The performance of a mechanical filter is an implicit function of many variables pertinent to fluid condition, flow variables, filter element condition and operational parameters. This paper presents the details and results of a parametric study that examined the effect of oil temperature, contamination level and flow rate on the performance of a hydraulic filter through laboratory experiments. A 5 µm rated commercial filter with glass fiber made element that had an effective surface area of 0.154 m2 through 57 pleats was used to filter VG32 hydraulic oil. The filtrate was supplied with the contaminant of ISO medium test dust at four gravimetric levels - 2, 5, 8 and 10 mg/L of oil. The tests were conducted at the flow rates of 40 and 120 L/min for different oil viscosities, corresponding to the temperatures of 30, 40, 50 and 60o C. As the temperature increases, the oil viscosity decreases due to weakened cohesive forces, which leads to increased filtration rates and hence more time to build the pressure, upstream of the element. On the other hand, the pressure on upstream of filter bed builds up at higher rate when the filtrate has higher level of contamination loading. An extensive investigation on the effect of flow variables and oil condition parameters on the pressure drop across the element would therefore give a better knowledge about filter element lifetime.