LPG Problems Important Notice
LPG PROBLEMS With regard to the ever increasing cost of LPG and the problems associated with Severe Valve Seat Recession on most modern engines (mostly post 2006 vehicles) AMR Autogas have decided to suspend LPG Conversions for the foreseeable future. We will continue to support and service our existing customers' LPG Conversions.This is due to a number of factors as listed below.
List of CARS UNSUITABLE FOR CONVERSION Click Here
LPG PROBLEMS & Economy Drop - What most installers don't or won't explain properly.
The Big Question now is: Are LPG conversions worthwhile now the savings are so small? After converting vehicles for over 15 years we don't think so: The real price of LPG is now 99.87ppl (pence per litre) to equal Petrol mileage.
Please Read Below:
Whilst running on LPG performance is almost identical to petrol but economy is reduced by almost 25%. This is common to all LPG Systems regardless of the make, quality or type. For example a car returning 20mpg whilst running on Petrol will only return around 15mpg when converted to run on LPG. This is because the density of LPG is less than Petrol, Diesel however is more dense therefore more miles are achieved per gallon from Diesel engines see below.
At the moment the average price of LPG is around 79.9 ppl (pence per litre) at the pumps, this is more than twice what it was 3 years ago. With this taken into account to get the equivalent mileage to petrol the correct price of LPG is around 99.87ppl. With the price of gas so high and continuing to rise the savings to be made are very much smaller and obviously you don't save a penny until your conversion is paid for in full, in most cases this may now be several years.
The 2004 Vauxhall Astra 1.6 was available in the UK powered by either Petrol or LPG. This was a factory fitted conversion where the new Vauxhalls had their systems installed and tested at Millbrook Proving Ground, where the engine ECU had been properly optimised for use on LPG, this car achieved 30.4 mpg on the standard test cycle on LPG. Because LPG is less dense and has a different calorific value to petrol as shown below the LPG figure would be the equivalent of 39.2 mpg on Petrol this is equal to an economy loss of 22.45%.
1 litre of LPG weighs 0.67 Kilogram’s with a Calorific Value of 50.35 MJ/kg
1 litre of Petrol weighs 0.72 Kilogram’s with a Calorific Value of 48.00 MJ/kg
1 litre of Diesel weighs 0.832 Kilogram’s with a Calorific Value of 44.8 MJ/kg
All Major Vehicle Manufacturers will exclude any damage to engines caused by the installation ofLPG, including Valve Seat Recession and Burnt Valves under their new car warranty.
All Warranties sold with LPG Conversions do not cover Valve Seat Recession or Burnt valves. Check before buying.
All After Market Warranties specifically exclude Valve Seat Recession and burnt valves. Check before buying.
All LPG Importers and Suppliers will not pay for damage to engines caused by the fitting of their LPG Equipment.
Make Sure: if you do decide to have your car converted to LPG that you ask the installer to give you a written Guarantee that their LPG Conversion, together with any associated equipment including any Flashlube or other type of Valve Protection Systems used are suitable for your vehicle and will not cause Valve Seat Recession, Burnt out Valves or Engine Damage whilst running on LPG, and that they will Pay in Full for any repair costs associated with the above. If they won't do this consider the risks, as repairs will cost more than the conversion in the first place, and the system will need to be removed to prevent the same thing happening again.
Valve Seat Recession Explained
Standard Petrol Engine
Under normal circumstances within a petrol engine during its induction cycle, a jet of liquid petrol in the form of a spray mist is injected from the petrol injector directly on to the inlet valve and into the cylinder thus having a cooling effect. Petrol contains lubricants and additives which reduce valve and valve seat recession wear under normal circumstances to a minimum. After combustion the spent gases are passed through the exhaust valves, these gases still contain some soot, additives and lubricants which protect the exhaust valves from receding and burning into the valve seat. (see pictures below)
LPG Converted Petrol Engine
Once converted to LPG the engine combustion process is much cleaner. When a Petrol engine is converted to run on LPG it is usually by one of the following systems:
A Single Point System, this is a very basic old-type system where the gas is sucked into the engine under its own induction cycle from a gas mixer ring installed at the beginning of the inlet manifold close to the air filter and is then distributed to the cylinders.
A Multi-Point System, is where each cylinder has its own seperate gas injector installed as close as possible to the corresponding petrol injector. These types of injectors inject all at the same time or in groups of either 2 or 3 dependent on the number and formation of the cylinders.
A Fully Sequential System, now the most widely used, consists of again an injector for each cylinder installed as above but these injectors mimic the injection sequence of the original petrol injectors, this maintains the characteristics, performance and driveability of the original petrol engine and integrates better with the engine management system.
In an LPG converted engine the Petrol injectors are turned off by emulators as the engine switches from petrol to gas, (Although in some more expensive gas systems they can be used to inject a percentage of petrol along with LPG ie. 20% petrol 80% gas or other combinations) then the gas injectors take over from the petrol injectors.
LPG is stored in the tank in the form of a liquid, it is then piped to the Vaporiser / Reducer this component is connected into the Vehicle's cooling system. This has two functions, to change the liquid to a gas vapour via the heat from the cooling system causing it to expand around 250 times and also to reduce the gas pressure to a safe and low variable pressure of around 0.7 – 2.5 bar pressure ready to be injected into the engine via the gas injectors.
Figure 1 shows a Recessed Exhaust Valve Click an image to enlarge
Figure 2 shows a Recessed Exhaust Valve and Seat in a cylinder head
Figure 3 shows an Exhaust Valve in a 2006 Vauxhall 1.8 Zafira cylinder head with a large portion completely burnt away after 12,000 miles running on lpg.
Figure 4 shows 2 exhaust valves beginning to burn away.
Figure 5 shows an exhaust valve as it starts to burn away in a few miles it will look like picture 3.
Due to the ever increasing cost of LPG and the unsuitability of most modern petrol engines from around 2006 onwards most now suffer from severe exhaust valve and valve seat recession when converted to run on LPG. This is caused by cheap and poor quality materials being used in the manufacture of the exhaust valves and seats, and also the discontinuation of Manually Adjustable Tappets, Self Adjusting Hydraulic Tappets and engines with VVT Variable Valve Timing.
In most modern multi-valve engines in a bid to reduce prices and ease of manufacture, the makers have opted for fixed clearance or solid tappets which cannot be adjusted without extensive work and often the removal of the cylinder head. These components and materials are fine when running on petrol only, I will explain in more detail below.
This is where the problems with valve seat recession starts, LPG once vaporised is a pure vapour and has no lubricating properties at all, this then passes through the inlet valves and into the cylinder where it is ignited by the spark plugs, combustion takes place and the hot spent gasses exit through the exhaust valves.
Because these gasses are very hot and contain no lubricants or additives they very slowly start to burn the valve face and valve seat of the exhaust valve away, this process (called recession) over time eventually causes the valve to recede in to its seat eventually reducing the valve or tappet clearance to zero. Once this has happened it is only a matter of a few miles before the valve head starts to disintegrate causing loss of compression and misfire. This will also lead to catalytic converter failure if the vehicle continues to be driven with misfires by way off unburnt fuel passing through the exhaust system to the catalytic convertor.
On some cars such as:
All V6 Jaguar / Ford Engines
All Freelander 2's
All V8 Discovery 3's
All V8 Range Rover Sports with super-charged and normally aspirated engines
All V8 Range Rovers manufactured after 2006 with super-charged and normally aspirated engines All the above Land-Rovers now use Ford engines.
Also most Fords
All Vauxhalls after 2006
Subaru, Hondas, Toyotas, Lexus and Nissans can suffer in less than 10,000 miles, even with lubrication systems such as Flashlube fitted these oil injection systems help a little but will not prevent wear entirely.
Pre 2006 L322 Range Rovers with BMW engines and Older P38 4.0 and 4.6 V8 Rover engines are fine and will easily cover large mileages
Caution must be used with Flashlube or similar systems as excess dosing will severely damage oxygen sensors and catalytic convertors. In the past we have experimented fitting hardened valve seats at great expense to Vauxhalls, Nissan X Trails and Primeras along with Flashlube kits and all have suffered valve recession damage within 20k miles the Vauxhall Zafira in fewer than 12k miles
I must stress that not all cars are affected. LPG Problems Cars Unsuitable for Conversion