Although the government is heavily promoting the use of alternative fuels like gasohol, which is as much as Bt3.30 per litre cheaper than petrol, a large number of motorists seem uninterested.

Even natural gas, which is much cheaper than petrol, is not gaining popularity among a majority of motorists.

However, there are some people who are interested in lowering their fuel expenses, like khun sale_superman, who has written in with the following:

As a salesman, I need to present my products around the country and need a vehicle that is durable and has low fuel costs. I presently drive a diesel pickup, and in order to lower fuel costs, plan to replace the diesel engine with a petrol engine and convert it to run on natural gas.

Is this possible, and is there is any other way for me to use natural gas with my pickup?

First, the costs that are driving his plan: the price of petrol is currently Bt30 per litre while one kilogram of natural gas - which produces as much energy - costs Bt8.50.

In diesel engines, natural gas can be used with the DDF (diesel dual fuel) system, which basically combines diesel and natural gas and feeds the combination in to the combustion chambers. For small trucks like pickups, I don't think this is an interesting option because it still depends on diesel.

There is another system called "dedicate", which involves installing spark plugs to ignite natural gas and, in this case, the fuel is pure natural gas.

However, the system is expensive and requires highly capable mechanics with an understanding of the system. So it isn't worth it if the truck is going to be used for only short distances each day.

Khun sale_superman's plan - to replace his diesel engine with a petrol engine and then modify it to use natural gas - is easier and promises better results.

But he will need to get a petrol engine in good condition and for a reasonable price. Then its success will depend on the capability of the mechanic who installs the natural-gas conversion kit.

It would be good if he is familiar with the engine model chosen, so there is no need for trial and error. The mechanic should also accurately modify the engine mountings to accommodate the petrol engine. It is important to achieve the right weight balance, or the engine may rattle and shake.

The petrol engine, installation and natural-gas conversion will cost close to Bt100,000.

If the new combination has to be a pickup with natural gas, then I suggest the purchase of a new truck with a petrol engine, which can then be converted to natural gas. This will reduce risks and the chance of errors, but don't forget that it will make the new car's warranty void.

There are two other alternatives: get a diesel truck with very good fuel economy and then use biodiesel, which is becoming cheaper - and would be cheaper still if the government gave it some attention - or buy a small and economical passenger car and run it on gasohol.

Many more motorists should be weighing up these options and making their decisions.

E-mail your motoring questions to

Pattanadesh@nationgroup.com.