17 April 1998



Odd place, a yacht basin,

to find something that might

help reduce farm costs. But

Lymington, Hants, is home

to more than sailors as

Andrew Pearce discovers

ONE of the cost bugbears of farm runabouts is filling the tank. Not so much for those with a modern diesel 4×4, but definitely so for anyone with a petrol-swigging Land Rover or a big-engined behemoth.

Moving to diesel power is one improvement, for Dr Rudolfs clattery inventions always deliver better economy in short-trip and light-throttle use. Often though, engine swap cost knocks that one on the head.

Another possibility is to use a cheaper fuel. Dual-fuel conversions which let an engine switch between petrol or liquified petroleum gases (lpg) have been about for years. But they have never really taken off in the UK, probably as filling stations have been few and far between, because both engine output and economy suffer, and to carry the stuff means losing boot space to a socking great propane tank.

&#42 Cheap and green

So whats changed? According to Hants-based specialist Marine Eco Power, quite a lot. Not the fuel – its still a bargain. Bought at the pumps with duty and VAT paid, lpg is around 39p/litre, a 43% cost saving over unleaded petrol at 68p/litre.

You cant usually make up for the loss of space in the vehicle, unless its possible to fit one of todays spare-wheel-shape toroidal tanks. But modern electronics controlling the lpg system, plus todays efficient engines, have apparently got around much of the wastefulness of traditional setups. So power output and economy take less of a knock.

And lpg is decidedly flavour of the month in Westminster, as it produces significantly lower gaseous emissions than petrol and virtually no diesel-style particulates. So much so that the government dropped road fuel propane duty by 15% in 1995, 25% in 1996 and froze it in 1997 and 1998.

On top of this, last months Budget offer of a £50 road fund licence discount for clean vehicles may well apply to lpg users, though this wont be revealed until the Autumn.

&#42 Telling the difference

At Marine Eco Powers base we tried a 1993 Vauxhall Cavalier and a 1995 Rover 800 Vitesse, swapping energy source using the dash-mounted control pod. Both cars started on petrol, then within a minute switched themselves to lpg.

It was hard to find a real difference between fuels. The Cavalier lost a little acceleration, the turbocharged Rover still went like the clappers. The biggest difference came at switching to gas at tick-over, which noticeably smoothed out the idle.

Are there any engine concerns, we wondered? Catalysts are happy to live downstream of an lpg conversion, say the specialists. But for long life, older engines that normally run on leaded fuel will normally either need a conversion to harder valve seats (around £175 for a 2.25-litre Land Rover), or be fed a metered supply of upper cylinder lubricant. If neither course is taken and the engine isnt thrashed, valve area problems will probably take a while to show.

Liquid petroleum gas proponents also reckon there are maintenance savings to be made with any motor. Oil is not diluted so can serve longer, plugs get an easier time and theres less carbon build-up.

&#42 The cost/benefit thing

Marine Eco Power says that its Italian Lovato equipment, working on a modern engine, lowers economy by not more than 5% and reduces power output by 3%. With older motors, fuel use will rise by 12% maximum and power drop by 5%. These figures are at odds with the national LP Gas Associations umbrellas of 20% extra fuel use and 0.5%-2% power drop, but the Lymington company points out that its equipment is state-of-the-art stuff, and that the associations figures both include all equipment on the market and go well back in time.

Lovato kits cover carburettor engines, fuel injection motors and turbo variants, with the latter two more expensive as electronic control boxes are needed.

&#42 Payback period

Typical supply/fit cost for a carburettor motor is £700-£750, plus VAT. This gives an 85-litre (18.7gal) lpg tank and covers such things as old Land Rovers, V8 Range Rovers, Landcruisers and Patrols, with the original petrol system completely retained for dual-fuel use. Fuel injection conversions span £1000-£1300 depending on the make and model, which is substantially under the cost of a diesel engine swap.

Payback period depends on use. Before jumping in to a conversion its essential to work out the economics for your own situation, so heres a "for instance".

If a car covers 10,000 miles/year at an average of 20mpg, the bill for unleaded petrol at 68p/litre comes to £1543. Running solely on garage forecourt lpg at 39p/litre, fuel cost shows a saving of £658. So in less than two years a carburettor conversion pays for itself, while the most expensive injection kit will be covered in under three years.

All this assumes, of course, that you can find a source of lpg. Calor – the UKs biggest supplier – says expansion of its supply network over the next two years will add 140 or so more sites, bringing the national total to 300-500. But most new outlets will be close to towns.

Of course you can install a bulk tank, with the options depending on supplier. Some things always apply – any unit must be sited on concrete with at least 3m (10ft) clear space around, have room for the vehicle to stand 3m (10ft) clear of the tank during filling, and there must be physical means to make sure this distance is maintained.

&#42 Bulk tank rental

Calor puts in a 2000-litre (440gal) vessel as minimum. Tank rental is £32/quarter, to which has to be added around £40/quarter for dispensing equipment. Although lpg in bulk will then cost typically 18p-19p/litre, duty (10.56p/litre) and VAT have to be added if the vehicle(s) are to be used on the road.

Other companies are happy to supply smaller volumes. As long as propane usage will be not less than 10,000 litres/year, independent supplier Flogas will install a tank for free then charge £50/quarter rent, including dispensing equipment. Its gas price starts at 17p/litre plus duty and VAT (still under forecourt cost) and falls if product use goes up.

Either way, to see substantial benefits other than convenience from bulk buying, a farm will need to run more than one gas vehicle.

Worcs farmer John Keel converted his G-reg Range Rover to propane. The tank does take up some boot space; he also reports that consumption is about 5mpg poorer. However the vehicle performs better and is quieter. Left: The basics of a Lovato lpg conversion. A second tank with filling valve and contents gauge to go in the load space, a vaporiser to deliver gas (centre), various solenoids to direct the flow of fuels, and a filler coupling.

Heres the vaporiser fitted to a Rover Vitesse, with a flow solenoid to the right and control units just visible at the top left. Vapour from here goes to the engines inlet manifold by swirl-hole sandwich plate, fitted either below a carburettor or in front of an injection systems air flow meter. A blow-back valve vents manifold pressure in case of backfire.


&#8226 A by-product of natural gas production and oil refining, propane is burnt by dual-fuel engines.

&#8226 In the car its stored as a liquid at around 6 bar pressure (90psi). Fuel is drawn off, is turned into gas by a vaporiser and goes to the motor – see pictures for the hardware. Safety for occupants comes from a tank that stands at least 32 bar (470psi), copper feed lines, and the fact the lpg in air ignites in a narrower band of concentration than petrol.

Normally, a cylindrical standard tank sits in the boot with its own filler connection. Alternatives are a toroidal unit to go in place of the spare wheel, or multiple and more expensive smaller tanks under the floor pan.

Above: In the cabin, a switch similar to this controls manual fuel switch over (if needed) and shows lpg tank contents.

Left: Liquid propane is pumped between tank

and vehicle across

a sealed coupling.


Claimed lpg pluses are:

&#8226 Lower fuel bills.

&#8226 Lower exhaust emissions.

&#8226 Lower maintenance costs.

&#8226 Longer engine life.

&#8226 Smoother running.

&#8226 Dual-fuel use boosts vehicle range.

&#8226 Can switch between fuels on the move.

&#8226 Possible future discount on road fund licence.

Negatives are:

&#8226 Relatively few filling stations.

&#8226 Power output down by 3%-10%.

&#8226 Consumption volume up by around 5-12%.

&#8226 Likely loss of vehicle interior space to lpg tank.

&#8226 Conversion cost high in proportion to older vehicle value.

&#8226 Valve seat recession in older engines requiring leaded fuel.