For developing automotive industry, one of the focusing point is reduction of engine friction level to decrease both engine emissions and fuel consumption. Important part of researchers have focused on cold engine start period, which has higher friction loses. Shorter warm up period and faster heating of engine oil help to provide better engine performance. Not only warm up time but also better cool down period after engine stops, dramatically effects engine efficiency. If oil temperature stays hot for longer time during the vehicle key-off duration, it brings an important advantageous at the next start. Main purpose of this study is to investigate oil temperature changes depending on the design parameters of the oil pan. This investigation is done for oil warm up and cool down periods by mathematical model, which is validated for 2.0 L and 4 cylinders diesel engine. Design improvement combinations against base steel oil pan has been examined throughly in terms of oil temperature changes, warm up and cool down time, fictional loses and weight reduction opportunity. As a result, 5 mm thickness plastic oil pan with windage tray application is the best solution option since it brings both 12.5 % friction decreasing in cold start after 2 hours key-off duration, and 43 % weight reduction.