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"Regardless of the vehicle manufacturer, we have noticed white smoke being emitted immediately after an engine oil change. What could be the possible reason for this?"
White smoke most likely would indicate that water or coolant is getting into the combustion chamber or exhaust port. This can occur if coolant is leaking into the head. It could also be as simple as water entering the exhaust or carburetor after the engine was pressure-washed.
On the other hand, if the smoke is a bluish white, oil could be bypassing the rings on the piston or valve seals and being burnt in the combustion chamber. It is difficult to determine the exact cause without more information, but following are a few common scenarios.
In the case of bluish white smoke, the sump may have been overfilled with oil, and the excess oil is being dragged up the cylinder wall and into the combustion chamber by the overpressurizing of the crankcase. Smoke could also be emitted if the new oil used is not according to the original equipment manufacturer’s specifications. If the oil is not the correct type or viscosity, it could also bypass the rings on the piston or valve seals and end up in the combustion chamber.
Another cause of the smoke could be that the oil originally in the engine was a mineral oil but was replaced with a synthetic oil, which has a greater cleaning effect on varnish and soot deposits. Once the deposits have been washed away, the tolerances in the top end of the motor can open up, giving the oil pathways it never had before with the varnish and soot deposits in place. This is a very common scenario in older vehicles with higher mileage. However, this would probably not happen right after an oil change. It might take up to a few days for this to occur.
What can happen with older vehicles is that the person changing the oil will think the right thing to do is to switch to a synthetic base oil instead of the regular mineral base oil that has been used for the life of the vehicle. Once the new oil enters the engine and starts removing soot and varnish deposits from the valves and cylinders, it may lead to using (burning) more oil and smoke emitting from the vehicle.