LPG CONVERSION PROS AND CONS QUESTIONS.

Discussion in 'Mech Tech' started by Poptop2, Jun 22, 2013.

  1. Poptop2

    Poptop2 Moderator

    I have been thinking about this for some time, i have seen secondhand conversion kits on ebay for about a hundred quid and i should be quite capable of fitting one given the correct instructions and providing we are allowed to do this without special equipment.

    So my questions are -

    Are they vw aircooled 1600/2.0 specific.

    Are they something we can do ourselves

    Where do you store your gas tank.

    What goes wrong with them commonly

    What should you check for when buying one on somewhere like fleabay.

    Any other info would be gratefully recieved too :thumbsup:
     
  2. We've run lpg cars for the past 180,000 miles but decided against converting our 1979 a/c camper.

    Below are some notes I made a few years ago for info - hope it helps

    Original LPG thread, 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 !
     
    PanZer, JLB, CSI_Will and 1 other person like this.
  3. Poptop2

    Poptop2 Moderator

    Absolutely Brilliant probably the best reply i have ever had on here bar none, Thank you :thumbsup:
     
    PanZer likes this.
  4. Moons

    Moons Moderator

    Great answer Mike!

    I had an LPG system fitted professionally to a Peugeot 406 Coupe - the V6 one - it categorically ruined that car, this was on 2002/2003 - I've seen no evidence that the technology has improved since then.

    I agree that LPG is good on older cars with single point injection or carbs - but on anything multipoint with a clever ECU - I doubt you can get it working reliably - this is born out by both Ford and Vauxhall dropping their LPG fleet offerings (due to crankshaft premature wear and emissions) and pretty much no one running LPG equipped cars professionally (even the taxi's have ditched it).

    That car was in and out of the garage, was sent off to the kit manufacturers and even had some fella come over from Italy to take a look at it - it spend 18 months invariably stalling and was in and out of the garage all the time (I want to state that the car was in really good nick with well below average mileage).

    My observation is this simple - anything that needs a controller that piggybacks the car's ECU (as opposed to remaps it) is doomed to failure as as far as I can tell it primarily 'fools' some of the sensor readings that the car's ECU uses and that delay is catastrophic.

    Less intelligent car's I think are fine as they use far fewer parameters to make them run - so in the context of a bay most of the above is babble.

    My only other observation is that whilst garages state they sell the stuff - often, they have run out or the pump is faulty (my brother runs a V8 Discovery on LPG and likes it, but supports my garages observation).
     
  5. I didn't read it all, it was about 20 mouse roller moves to many for me!
    But interested to know what you've decide mr pop o top?
     
  6. Moons

    Moons Moderator

    I agree that the oils seems to be clearer for longer with LPG - but I also know that a lot of places sell flashlube kits to stop valve seat regression and a lot of factory LPG conversions failed on the crank and cam shafts (unsure why the crank might go, I guess hotter heads on a OHC engine might cause cam issues) - neither of which are obvious on a compression test.
     
  7. Poptop2

    Poptop2 Moderator


    i am open minded atm Oscar as that is just one persons thoughts/findings!

    i would be interested to hear from someone who has run a bay on LPG and can give a balanced account of their experience with it.
     
  8. We eventually scrapped the Cavalier (rust) at 180,000 miles when the engine was still running perfectly. Since late 2005, we've been driving a Vectra 1.8 year 2000. Bought and immediately converted at 100,000 miles, we've now added another 115,000 miles driving on LPG and it's been faultless! It's a "modern" car, with fancy FI, electronics etc and the lpg adds another box to do all the clever stuff. It's never missed a beat and saved a fortune in fuel. As for the vehicle itself, we've only changed the oil/filters/belts at the recommended intervals, and the only time we've changed the exhaust was after 110,000 miles of driving! It's sounds and drives like a new car, that's modern technology for you ;)

    As a petrol vehicle, we'd expect an overall 40mpg but the lpg takes this to about 72 mpg. (A Vectra is a big heavy car, something like a 1200 Fiesta/Corsa etc, would give the equivalent of nearly 100 mpg !)
    This means we would have spent around £17,300 driving the 115,000 miles on petrol, but have actually spent around £9,600, saving about £7,700 less the conversion cost of about £900.
    I reckon we've spent around £300 on servicing the LPG system.

    Four years ago, we drove the lpg Vectra to Austria and back, a round trip of about 2,500 miles. It cost about £210 in lpg, but would have cost about £375 in petrol. To drive the petrol T1 camper would have cost over £675 !!!!

    This (almost rustfree) 13 year old/215,000 mile Vectra is running perfectly and will hopefully last a long time before needing replacing. When it IS replaced, we'll certainly be looking at LPG to continue our discount motoring ;)
     
  9. Moons

    Moons Moderator

    Sorry Mike - but the web is littered with confusing maths on what cars will do and not do on LPG - and pretty much all of it is promoted by the LPG industry. This includes the LPG Calculators and hopelessly optimistic and misleading quotes.

    When you quote MPG figures - you need to stick to the mechanical facts and not use equivalent running costs to then extrapolate the performance figures i.e. a car that does 40mpg on Petrol does not do 72mpg on gas - gas is approximately 20 - 25% less efficient than petrol, i.e. you need to burn more of it to get the same amount of energy, so if we took your Vectra as 40mpg on Petrol it would run at approximately 30mpg on Gas.

    If anyone wants to test this put 1 gallon of Petrol in a car and get to 40 miles then konk out, put 1 gallon of LPG in a car and you will get to around 30 miles, not 72 before you konk out.

    If we then take those figures and use your 115,000 miles as the distance figure I make fuel used as:

    115,000/40 = 2875 Gallons, or 13070 litres of Petrol
    115,000/30 = 3833 Gallons, or 17425 litres of Gas

    Again, another assumption is that Gas is always half the price of petrol, when it can vary - so I'll take the figure from today's prices on PetrolPrices.com Petrol £1.34 Gas £0.70

    So cost of fuel used is:
    Petrol - £17,513.80
    Gas - £12,197.50 (even with an absolute best figures it's still £11,433.80 - after that we are in to defying the laws of physics)
    Interestingly, a diesel Vectra would to the above mileage for £14,533.84

    Note the figures above don't factor in variables such as the additional weight of the LPG system (i.e. I'm not using real world maths, just the difference if you used the car statically where weight and change in driving habits don't factor - and what I mean by that is if your car is running 20% less power people tend to use the accelerator harder to get the same performance), how much petrol is used on start up (or are you still able to run a FI car without petrol to warm it up) and rerouting to fuel on LPG (assuming you don't have a local LPG garage) - also, I haven't factored in variation in fuel cost across the actual time it would take you to get to 115,00 miles. I've also assumed a combined cycle MPG.

    Finally - and probably most pertinently - I haven't factored in how the car burns the fuel - Petrol engines are optimised for Petrol - if you were to design an engine that was optimised for Gas only I would imagine it would not have the same inlet tract, ignition system etc - this is born out by the fact that the best LPG systems now use direct injection of the liquid rather than gas/air in the intake manifold. By this I mean that the engine itself does not run at 20-25% less efficiency, just the fuel itself (I've used energy density of both fuels by volume unit and not the other trick that the LPG industry uses to fog the facts, calorific value) - I would speculate that the difference in performance is wider still due to this.

    I can't get your Austria figures to match my workings, am guessing you have simply taken a financial value and extrapolated it on to petrol costings - my maths is showing your car is running equivalent to 38mpg on Gas which is quite frankly amazing/impossible. If the financial figure of £210 is accurate - then this distance figure is out.

    I have a feeling we'll never see eye to eye on this one - the web demonstrates how the LPG industry crowds any research a consumer might want to do with unachievable real world figures, most of which defy the laws of physics - but then by observation it is an industry remarkable only by how many 'expert fitters' disappear each year thus voiding their promises of guarantees.

    I had an extremely bad experience with LPG and would not recommend it on a modern car. You've had a very positive experience with it on both a modern and older car.
     
  10. how about a hydrogen fuel cell conversion? i know nowt about them but seems to be the future...
     
  11.  
  12. I've done over 10,000 miles in my t25 caravelle on LPG without any significant problems and it returns about 16-17mpg around town instead of the 19-20 i got on petrol.
    Even at the 76.9p/l i have to pay for LPG it still works out nearly 10p/mile cheaper than running on petrol.:)

    Sure theres some horror stories of engine failures and bad installs but thats the same with every vehicle. Just look at the amount of failed coil packs on new VWs over the past few years.
    Only thing with converting an aircooled vehicle is the fitting of a probe in the exhaust for heating the LPG. I'm not sure but i think the current rules don't allow that anymore so another option is needed. Maybe an oil cooler heater or something.
     
    Poptop2 and Molteni Mike like this.
  13. Poptop2

    Poptop2 Moderator

    Thanks for your replys thus far, i am still unsure tbh but keep them coming :thumbsup:

    Just to remind you of my intention, i will be buying second hand off somewhere like ebay if i decide to do it so would need to know exactly what i am looking for - ie bits missing , important bits that wear and what sort would suit the bay :)
     
  14. Poptop2

    Poptop2 Moderator

    i have looked at this and emailed a few sellers, it appears they do not work re helping fuel consumption but do improve the efficiency of the carb and running of the engine, however everyone says you can't get something for nothing re fuel and the gain in efficiency is offset by the extra power needed to charge the fuel cell, can't see that myself as it is minimum input needed to power the hydro fuel cell and it does not drawer extra power when under load it just trickles hydrogen into the air filter and is created by excess 12v that your dynamo produces?
     
  15. How can the engine be running more efficient if its still using the same amount of petrol:confused:
     
  16. Poptop2

    Poptop2 Moderator

    Smoother acceleration cleaner burning so i have been told, i imagine if this is true then it can only be down to the higher H in the the mix. So smoother running better efficiency :thumbsup:
     
  17. Better efficiency is either more power for the same amount of fuel or the same amount of power for less amount of fuel

    If an engines using the same amount of fuel with no increase in power then it isnt any more efficient
     
  18. I think you'll be hard pushed to source all the components secondhand from eBay because you'll need both a heating system for the regulator and the mixer, which will be unique to your carb. But if you can get everything else and only buy these as new items, you'll save a bit. Remember that you'll need a safety certificate to keep your insurers happy :thumbsup:
     
  19. Poptop2

    Poptop2 Moderator

    So how do you go about getting a safety certificate Mike?
     

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