Over the past decades, the automotive industry has made significant efforts to improve engine fuel economy by reducing mechanical friction in cold conditions. One of countermeasures is an improvement of warming up time by restricting coolant flow. Another way to reduce the friction is to optimize an oil pump function to provide minimum, but necessary and sufficient oil pressure to the lubrication system. Another challenge for the automotive industry is the reduction of exhaust emission. An oil dilution ratio by fuel and a particle number (PN) have been a recent concern. A piston surface temperature has negative impact to them. Appropriate piston cooling is an important technical issue while increasing power density of engines. In order to achieve these requirements in engines, a new type of oil pump with a function to vary the oil pressure depending on its demand was developed. An internal gear optimum pressure oil pump design was adopted first in the world. The new oil pump design provides lower mechanical friction, lower pressure pulsation and wider range of outlet pressure along with wider temperature range in comparison with existing designs. In addition, the oil circuit was re-constructed to maximize the effect of the optimum pressure pump. The new oil gallery was adopted only for the oil-jet, and the oil pressure sensor was settled near the devices of engine lubricant parts. The new oil pump achieved to control oil jet flow fully from complete shut-off to full flow without an oil switching valve, and resulted in the reduction of engine oil dilution by 50%. The fuel economy was also improved by 1.0% as the EPA combined fuel economy measurement.