The engine lubrication system is of the force-feed
type. The oil is supplied under full pressure to the
crankshaft, connecting rods, valve lash adjusters,
and cam phasing system. A controlled volume of
oil is supplied to the camshaft and valve rocker
arms. Gravity flow or splash lubricates all other
parts. The engine oil is stored in the oil pan, which
is filled through a fill cap in the camshaft cover. A
removable oil level indicator, on the right side of
the engine block, is provided to check the oil level.
The oil pump is located in the engine front cover
and is driven by the crankshaft. It is a gerotor-style
pump, which is a combination of a gear, and a
rotor pump. It is connected by a passage in the
cylinder block to an oil screen and pipe assembly.

The screen is submerged in the oil supply and has
ample volume for all operating conditions. Oil is
drawn into the pump through the screen and pipe
assembly, and a passage in the crankcase,
connecting to the passages in the engine front
cover. Oil is discarged from the oil pump to the oil
filter. The oil pressure relief valve limits the oil
pressure. The oil filter bypass valve opens when
the oil filter is restricted to approximately 68.95
kPa (10 psi) of pressure difference between the oil
filter inlet and discharge.
4.2L Engine Oiling System Description And Operation

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The oil will then bypass the oil filter and channel unfiltered oil
directly to the main oil galleries of the engine. A full-flow oil filter
is mounted to the oil filter adapter on the lower right front side of
the engine. The main oil galleries run the full length of the
engine block and cut into the valve lash adjuster holes to supply
oil at full pressure to the valve lash adjusters.

Holes are drilled from the crankshaft bearings to the main oil
gallery. Oil is transferred from the crankshaft bearings to the
connecting rod bearings through holes drilled in the crankshaft.
Pistons, piston pins, and cylinder walls are lubricated by oil
splash from the crankshaft and connecting rods. The camshafts
and valve rocker arms are supplied with oil from the oil
passages drilled into the camshaft mounting areas.