPG.

 

[grober]

Do I vaguely remember a government scheme some years ago where they helped with the purchase price of fitting an LPG kit to a 'big engine' car provided the car was less than 2 years old ? and the funding 'quietly' dried up ? Or did I dream it ?

I think it was called the Powershift Initiative? On a typical conversion cost of £1400 for 4 cylinder petrol cars that were 5 years old or less the government put up £700 for cars and £800 for light commercials provided the work was done by approved installers. Not sure when this was phased out??

 

[190]

I imagine that LPG is better on emissions than either petrol or diesel. But just like electric vehicles the infrastructure isn't there to support widespread LPG use and in the same way as as EV charging is inconvenient so is filling up with LPG albeit to a lessor extent.

 

[Joesoap17]

I get my LPG from Morrisons, and they are usually the cheapest but it can be difficult to find when away from base so does take planning or an opportunity to run some petrol through the engine.

 

[Deleted member 126969]

From an LPG converted vehicle owners perspective.. I bought a 5.7 Hemi Jeep a few years back and had it converted to LPG. It was high miles for its age and was cheap as a consequence. Overall, after the conversion, it cost me about the going rate for the same vehicle but with average miles.

Since converting it, I've kept a pretty strict tally of costs and including petrol used for warmup, has cost 46% less to run than had it been running solely on petrol. To date, I still haven't covered the conversion cost on fuel savings alone, as I do so few miles these days. As a purely economic thing, it is yet to make sense, but I'm not far away from that now. If I did even close to average miles, it would have paid back long ago. As noted, there is a certain warm glow about filling it up for about half what it would cost for the petrol.

Performance wise, I honestly can't tell if it is running on petrol or LPG, but I certainly don't doubt the science that says it will be a bit down on power compared to petrol. No doubt a dyno would tell the tale. My own figures confirm it is down on mpg, LPG vs. petrol, which is also as expected.

I did have a valve lube system fitted, even thought the installer assured me it wasn't needed on this engine. It was offered FOC so I took it.

As long as the conversion is a good quality one, done well, then buying a car with it already fitted could be a good move IMO. A few key caveats there though!

 

[cheddar]

I did LPG conversions when first started working in garages for a living, going back to 1999-2000. The company we dealt with were stargas, now defunct if I recall correctly.
We were only a small garage, amongst our regular work we did approx 1 conversion a month, almost all of them were regular customers that did high miles, remember diesels weren’t as refined then as they are now, and it was another option.
Most conversions we did were v8 discovery’s and range rovers, with obvious fuel economy benefits on such a thirsty vehicle.
But strangely our favourite conversion was on a 1998 rover 200 (K-series 1.4 16v), known across the motor trade for cooking themselves/eating head gaskets at regular intervals. When I left there to move onto electrics and AC systems, that car was still running great with no issues at 240k miles, spark plugs every service as mentioned in posts above, but the inside of the engine was like a new car. The guy was a yacht salesman up and down the country all the time, he saved a lot on fuel and we never had a single issue with the LPG system fitted since the car was only 6000 miles old.
I’ll always remember that and some of the oddball ones we converted, some with carb’s etc, the only car we had issues with was a vectra used as a taxi. This was due to the taxi company changing the engine after timing belt failure and not sealing gaskets properly.

Now we are in 2018, petrol engine technology and economy has improved considerably, and diesel economy is far better than any LPG equivalent when converted from petrol.

I can’t imagine many new cars getting converted to LPG now, in my my eyes it’s been and gone, fair play keeping ones already done one the road, why not.