LPG CONVERSIONS

sorry I wouldn't touch one with a barge poll. 25 years in the motortrade as mechanic in a dealer and small garage and and fail to see the benefit. cost of fitting/ how long the return...I asked a Toyota Technical chap on a course about them, he wouldn't comment as such but reckoned engines run hotter on them. I have seen many fitted to all sorts of cars from Toyota Landcruisers to M3 Bmws. nothing but hassle when something goes wrong as you go to sort out if it's the conversion or your own fuel/ ignition....just my opinion ..

 

My standard reply to any question about LPG



Written in late 2005 ( as you can tell from the fuel prices !!! )

We looked into converting our 1989 Cavalier 1600 hatchback 4 years ago having driven it on unleaded petrol for the previous 6 months. During this time it returned an overall 42.6 mpg .

I sourced a supplier for the kit who would also commission it and issue the safety certificate.
Price breakdown
Full standard kit…………………......£450
Upgrade to “doughnut” tank…...£100
Commissioning……………….....……..£50
TOTAL……………………………...........£600

I decided to fit the entire kit myself as an experiment and it took the best part of 3 days. Anyone who is reasonably adept at DIY and could, say, fit a central heating system should be able to do the job. But most suppliers will supply, fit, and commission for you and I’ve seen prices quoted from around £900+. They can usually be sourced fairly locally via Free-Ads papers.

The system has been up and running for around 4 years and the vehicle has covered about 70,000 miles using LPG. Per gallon of LPG the vehicle has averaged 34mpg but the savings are from the reduced price of LPG at the pumps.
I’ve not kept track of the relative prices of LPG and petrol over the last 4 years but at the time of writing LPG costs 29.9p ltr ( at Cribbs Causeway – North Bristol ) and unleaded petrol is about 90p ltr. With this price differential over the last 70000 miles ( which it has not been in practice ) we have so far saved around £4000 less the cost of installation.

Put another way, for the price of a gallon of unleaded petrol (90p x 4.546 = £4-09) the vehicle will travel 90/29.9 x 34 miles = 102 miles on LPG.

The system consists of the tank which sits in the spare wheel well and is fed through a filler which I’ve placed near the standard petrol filler. From the tank to the front of the vehicle is the gas pipe and 2 wires, one for the fuel “gauge” (inaccurate!) and the other for one of the systems 3 gas safety valves. Under the bonnet the pipe goes into a filter and then another valve and into the regulator. This regulator is a demand valve which supplies the engine at slightly below atmospheric pressure although it itself is supplied at about 8 bar. Incidentally the regulator was co-invented by Jacques Cousteau who went on to re-invent it for Scuba equipment!

Because the gas on rapid expansion cools significantly, the regulator would rapidly ice up, so it must be heated. This is done by plumbing in the vehicle cooling system to warm the regulator.

So far this description features components common to all conversions. Thereafter it depends on the existing petrol system. On the Cavalier there is a twin choke carburettor and the gas is brought to this by splitting the pipe from the regulator. Fitted between the carburettor and the air filter are the 2 gas mixers and they resemble a gas cooker ring with many small holes and the “ring” is inverted over the carburettor. These gas mixers are unique to the carburettor or air intake system but a vast range of such mixers is available to fit most vehicles.

For fuel injected engines the gas is apparently fed into the air intake. LPG mixes immediately with air and there are no problems relating to worn injectors / carburettor valves. This additionally means that LPG delivers full power on start up.

A dashboard switch controls the 3 gas valves and also a valve which stops petrol getting to the carburettor. The switch panel has a crude system of LEDs which displays the gas level from a float in the tank. It is a very inaccurate and we judge the remaining fuel by reference to the vehicles trip meter.

General Points.

1. Safety. The tank is some 6mm thick, being necessary to contain the gas at around 8 bar and the entire system has many safety features. I would much rather have a crash in a LPG vehicle than in a standard petrol vehicle.

2. Insurance. With reference to the above point on safety, most insurers do not increase the premium but insist on seeing the safety certificate issued by the supplier / installer.

3. Tank. A standard cylindrical tank fits behind the rear seats and would be too intrusive to be even considered. A “doughnut” shaped tank is the answer which is secured in the spare wheel well. The spare wheel can then be placed elsewhere as convenient.

4. Power. The vehicle is definitely lower powered with the LPG supplying the engine, owing to its lower calorific value compared with petrol. If you wished to maintain the power of a 1600cc petrol engine, it would be best to start with a slightly larger engined donor vehicle. Personally I’ve little interest in the maximum power and the 1600 Cavalier is perfectly driveable.
As a matter of interest, in the US, LPG engines have been extensively modified to maintain almost similar power outputs as with petrol (probably at considerable cost ! )

5. Octane. LPG is rated at 105 RON which is much higher than even 4 star. This means the combustion is much slower than with petrol, apparently resulting in a smoother / quieter engine. But it’s not a difference I’ve noticed.
Bearing in mind that this vehicle is one of the last where it is possible to manually alter the timing, I have significantly advanced it in accordance with this increase in octane. This might not be possible with a more modern vehicle with an ECU etc. But I understand there are various “black boxes” which are supplied with more modern dual fuel conversions to adjust the timing when on LPG. They also provide the different advance curve required for optimal LPG usage in a particular engine .

6. Starting on LPG. I’ve heard of conversions where the vehicle starts from cold on petrol and when the coolant reaches a certain temperature automatically switches to LPG. But this has been unnecessary in our installation, as the vehicle always starts from cold on LPG. It must depend on how quickly, on a cold start, the regulator is supplied with sufficiently warm coolant to prevent the LPG icing up .

7. Availability of LPG. Our 50ltr tank gives over 340 miles and larger tanks are available. There are over 1400 filling stations which supply LPG in the UK including an increasing number on motorways. There are lists on the web. Availability is not a problem.

8. Potential price hikes. LPG ( for vehicles ) is not tax-free but has a very low tax rate which is why it is so cheap. Cynics keep telling me that the government might suddenly tax the fuel to a point where it has no benefits, but there is a long term EU commitment to the low tax rate. This is a “green” issue – LPG exhaust emissions being much kinder to the environment than petrol exhaust emissions. Prices around Europe are not much different from the UK.

9. Running out of gas ! No problem. The system is “dual fuel” and at the flick of a dashboard switch the petrol kicks in. This is only occasionally needed as we rarely run out, but we keep a couple of gallons of petrol for peace of mind.

10. Diesels. Diesels can also be converted but it costs more. I can’t really see the point as petrol vehicles are generally cheaper to buy in the first place.

11. Engine wear. Because the exhaust gasses are less corrosive, exhaust systems will last much longer with LPG. This combined with the higher octane rating also means less engine wear. The cylinder compressions in the Cavalier have remained constant throughout the last 70000 miles. In the US ( where there is little fuel price advantage in using LPG ) and Australia, an increase in engine longevity is regarded as a major reason for converting to LPG.

12. Transferability. The Cavalier is coming to the end of its life and we are looking to replace it with a Vectra estate or similar. I intend to transfer the entire LPG system up to the regulator to the new vehicle and then fit new components to supply the fuel injection system.



The Cavalier is our main mode of transport but we also have an air cooled VW camper which I’ve decided not to convert because

a. The drop in power with LPG might be unacceptable on a 1½ ton vehicle with an engine producing just 50 bhp !
b. Being an air-cooled engine the regulator would have to be heated electrically or by ducting exhaust gas. Both of these methods are available as options from suppliers but it’s introducing complexity to a vehicle noted for its simplicity.
c. The camper does a low annual mileage and the payback would be too long to be viable.
d. It’s a classic vehicle which on principle should remain unmodified !

 

Then of course you have to think about this
and if you have children,well i wouldn't put my children in anymore danger than they already are
when just travling on these roads today. Why strap a rocket under your bus.
To be fare i also have thaught about running cost and how to keep it down,all i can do myself is keep the engine in tip top condition and drive smart.

 

at the end of the day you need to do whats best for you,all this help is good, then once you choose stick with it and go for it mate. Would like to see it when its done. An old guy i worked for years ago 8yrs ago lol put lpg in his mk3 cortina and he has still got it today. Your engine will run more hotter,but you can pop the switch and run on normal fuel.

 

For starters if you still drive like I think you do and you're REALLY only getting 20mpg, you need to sort your engine out.
I think you're tipping the figures to justify the install costs. Work it out like your resto - but instead of doubling the costs, halve the savings.
Maybe you should put magnets on your fuel line, a special sack of lead in the tank and a "spitfire mult-spark" lead on your ignition too...

 

2 of my previous customers have the conversions. Both were very happy with them. Both ran on 100% gas by which I mean they started from cold on it, despite being warned by their fitters that they wouldn't. Neither were technical types though. That is all I know.
Apparently, you need no qualification to fit these (or didn't 3 years ago), but "must be able to show competency". I'm surprised by the need for an insurer to have paperwork. They don't ask for it when you fiddle with the petrol/carbs etc?