Is LPG still worth it?

Posted on March 24th, 2015 by Rob Marshall

lpgAn interesting letter was published in the spring edition of GEM’s membership magazine, Good Motoring, by a member that championed the case for running a car on gas (LPG) and queried why it is mentioned so infrequently. The writer has a valid point. The fuel costs approximately half that of standard unleaded and, although the tax breaks are not as generous as they once were, LPG still offers a significant saving.

The downsides put many people off. The cost of a good quality conversion tends to run into four figures easily and so a lot of miles have to be covered, to make any kind of realistic payback viable, within a reasonable timeframe. In addition, the system requires servicing annually and you still cannot take an LPG-powered car on the Eurotunnel. The space required for the additional fuel tank (which is not as accommodating as a petrol tank) can rob the car of either its spare wheel well, or significant luggage space. Despite costing less per litre, an engine tends to be thirstier on LPG, compared to unleaded, which gives it a lesser range. I was also concerned that I could not find a single manufacturer that offers a gas-powered car for the UK market, possibly due to the limited number of fuel stations that stock LPG.

However, with diesel engines having been demonised currently (a topic that will have to wait for another blog), the trend for converting a petrol engine to LPG might make a comeback. However, things have changed in the last decade and it appears that many modern vehicles have become increasingly intolerant of the drier-burning fuel. We have heard of an increasing number of cases, where LPG-converted engines have started to lose compression, as a result of either damage to the exhaust valves and their seats, which can cause a problem called valve seat recession. The same problem used to exist on old cars that were run on unleaded petrol, when they preferred a diet of the old four-star leaded.

Some reports suggest that the reason is due to a significant number of (but not all) engine manufacturers tending to use softer (maybe cheaper) materials for the cylinder head’s inserts and exhaust valves, plus modern engine designs have removed provisions for quick and easy, manual valve-gap adjustments. So, once you have factored in the cost of a cylinder head rebuild, with new hardened valve seats, or you have decided to equip the car with a valve lubricating additive, LPG conversions become an even less appealing proposition – which is a pity.