This paper presents a new approach for the allowable limit of oil aeration rate not to be detrimental to the engine bearing reliability. This approach is based on the measurement of minimum oil film thicknesses(MOFTs) of bearings and crankshaft temperatures according to the change of oil aeration rate. Oil is liable to be aerated under high speed conering condition and it results in. the main gallezy oil pressure drop. This level of oil aeration is duplicated in an engine dyno test by the use of a special air injection device and monitored with on-line aeration measurement system. Bearing reliability is evaluated by the measured results of MOFTs in bearings and the surface temperatures of crankshaft, and especially linkage system was used for measuring MOFT in a connecting rod bearing. Consequently, oil aeration rate lower than 30% (under the any main gallezy oil pressure) is verified to be allowable to maintain oil film in a bearing. Based on this guideline, the problem of connecting rod bearing failure occurred during high speed cornering of a vehicle can be improved by the modification of oil pan and strainer.