Pressure system of lubrication.

The pressure system is used almost universally in modern car engines. The splash system though cheaper, is not suitable for automobile engines because of the absence of positive lubrication. 

In the pressure system, an oil pump takes the oil from the pump through a strainer and delivers it through a filter to the main oil gallery at a pressure of 2-4 kg/cm². There is one main gallery in the case of inline engines, whereas v engines use two main galleries or one main gallery and two valve-tapped galleries.

From the main gallery, the oil goes through the drilled passages to the main bearings, from where some of the oil after lubricating the main bearing falls back to the sump, some are splashed to lubricate cylinder walls while the rest goes through a hole to the crankpins from where a hole in the lubricating connecting rod web, leads it to the gudgeon pin. 

After lubricating the gudgeon pin bearings the oil falls back or effects ring lubrication. The oil that falls on the cylinder wall drains back into the oil pan and is recalculated through the lubricating system.

            For the camshaft and timing gears, lubricating oil is led through the separate oil line from the oil gallery through a pressure-reducing separate oil line from the oil gallery through a pressure-reducing valve. 

To lubricate the timing gearing and the sprocket chain, sometimes a directed oil jet is employed. The valve tappets are lubricated by connecting the main oil gallery to the tappet guide surfaces through drilled holes. In the case of the overhead valve mechanism, the rocker's arms are sometimes mounted on hollow shafts to feed oil for the lubrication of the rocker's arms.

In some other designs, the push rods are made hollow and the oil under pressure is made to flow up to provide lubrication of various parts of the valve train. The oil that seeps from the valve train as above is returned to the oil pan through drain holes, which are sometimes so placed that the oil drains on the camshaft and the timing gears to lubricate them.

During its circulation, the oil gains heat from various engine parts, which are given out to the sump walls. In some heavy-duty engines, a separate oil cooler is also employed.