What is Walnut Blasting?
Walnut blasting is the process of blasting pressurized, crushed walnut shells onto the intake valves and in the cylinder on direct injection engines. This procedure is designed to remove carbon deposits which accumulate over time from blow-by gases, carbonized fuel, and oil on the intake valves and intake ports of the cylinder head. When the valves become heavily carbonated, the engine may exhibit symptoms such as misfire, rough idle, and lack of power, which is a result of the intake valves not being able to close properly.
With a clean running engine, power will be restored with a more responsive throttle and allow for an increase in fuel economy. We recommend to have this service performed every 30,000 miles on your BMW equipped with N54 and N55 engines, available on the 135i, 335i and 535i. This service is more involved on V8 motors such as N63 and diesel motors M57, N57 which requires a more thorough and labor intensive chemical cleaning.
Although carbon buildup is unavoidable, preventive measures can be taken to reduce it. Oil changes performed regularly of every 5,000 miles can reduce the amount of carbon buildup. We certainly don't agree with BMW's oil service interval of 10,000 - 15,000 miles. The spark plugs should also be replaced every 45,000 miles to reduce the amount of unburned fuel which will allow less carbon to stick to the intake vales.