My BMW 5-series is approaching its 10th year. It revs up to 3,000rpm and remains buttery-smooth. But on the rare occasion when I rev it near 5,000rpm, I notice white fumes spewing from the exhaust and detect a loss in power. Is there a problem I should be worried about? I intend to extend the car's certificate of entitlement (COE).
First of all, your car has done pretty well, considering it is nearly 10 years old and still runs smoothly.
The cause of white smoke is most likely weak or worn oil-control rings on the pistons. This is not unusual nor is it an irreparable condition.
Since you intend to renew the COE, it might be worth your while to do an engine overhaul to replace the piston rings. If that is not feasible - as some piston and rings are sold as a set - then you will have to replace the pistons.
Make sure to have the cylinder walls inspected to ensure that there are no deep scratches that would require machining to remove.
The white smoke is attributable to blow-by, which is oil seeping past the piston rings. During combustion, the oil will burn, producing the white, sometimes slightly bluish smoke.
If the fuel-air mixture is contaminated with engine oil, you will not get the best performance from your car. That will lead to increased fuel consumption as well.
Try to have it fixed sooner than later, especially if you intend to keep the car running smoothly for another 10 years.