Two years ago, he downgraded from a 2.4-litre Honda Odyssey to a smaller car because he wanted to cut his petrol bills.

True, petrol prices have gone up, but he claims his Nissan Sunny is also giving him lower mileage.

Some Sunny owners can travel 10km on each litre of petrol.

Yet Mr Lee Teck San, 47, says his cars takes him only about 270 km each time he puts in about 40 litres, which works out to less than 7km to the litre.

The noodle hawker has no idea why his 17-month Sunny is a petrol guzzler despite multiple tests.

Said Mr Lee: 'My petrol bill might not seem a lot over a month or two. But over 10 years, it can amount to a big sum of money.'

He travels an average of 30km a day.

His frustration over petrol started early. Soon after he bought the car, he noticed that he could do only 290km on a full tank, before the low-fuel indicator would come on.

Each time he filled up, the 50-litre tank would take about 40 litres.

Watching the fuel level like a hawk, he discovered that from one filling to the next, he was averaging just 270km.

Mr Lee, who had bought the car from an authorised agent, went to Tan Chong Motor, the distributor of Nissan cars, with his problem.

He has taken the car to them thrice.

And each time, they checked the car and found nothing wrong with it.

As the car is covered by a warranty, he did not have to pay for the checks.

When contacted, a Tan Chong spokesman said: 'In times of high fuel prices, naturally, customers feel the pinch more.

'Generally, fuel consumption levels differ with each driver depending on his individual driving habits, usage patterns, and road conditions.'

The spokesman said Tan Chong has received both positive and negative feedback on the fuel efficiency of the Sunny.

When The New Paper on Sunday made two calls to Tan Chong's showroom in Ubi and to its service centre in Toa Payoh to ask about the Nissan Sunny, the staff there confirmed that the car should average 400km on a full tank under Singapore's road conditions.

Other Sunny owners The New Paper spoke to had mixed reactions when they heard about Mr Lee's complaint.

MYSTERY OVER FUEL EFFICIENCY

Miss Rachel Tong, 36, who has had a Nissan Sunny for three years, said she often gets 400km out of a full tank, that is about 10km to a litre.

But Mr Tan Hong Lin, 71, who has driven a Sunny for four years, said he averages less than 300km on a full tank.

Even when he travels long distances on Malaysian highways, he gets only 300km.

'It's very hard to hit 400km in Singapore because there are so many traffic lights,' he said.

So what could be behind the lower than expected fuel efficiency?

Mr Pang Tsun Bin, 24, a mechanic, said a car with a leaking fuel tank or faulty safety valves would consume much more fuel than normal.

A routine check would expose these problems, he said.

Poor driving habits in general could also jack up petrol bills.

Frequent bursts of acceleration and braking result in poorer fuel economy, said Mr Loh Chee Seng, a sales manager at ExxonMobil.

Underinflated tyres also cause fuel to be wasted, he said.

But Mr Lee insists he maintains a fairly constant speed when driving and keeps his tyres well-inflated.

Elgin Toh, newsroom intern

Fill up in the morning for more petrol. True or False?

There is nothing like a petrol price hike to increase the number of urban myths on how to save fuel. The New Paper on Sunday checks out these claims and asks the experts.

Myth 1: Petrol expands in hot weather, so fill up in the cooler early morning.

Finding: False

A spokesman for Chevron, which operates Caltex stations, says there is no difference in the amount of petrol you get whether you refuel in the day or night. This is because there is not much temperature variation in the air or in the fuel being dispensed, especially in a country like Singapore.

Any vaporisation that might occur would be a very small amount and the effect on the amount of petrol pumped would be negligible.

Myth 2: When filling up, do not squeeze the trigger fully and pump in 'fast' mode.

Finding: True

If you are pumping at a faster rate, some of the liquid that goes to your tank becomes vapour, which is sucked back into the underground storage tank, giving you less fuel.

This is a concern if the service stations are installed with vapour recovery systems which prevent petrol vapours from escaping to the air.

But not all stations use this. For instance, Caltex says its network in Singapore does not carry the system.

No matter the speed of the pump, there is always vapour loss to the surroundings.

However, the carbon canister in the fuel tank is able to capture some of the vapour during dispensing or normal operation, and it will be burnt off in the engine.

Myth 3: Fill up when your tank is half-full. The larger space in a near-empty tank could lead to higher petrol fume loss.

Finding: False

Again, the carbon canister located in the fuel tank is able to capture some of this vapour.

Myth 4: Overfilling your tank will result in the petrol flowing back into the pump.

Finding: False

The mechanism that allows petrol to flow back is called a return valve and they prevent harmful gas vapours from being released into the air.

They are installed in some countries such as the United States but the pumps here are not fitted with them.

Zaihan Mohamed Yusof

DRIVE SMART, SAVE MONEY

Regardless of what car you drive, good driving habits will help keep fuel consumption (and petrol bills) down. Here are some suggestions:

It's not a competition:

Don't weave in and out of traffic. Driving aggressively often means sudden acceleration and braking, which wastes petrol and will make you unpopular with other road users.

Too fast, bill furious:

Keep to the speed limit. While different cars have different speeds at which they are the most fuel-efficient, it is a good idea not to drive too fast. It will be safer too.

Get in tune:

Check the engine and air filters regularly. A properly tuned engine and clean air filters will leave you and your car purring with delight.

Pump them up:

Make sure the tyres are properly inflated. This also includes checking for both under-inflation and over-inflation.

Don't idle:

Waiting for someone? Consider turning off the engine if it is going to be more than a five-minute wait.

Lose weight:

Are you carting junk around in your boot? Lose it. Carrying extra weight just means you burn more petrol lugging it around.