Lexus SC300 / Lexus SC400. Service manual

A pressure feeding lubrication system has been adopted to supply oil to the moving parts of this engine. The

lubrication system consists of an oil pan, oil pump, oil filter and other external parts which supply oil to the moving
parts in the engine block. The oil circuit is shown in the illustration at the top of the previous page. Oil from the
oil pan is pumped up by the oil pump. After it passes through the oil filter, it is fed through the various oil holes
in the crankshaft and cylinder block. After passing through the cylinder block and performing its lubricating func-
tion, the oil is returned by gravity to the oil pan. A dipstick on the center left side of the cylinder block is provided
to check the oil level.

OIL PUMP

The oil pump pumps up oil from the oil pan and sends it under pressure to the various parts of the engine.

An oil strainer is mounted in front of the inlet to the oil pump. The oil pump itself is a trochoid type pump, inside
of which there is a drive rotor and a driven rotor. When the drive rotor rotates, the driven rotor rotates in the same
direction, and since the axis of the driven rotor shaft is different from the center of the driven rotor, the space
between the two rotors is changed as they rotate. Oil is drawn in when the space is wide and is discharged when
the space in narrow.

OIL PRESSURE REGULATOR

At high engine speeds, the engine oil supplied by the oil pump exceeds the capacity of the engine to utilize

it. For that reason, the oil pressure regulator works to prevent an oversupply of oil. During normal oil supply, a
coil spring and valve keep the bypass closed, but when too much oil is being fed, the pressure become extremely
high, overpowering the force of the spring and opening the valves. This allows the excess oil to flow through
the valve and return to the oil pump inlet.

OIL FILTER

The oil filter is a full flow type filter with a built–in paper filter element. Particles of metal from wear, airborne

dirt, carbon and other impurities can get into the oil during use and could cause accelerated wear or seizing if
allowed to circulate through the engine. The oil filter, integrated into the oil line, removes these impurities as the
oil passes through it. The filter is mounted outside the engine to simplify replacement of the filter element. A relief
valve is also included ahead of the filter element to relieve the high oil pressure in case the filter element be-
comes clogged with impurities. The relief valve opens when the oil pressure overpowers the force of the spring.
Oil passing through the relief valve by–passes the oil filter and flows directly into the main oil hole in the engine.

–

LUBRICATION SYSTEM

Precautions

LU–3

Lexus SC300 / Lexus SC400. Service manual - part 639