This service is recommended as a preventative maintenance service but is also recommended if you have valve train noise, poor fuel efficiany, loss of power, slow response or excessive smoking. The BG products used will remove oil sludge and varnish and restore compression. The chemicals used are harmless to oil pumps, seals and gaskets. What you may notice after the cleaning is that there is lower tailpipe emmisions, reduced oil consumption and also improved overall power and engine efficiency.