Oil changes are by far the most common service performed on vehicles in Canada. Customers pay quick lube facilities, private garages and dealer maintenance centres well over a billion dollars a year for the service. But a CBC investigation finds many of us may be changing our oil far more often than automakers require.

Marketplace went undercover at six dealerships in the Greater Toronto Area and received similar advice at four of them: Change the car's oil more often than what's recommended in the owner's manual.

"The people who built the car and engineered it and assembled it, all their knowledge is in that book, and that is king," says expert mechanic Mark Whinton. "It overrides anything a dealer can tell you."

As engines and oils improve, automakers have substantially increased the amount of time or distance that can elapse between oil changes.

Hidden camera video reveals dealership service advisors recommending oil changes far earlier than the manufacturer recommends in the owner's manual 0:46

Many vehicles built in the past five years only require an oil change once a year, to a maximum of 16,000 kilometres. And yet, when CBC Marketplace approached dealership service centres to ask about vehicles on that schedule, service advisers — recorded on hidden camera — offered different advice.

"You should be changing it minimum every six months," an adviser at a Fiat dealership said. The advice was similar at a Chrysler dealership: "Do not exceed 10,000 kilometres or six months." A Jeep dealership suggested even more often: "We recommend every 5,000 kilometres or three months."

'It's nonsense'

When challenged on why they were recommending service far more often than the vehicle manufacturer proposes in the owner's manual, the advisers offered reasons like, "Oil starts to break down after about 5,000 kilometres," and Canada's "extreme weather" requires the schedule be accelerated.

"This is 25-year-old advice," Whinton says. "Whatever the service adviser tells you, it's made up, it's nonsense. Cars run at a certain temperature. They're all thermostatically controlled … so this argument no longer holds water really about, 'Oh, you know, it's cold outside.'"

Most modern vehicles have oil-life indicators. The device tracks the requirements laid out by the manufacturer. Some monitor the oil itself, while others track the time and distance since the last change. Certain manufacturers do say extreme driving conditions, such as towing, may cause a dashboard oil change indicator to illuminate sooner than scheduled.

Mechanic Mark Whinton says car owners should read their manual rather than listen to their dealership's service adviser. (CBC)

So why would dealerships recommend a more frequent schedule?

Lucas Leung, a former service adviser at five different dealerships, suggests money may be a factor. He says dealerships want customers coming in frequently to upsell them on other services.

"It's an opportunity for us to find things on the vehicle that may be wrong."

Testing the oil

CBC inquired about the maintenance requirements for a 2013 Jeep Wrangler at a dealership. The vehicle had not had an oil change for eight months but had driven only about 1,000 kilometres. The owner's manual recommends following the indicator to a maximum of 12 months or 16,000 kilometres.

The dealership recommended an oil change every three months or 5,000 kilometres.

So Marketplace had the engine oil tested at Fluid Life, a business that specializes in oil analysis for light and heavy vehicles. District sales manager Mark Shierman found the "oil results look really good, actually." Though the oil was discoloured, Shierman said it still had life.

"I would not change this oil right now."

Marketplace enlists a company called Fluid Life to test oil from a Jeep Wrangler that a dealership service adviser said needed to be changed. (CBC)

Marketplace contacted the four dealerships whose service advisers provided advice that differed from what's found in the owner's manuals.

The Dodge and Fiat dealerships stood by their staff's advice. They argued the manufacturer's schedule is just "the minimum maintenance required," and that the cars should be brought in more frequently for "peace of mind."

The Ford dealership went against its service adviser, conceding that drivers should, in fact, be following their owner's manual.

The Jeep dealership, which recommended oil changes every three months, declined to comment.

Mechanic Mark Whinton says before heading to any garage, car owners should check the owner's manual.

"If anything was to happen to your car … you could rely on that document as the definitive source of information for what you're supposed to do to maintain your car."