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Q: Heavy exhaust smoke on the right side at cold start which disappears after some 15 minutes of motor running

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At the same time hear a piston knock also at the right side which gradually will also disappear. What could be wrong and how to repair. Thanks for your answer

My car has 30000 miles.
My car has an automatic transmission.

A: Hello. From what you describe, it would app...

Hello. From what you describe, it would appear that your vehicle may be experiencing more than one issue. A common cause for smoke that goes away after a short period of driving is an oil leak.

If one of the engine’s gaskets leaks oil onto the exhaust manifolds it may cause smoke as a result of the oil burning up once the manifold gets hot. The smoke will go away once all of the oil residue is burned up, and will return once more oil has collected on the manifold as a result of the leak.

I would carefully examine the exhaust manifold as well as cylinder head on the right side of the engine for any traces of oil. If you are hearing a piston knock sound that may be a sign of mechanical issues. Usually a knock will be produced as a result of worn pistons, cylinder walls, or bearings, or if the oil is low.

Continuing to drive the vehicle with the engine producing a knocking sound could potentially lead to serious engine damage. I would check the oil to make sure that it is not low, which may be possible if there is a leak. If you’d like to have an expert diagnose the knocking sound, consider YourMechanic, as a certified technician can come to your car’s location to pinpoint the problem and advise you on repairs.

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