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My 2002 Oldsmobile Intrigue goes through a litre of oil about every 10 days. There are no visible leaks and there is no blue smoke. Any ideas? – Patricia

You don't say how much the car is used or how much mileage it has accumulated. These two factors are critical in addressing the problem.

Does the engine have 15,000 or 150,000 kilometres on it? Do you drive 1,500 kilometres every 10 days or 15,000? It is not uncommon for a new engine to use half a litre of oil in 3,000-5,000 kilometres while others use none at all.

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Production tolerances are the main reason for the difference. If, for example, the acceptable range of tolerance is 0.05-mm to 0.1-mm, the engine with the larger gap will consume more oil or let more slip past (these numbers are for explanatory purposes only). As engines wear, the tolerances between parts increases, which in turn means increased consumption. Using a litre of oil every 1,500 kilometres is not unusual for a high-mileage engine.

In many cases, the head gasket has developed a leak. At that rate you might not notice anything in the exhaust. If oil consumption is excessive, it will likely create other problems such as fouled spark plugs, sensors and catalytic converter, which will in turn cause the engine to run rough and likely use more gas than normal.

The quickest way to see whether the consumption has reached such levels would be an emission check; have a qualified technician evaluate the exhaust gasses.

A compression check may not identify the problem if the oil is getting past the valve guides or piston rings.

As for leaks, you may not have noticed evidence of an oil leak on the driveway or garage floor, but there might still be a leak that is being burned off by a hot engine or exhaust system. Sources of this type or leak may be worn or broken gaskets – oil pan, valve cover, etc.

If it is a high-mileage engine that is getting plenty of use you might consider switching to special oils formulated for this purpose. They will not eliminate the problem but may slow down consumption. You could also try switching to a slightly higher viscosity or thicker oil.

The decision to do something further about the problem will depend on the value of the vehicle and your budget.

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