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Published on January 9, 2008

 So many people are caught up in the annual exodus that fuel stations in Mae Hong Son and other places like Pai can run out of diesel. So from mid-December right up to New Year's Day, my phone was running hot.

I was lying in bed with the flu, but still a lot of people called to ask me about various routes they could take, and many motorists who were travelling to Mae Hong Son called because they were unable to buy diesel from large petrol stations. They asked me whether it was all right to buy diesel from small roadside shops in rural areas.

Every time, I asked whether they were using a vehicle with a commonrail diesel engine. If the answer was yes, I recommended they not risk using fuel sold from barrels with glass measurement equipment. The fuel-injection systems in commonrail engines use very fine jets, and if the fuel is not really clean, there is a chance it can clog the system, resulting in hefty repair costs.

When fuel is sold from 200-litre barrels, it is drawn up manually into a 5-litre glass container before being emptied into the vehicle's fuel tank. It is easily contaminated, because there is no filtering. The barrel is also made from steel, and it is easy for water droplets to form from moisture when the temperature changes from hot to cold.

There is also another type of fuel station with just one or two filling points, but the fuel tank is built on top of the ground rather than underground as in standard fuel stations. This type of station should also be avoided by vehicles with commonrail diesel engines, because there is a possibility there could be water or other dirt in the fuel. The fuel nozzles also do not have filters.

If your vehicle has a normal diesel engine and you cannot buy fuel anywhere else, then you can use these small roadside places, because the fuel-injection system in your vehicle has much larger jets. Even if they become clogged,, they can be fixed cheaply. You can even clean them yourself. But with commonrail engines, you'll have to take the vehicle to a service centre.

Some travellers to the North also say their exhausts blow white smoke when driving up the mountains despite the fact that their engines are still new. This is caused mainly by the cold air in the mountains, and a little bit of white smoke from the exhaust is nothing to be worried about. You don't have to do any fixing.

However, if there's a large quantity of smoke from the exhaust pipe, think about your last fuel refilling. If the fuel was not clean, there could be white smoke. This can be tested by checking the fuel quality.

Catch some fuel before it passes through the fuel pump and pour it over a piece of tissue paper. If there are any black or brown specks in the fuel, or if there is any water (sometimes the fuel will appear slimy), then you can be pretty sure that the fuel in the tank is dirty. Once you get the vehicle down to an area that has a service centre, have the fuel system totally cleaned.

Another common cause of white smoke when driving at high altitudes is moisture clogging the air filter. Thailand is a tropical country, and in the winter there can be a lot of moisture in the air. When the engine sucks in air through the filter, it also sucks in a lot of moisture, which can clog the filter. If this happens, only a small amount of air is able to enter the combustion chamber, resulting in an unstable air-fuel ratio. This can cause milky white smoke.

E-mail your motoring questions to Pattanadesh@nationgroup.com.

Pattanadesh Asasappakij

The Nation

Ultimate in Luxury

The Luxury LS 460 is a wonderfully comfaortable car fitted with all mod cons, althoough not necessarily the most fun vehicle to drive.