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LPG'S high price and scarcity, plus a lack of suitable engines, has sidelined it.

Constant hikes in the price of fuel have spurred many petrol-fuelled 4WD owners to look for ways to reduce their bills. LPG used to be the best option.

The mass media is full of alternative fuel stories, but if you’re in the market for a tankful of an alternative fuel to petrol or diesel the only option today, next week, next month and next year is liquefied petroleum gas (LPG).  However, in late 2019 it was no longer a serious choice for nearly all new-4WD owners.

A few years ago you could buy a petrol 4WD and fit an LPG kit to it. The cost of the conversion and reduced economy were quickly amortised by the fuel bowser savings, but that’s no longer the case. A modern petrol engine is much more expensive to convert and the days of engine makers warranting their latest engines for use with LPG are long gone.

On top of that the Commonwealth imposed an upwardly-sliding excise on LPG that saw it climb uncomfortably close to petrol and diesel prices at the fuel pump. When cabbies gave away straight-LPG for petrol/hybrid vehicles the writing was on the wall.

The final nail in the LPG coffin was the very limited number of LPG-conversion-suitable petrol engines in new 4WDs. Nearly all are diesel these days.

Yes, bio-diesel is becoming increasingly added to the diesel we buy at the pump, up to five-percent concentration, but no engine maker warrants a diesel that’s run on pure bio-diesel, unless strict conditions are adhered to.

As for other alternatives, forget natural gas, fuel cells, hydrogen power and electric 4WDs – at least in the short term.

Natural gas won’t liquefy at tolerable pressures, so it needs an enormous amount of tank volume – fine for city buses, but no good for 4WDs – or cryogenic storage, with specialised filling stations and the need to wear safety gear when handling it.

Fuel cells are coming, but not yet. Hydrogen is many years in the future and an electric off-roader awaits improved batteries.

All of which leaves us with diesels in the short term and petrol/electric hybrid 4WDs from 2021.

Those with an interest in alternative fuel history may find the following interesting.


LPG history

LPG came a long way since the early trials on Melbourne cabs decades ago and, although still needing care when being handled, was considered to be no more dangerous than other flammable fuels.

LPG is a mixture of propane and butane, although the butane proportion rose steadily as propane demand approached supply in Australia. These gases are heavier than air and become liquid under relatively low pressures, which means that they occupy around 1/270th of the space they would in the gaseous

LPG is a by-product of oil and gas mining, and oil refining. Its current proportion of the refining process can be raised significantly if needed, but take-up by Aussie motorists was always well short of European and Japanese levels, and is falling rapidly.

There is no possibility of Australia running out of LPG in the foreseeable future and, with more than 2000 retail outlets for LPG, an around-Australia, bitumen-road trip on gas fuel is easily done. However, many of those outlets are abandoning LPG storage, so the situation is worsening, week by week.

Fears that the Federal Government would suddenly raise the excise on LPG and make it a similar price to petrol and diesel seemed to be groundless, since a parliamentary move in late 1988, which transferred wholesale LPG pricing to the Prices Surveillance Authority.

However, excise on transport LPG was introduced in December 2011, at a level of 2.5 cents per litre and that increased to 5c/L in July 2012. The excise schedule for LPG excise was 7.5c/L in July 2013; 10c/L in July 2014 and was capped at 13.2c/L in February 2016.

That sent the retail price of LPG in most areas far too close to that of petrol or diesel.

‘Payback time’ – the period of use necessary to justify the LPG investment – varied greatly, but the LPG Association website had a payback calculator that did the job accurately.

The much-discussed LPG-fitment-rebate scheme – $2000 cash-back for buying an LPG-powered vehicle or $1000 for converting a petrol machine – was never of value to commercial vehicle owners and buyers, because it didn’t apply to business vehicles or those bought on novated leases.


Engine compatibility

LPG burns more cleanly than petrol or diesel, producing fewer emissions but with less output per litre, but when that efficiency loss is measured against its lower purchase price, the attractions of LPG become obvious.

Engine redesign and catalytic converters have done much to clean up petrol engine emissions, to the point where there’s not a great deal more that can be done. LPG is better in emissions terms than most petrol or diesel engines and well below the requirements of the current ADRs.

The negative aspects of LPG on engine life are the fuel’s dry vapour and hotter burning nature. This hotter combustion can cause valve seat recession problems in engines designed before unleaded petrol was introduced. (Valve seat recession is literally that: the valves and the seats wear to the point that the valve sinks into the head, ruining the seal and making correct valve adjustment impossible.)

Of the major suppliers in the 4WD market, only Mitsubishi used to be strongly against gas fuel for its 4WD V6 engines, until the LPG-compatible 3.5-litre was introduced. The four-cylinder 2.6-litre engine coped reasonably well with LPG, but the three-litre V6 did not. Mitsubishi changed the late model 3.0-litre V6’s piston rings, valves and valve seat material in an effort to meet the demands of LPG combustion heat, but still suffered valve seat recession.

The Magna’s dedicated LPG-only V6 never made it into Mitsubishi 4WDs, unfortunately. We had one for years and it clocked up nearly 300,000km, without more than routine servicing.

Historically, Toyota didn’t like LPG conversions, but worded its warranty so that they were not prohibited. The company produced factory-sanctioned LPG car and van models, beginning in 2003. Nissan was much more LPG-minded, being quite happy to see its vehicles fitted with correctly installed gas fuel
equipment and warranted engines so fitted, provided the installation was done correctly by a licensed technician.

Holden had a warranted dual-fuel conversion for the Alloytec V6 that powered Rodeo utes. It was a modern sequential vapour injection system that cost around $4000 and made very little difference to the petrol power and torque figures.

Ford produced the Territory with a dedicated LPG-only E-Gas engine. Original LPG Territorys had a LPG-fumigation system, so output was down in comparison with the petrol equivalent, but 156kW and 370Nm were still respectable figures. Later models had liquid-LPG injection and the same outputs as the petrol

Electronic gas flow controls easily interface with today’s 4WD fuel computers, allowing automatic transfer from petrol to gas. For example, some fuel injected engines fire up on injected petrol, then transfer to gas without driver intervention.

The big development for LPG engines came in 2005: electronic liquid petroleum gas injection (ELPG). ELPG gave better fuel consumption than traditional gas-fed LPG combustion systems, with reduced emissions.

A more recent step was to LPDI (liquid phase direct injection), but its availability in Australia came with an increased conversion price at the same time as retail price hikes, a shrinking number of LPG outlets and a lack of suitable 4WD petrol engines.


Dual fuel conversions

For those who buy or own an LPG-converted 4WD, here’s some information.

Nearly all used-4WD LPG conversions are dual fuel types, in which the vehicle’s petrol fuelling componentry is preserved and the gas components are added. Very few off roaders were happy to commit their fuel requirements entirely to LPG.

The ideal starting point was a 4WD that had twin petrol tanks, because the gas cylinder could replace one of the petrol tanks and therefore didn’t need to be positioned inside the vehicle. Incidentally, when a GU Patrol petrol tank was replaced by a gas cylinder the sub-tank became the remaining petrol tank; when a LandCruiser was converted the main tank was retained for petrol.

Switching from petrol to gas on the move is normally a matter of flicking a dashboard switch, so it’s easy to make the change.

It’s also important to run a tankful of petrol through the engine as often as the LPG installer recommends. This practice is essential for keeping the fuel injection system flushed and preventing stale petrol causing filter or injection pump problems.

Fuel consumption per litre isn’t as good on gas as it is on petrol, with in-service experience showing a 10-25 percent difference.  LPG looks better against a carburettored engine’s fuel consumption than it does against a fuel injected one, because fuel injection greatly improves petrol economy. So, don’t expect only a 10 percent fuel consumption penalty on LPG when you convert your fuel injected 4WD engine – it’ll give up to 25 percent fewer kilometres per litre.

Living with LPG

Tony and Julie Woods are the owners of AJ Automotive in the NSW Southern Highlands and they had a Patrol GU 4500 that ran on LPG.

Back in 2010 we borrowed the Woods’ Patrol for a day’s comparison run with an all-petrol Patrol 4500, owned by an AJ customer, Mel Lane. Both vehicles were automatics and had around 200,000 kilometres on their odometers. Because the Woods’ Patrol had dual fuel, we were able to run it on petrol as
well as gas. We employed a ‘blindfold’ technique – not literally of course – when driving the Woods’ vehicle, so that the driver didn’t know what fuel the Patrol was using at a given time.

With a four-speed auto, petrol Patrols weren’t famous for lightning accelerator response and this test pair was no exception. Patrols liked to be driven with some anticipation and no expectation of ‘jackrabbit’ behaviour.

Petrol definitely had the performance edge over gas, as our roll-on performance figures showed, with faster response and quicker acceleration, but there was no noticeable difference in smoothness. Whether the engines were running on petrol or gas the auto boxes responded faster when set to ‘power’ rather
than ‘economy’ mode.

We compared petrol and LPG performance in several 60-80 km/h roll-ons, with the vehicles in ‘D’ and with ‘economy’ shift engaged. We did the 80-100 km/h roll-ons also in ‘D’, but in both ‘economy’ and ‘power’ modes. The average acceleration times are logged below.

Petrol        LPG

60-80 km/h               4.9 sec        5.3 sec

80-100 km/h ‘E’        6.7 sec        7.0 sec

80-100 km/h ‘P’        4.8 sec        5.6 sec
After this test Tony Woods fitted a turbocharger to the Patrol’s dual-fuel engine and performance was greatly improved, shaving around a second off the above LPG times. Remarkably, fuel consumption didn’t increase in day to day driving and towing conditions.

When Tony and Julie Woods originally fitted gas to the GU their fuel bill dropped immediately and they reckon the payback period was a shorter than they expected.

“We were paying about 60 percent of what we used to shell out on petrol,” said Tony Woods.

“With the distances we ran we paid for the conversion in a little more than a year.

“Amortising the cost of the turbo kit took another year or so!”


LPG reliability

Servicing presents very few additional problems, but an annual inspection by a licensed technician is essential, even where it isn’t a State legal requirement. In-service experience suggests that properly-converted LPG/petrol 4WDs need no more attention than straight petrol vehicles.

“There are specific oils for LPG engines, but unfortunately, most LPG-rated oils don’t match new engine makers’ recommended viscosity indexes,” said Ken Rucker, then AJ’s licensed gas fitter.

“Variable valve timing requires specific viscosity oil, so it’s more important to comply with that requirement than to seek LPG oil.

“Even with the correct oil LPG engines can benefit from metered upper-cylinder lubricant and there is an excellent device from Flashlube that does the job nicely.

“The quality LPG kits we install and look after don’t give their owners much trouble, provided they’re serviced appropriately and regularly.

“There don’t seem to be any issues with the two types currently available – positive feed and air valve systems.

“A complaint we often hear about with LPG engines is backfiring – often severe enough to split inlet air plumbing and air cleaner canisters.

“Sometimes this is caused by incorrect starting technique – flooring the accelerator when cranking the engine, but it’s usually an ignition system

“Because LPG doesn’t ignite as readily as petrol any weakness in the ignition system can result in inlet plumbing full of a gas-air mixture that’s just waiting to go ‘bang’ – and it does!

“For this reason we’re wary of recommending LPG kits for vehicles that have complex plastic inlet manifolds.

“Some LPG installations have ‘pop off’ pressure release valves to vent the inlet system in the event of a backfire, but if the ignition system is in good nick these shouldn’t be necessary

“Gas burns hotter than petrol, so it’s important that the correct, ‘colder’ plugs are fitted

“Major LPG troubles usually start with cheap kits, poor installation and lack of maintenance.

“LPG conversion customers should be suspicious of installation quotes that are greatly different from the average.

“It’s not possible to fit quality components and do a professional installation job for less than about $3000 and most 4WD jobs are up around the $4000-$5000 mark – for a ‘Cruiser there’s the additional cost of a swing-away spare wheel carrier.

“For 4WDs we always fit full-length flexible gas hose, so there’s no chance of pipe cracking – a risk with vehicles that flex their chassis and bodywork.

“A certified installation should come with a compliance plate and a compliance certificate,” said Ken Rucker.