An electric vehicle is seen parked at a recharging bay in central London, March 21. Britain raised taxes on the most polluting cars on last Wednesday, in an effort to entice drivers away from gas-guzzling vehicles which damage the environment. - REUTERS

DETROIT (AP):

Most major automakers agree: The adage that you should change your car's oil every 3,000 miles (5,000 kilometres) is outdated, and even 5,000 miles (8,000 kilometres) may be too often.

Ford Motor Co. became the latest manufacturer to extend its oil life guidelines, making public that it is raising the recommended oil change interval from 5,000 miles (8,000 kilometres) to 7,500 miles (12,000 kilometres) on its newly redesigned 2007 models and all subsequent redesigned or new models.

The company, like many other manufacturers, said last Tuesday that higher oil quality standards and new engine designs were responsible for the change, which affects vehicles driven under normal conditions.

More robust oils

"The oils have advanced a lot since the days when 3,000 miles were the typical oil drains," said Dennis Bachelder, senior engineer for the American Petroleum Institute, an industry organisation that sets quality standards. "They're certainly more robust than the oils of 10, 15 years ago."

These days, motor oils start with a higher-quality base oil than in the past, and they have more antioxidants that make lubricating properties last longer and other additives that keep deposits from forming on engines, Bachelder said.

Some manufacturers, such as Honda Motor Co. and General Motors Corp., have stopped making recommendations on all or most of their models, instead relying on sensors that measure oil temperature extremes and engine revolutions over time to calculate oil life and tell drivers when to get the lubricant changed. Oil can lose its lubricating properties if it runs at too low or too high of a temperature.

Peter Lord, executive director of GM's service operations, said oil can last 12,000 miles (19,000 kilometres) or even more for many drivers who do not run their vehicles in extreme heat or cold or tow heavy loads. "It really does depend on the individual customer and how they've used the vehicle," he said.

Ford said it has found that its customers like a set mileage for service rather than wait for a sensor to tell them what to do. For those who do not believe the sensors, Lord says GM has reams of data showing that they are reliable, and they notify drivers far in advance of when a change is necessary.

"We are absolutely confident of the technology. We back it with a 100,000 mile powertrain warranty now, so there's no doubt in our mind that this technology works," he said.

The longer oil life can save customers money. Ford estimates that drivers would save US$600 (?451) over a five-year period by going from 5,000 miles to 7,500 between oil changes.

"From an environmental perspective we can save an enormous amount of oil," Lord said. "There's no point in wasting precious oil changing it prematurely. And we don't have to dispose of so much waste oil, either."

Controversial

When to change oil isnot without controversy, though.

Toyota Motor Corp. reduced its change interval from 7,500 miles to 5,000 in 2004 in part because it found that more drivers ran their vehicles under severe stop-and-start and short trip conditions that cause oil to deteriorate more quickly, said company spokesman Bill Kwong.

Toyota also had an oil sludge build-up problem on less than 1 percent of its 1997-2002 model year vehicles, Kwong said. Changing the oil more frequently prevents the sludge problem, which he said was caused by owners going more than 7,500 miles before changing oil.

The company lengthened warranty coverage on the affected engines to handle the problem, even before some owners filed a class action lawsuit, Kwong said.

Nissan Motor Co. recommends changing oil in its Nissan and Infiniti vehicles every 7,500 miles or six months - unless the vehicle is used mainly for towing, trips of 5 miles or less in normal temperatures, 10 miles or less in freezing temperatures, stop-and-go driving in hot weather or low-speed driving for long distances, in which cases the oil should be changed every 3,750 miles or three months, spokeswoman Katherine Zachary said.