LIke to convert to propane, but what do you think of this ?
If LPG was so good and cheap, why don稚 we run all our vehicles on it? The truth is, converting a petrol motor to run on gas will lead to more problems than it solves and may cost more in running and repair costs than an unconverted engine.
An unmodified internal combustion engine designed to run on petrol will not perform as well on gas. The most obvious symptom of this is reduced engine power. Gas installers will claim anywhere from 5% to 10% loss but in reality it can be much more, as high as 20% and while you may not notice the difference driving around town, itç—´ on the open road and ascending hills when an LPG fuelled vehicle falls behind. To compensate for reduced engine power, you need to push the motor and this means revving it in lower gears to get up the hills. An engine which is worked harder like this will use up more fuel and wear faster, not to mention the strain on the transmission. A 6 cylinder engine will of course perform better than a 4 and suffer less wear. Don稚 even think about converting a car with an engine capacity less than 2 litres, theyæ±*e too gutless
In addition to the power loss, LPG consumption is greater than petrol. Figures vary considerably depending on whom you talk to but 30% less distance per litre compared to ULP is not an unrealistic figure. It may be cheaper than petrol but you have to fill up more often to travel the same distance.
LPG performance can be improved by fitting a high compression head but this pretty much wrecks the carç—´ ability to run on petrol and then thereç—´ the cost of the replacement head and installation cost. The Engine Management System also needs to be tuned for LPG, thus reducing the motors ability to perform efficiently on petrol.
By far, the worst thing about converting your car to LPG is the head and valve damage it causes. LPG is a dry fuel which ignites at a higher temperature than petrol. The higher temperatures will, repeat, will burn out exhaust valve seats and valves over time. Known as Valve Seat Recession, (VSR) the valve seats recede into the head and cause loss of compression for the affected cylinder. Left untreated, the engine will progressively lose power, use more fuel, idle roughly and stall and tappet damage will occur. When this happens the only solution is to replace the valve seats and valves or even the whole head. Expect in the order of $1500 to $2500 for this to be done. High ignition temperatures can also warp the head, necessitating costly replacement. When a head is replaced on an LPG vehicle, hardened valves and seats must be fitted although there is no guarantee they will last.
VSR can occur surprisingly quickly on some engines, after as little as 50000 Km and there is no way of knowing if your motor is susceptible. LPG vehicle installers will never mention VSR to customers and if pressed will dismiss it as a phenomenon that only affects older engines. Not true. Fitting an upper cylinder lubricant dispenser such as Valve saver is reputed to reduce VSR but once again there is no guarantee. The dispensers must be installed correctly with the outlet line tapped into the inlet manifold after the throttle butterfly in a central position so that the lubricant spray is distributed evenly to all cylinders. Many mechanics simply attach to a vacuum line that only feeds to the 1st couple of cylinders. Many lubricant dispensers are extremely fiddly to set up and require constant adjustment. Often they stop dispensing altogether. There is also the additional ongoing cost of the lubricant to consider.
Valve and head problems are not the only temperature related issues either. Spark plug electrodes burn out, resulting in poor performance and contributing to backfires. Expect to replace your spark plugs every 20000 30000 Km. And by the way, not just any spark plugs will do. For LPG it is recommended that ç”°old plugs be used. The spark gap has to be set shorter as well.
If you are running on LPG all the time (and why wouldnt you after all it is cheaper than petrol) you may find the injectors block up through under use. When switching to petrol, expect rough running, a rich mixture, surging and pinging. Injector cleaning is expensive and if the injectors are kaput, you need to be sitting down when given a quote for replacements.
Still keen to convert? It gets better
The realization you have made a dreadful mistake converting your car to gas occurs when you have a backfire. This is LPGç—´ dirty little secret. Modern engines use an air flow meter as part of the engine management system. It sits just after the air cleaner and essentially tells the management system how well the engine is running. It is a vital piece of equipment. The critical component of the air flow meter is a wafer thin filament about 10 mm long. If LPG in the inlet manifold ignites, we have a backfire which is really an explosion. Not good. The car stops dead, hoses get blown off, the inlet manifold can burst and that delicate little filament is no more. In extreme cases you may throw a timing belt or worse. Much worse.
Your engine management system has registered a catastrophic failure and will probably set itself to æ–—imp home mode If you are lucky enough to get the vehicle going, it will probably go no faster than 80 KPH, idle rough, run hideously rich and is useless for all but a trip to the garage. A replacement meter will cost $750 upwards. Gas is not so cheap after all if you blow several of them. Inexplicably, some vehicles will run OK with a blown meter on LPG but others wont
How can a modern engine backfire? It should not be possible on a fuel injected motor. Most LPG conversions use a single point injection system. LPG in it痴 gaseous form is simply injected into the inlet manifold, like a rudimentary carburetor. When switched to gas the petrol injectors are switched off (this is the main reason they clog, they don稚 get used enough) A number of conditions make backfires happen. Because of the high temperatures, there can be hot spots in the cylinders, namely eroded valve seats, valves and spark plugs. The gas mixture entering the cylinder ignites prematurely before the inlet valve closes and the resulting explosion travels back through the inlet manifold. Incorrect mixture is also another prime cause of backfires. Pumping the accelerator on starting will do it as will an incorrect installation. Some systems, particularly those on factory fitted new cars won稚 start the engine on gas. The motor is started on petrol then switches over. An antibackfire flap can be fitted but there effectiveness is pretty limited. Some people in desperation have cut holes in the inlet manifold and put rubber plugs in them so they blow out or stick on masking tape so it blows before the meter.
Newer so called 4th generation LPG conversions use sequential multipoint injection instead of the single point arrangement. The claim is that all the problems of older systems are eliminated, particularly backfires. The backfire claim may be true but the VSR and performance issues are likely to remain. Fact is, many of the older systems will still be sold to unsuspecting customers and apparently only vehicles manufactured after 2004 are eligible for sequential multipoint kits. The Governments LPG grants scheme also applies for second hand conversions, so the older systems will still be installed for a while yet. Manufacturers and installers have sold single point injection kits for years claiming them to be trouble free so thereç—´ no reason to expect any different from them with the newer systems.
And thereç—´ more?.
LPG conversions are awfully touchy and can go out of tune very easily. The weather is a good example. Your car may run great during the cold dry winter months but come summer it starts playing up. At least every 20000 Km take it in for a gas service and that means more cost.
Power steering and brakes can place a lot of strain on car engines. Itç—´ common for LPG converted vehicles to stall when pulling to a stop and turning. On some vehicles this happens frequently on windy days (seriously). The Oil companies have a different petrol blend for winter and summer. Autogas is the same the year round. The NSW Government spent lots of money converting police vehicles to LPG only to have many of them stall all the time, often during chases.
Not all vehicles are suitable for conversion. If you have a 4 cylinder sedan or hatchback, forget it. There is nowhere to put the tank. Even six cylinder fords and holdens lose cargo space to a gas cylinder. Vans, utes and 4WD usually have room where the spare wheel fits under the rear of the vehicle but you need to find somewhere to put the spare. The gas tank often hangs down and bangs on some driveways. The exhaust may also need to be rerouted which may cost extra. Some gas tanks are now designed to fit the spare wheel well but you still need to stow the wheel.
LPG conversions must be done by an accredited installer, however this is no guarantee the installation will be performed competently. All vehicles are different and require a separate kit for each make and model. It takes years of experience to learn the nuances of LPG conversions and there is no one size fits all installation. Fitting a gas kit to an older motor is going to cost you plenty in the long term unless you retrofit a gas compatible head, with hardened valves and seats
Even without factoring the cost of likely repairs and maintenance. You have to drive an awful lot of K痴 to recover the installation cost. Figures vary but I致e heard 30000 Klm per year. If you drive less than 20000 Kilometres every year it痴 probably not worth it. The irony of the grant is that commercial vehicles that do a lot of travel will be ineligible
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