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Over many decades, there has been an apparently never ending debate among lubrication experts as to the influence of crankcase lubricant on engine noise, in which opinions often substitute facts, and no consensus has been reached so far. This strange situation – best described by a famous phrase “a little knowledge is a dangerous thing” - is about to change as Noise, Vibration, and Harshness (NHV) aspects are getting increased attention from carmakers, motivating more fundamental research efforts. In recent years, acoustic emission measurements have become a routine tool for condition monitoring, and a number of studies have been carried out to apply this technique in order to investigate the influence of different factors on the noise level of car engines. Furthermore, since today’s customers are a lot more demanding to the car interior sound comfort, numerous psychoacoustic experiments have also been conducted to analyze different categories of unwanted sounds including rattling, creaking, squeaking and switch sounds.

These studies prove conclusively that the engine noise remains one of the decisive factors affecting driver’s and passengers’ comfort and their perception of car quality. The car interior noise always increases with the engine speed, for instance, when accelerating rapidly. It can be pleasing or irritating: The silky smooth baritone of a naturally aspirated V8 is perceived to be more pleasant than the scream of a boosted i4 motor. However, at motorway cruising speeds, wheel and wind noise becomes dominant. Lacking any well defined technical quantifiers of “pleasure” and “irritation”, lubricant manufacturers often resort to using an obscure term “feel factor” in order to describe the effect of lubricant of engine noise and its subjective perception by driver and passengers. There are several factors contributing to the acoustic emission spectrum, such as valves opening and closing, especially when hydraulic lifters are used, fuel combustion, piston slap, roller bearings used for supporting camshafts and balancing shafts in some engines, oil pump, water pump, generator, exhaust, fan, etc. These sources may interfere with each other, as well as with vibrations due to accelerating and decelerating masses (valves, lifters, pistons, connecting rods, crankshaft, etc.), producing a unique acoustic signature, including multiple resonant frequencies and overtones.

FIGURE 2 / Acoustic spectrum of common car interior noises. Courtesy of Kang-Duck Ih, Hyundai Motor Group, and Youngkey K. Kim, SM Instruments Co., Ltd.

The result you should experience yourself: BIZOL G+ motor oils do indeed make your engine run more quietly, effectively suppressing the most irritating high frequency noise emission. BIZOL G+ oils also provide superior engine protection and driver experience in urban driving, where engine noise is more intruding than wind or wheel noise you experience on highway (the latter is not affected by lubricant, anyway).