Lubricating Oil Pump
The engine uses a gerotor type lubricating oil pump (1). The machined cavity in the block is the same for all engines.
A wider gerotor is used in the six cylinder engine to increase the lubricating pump capacity. Consequently, the 4 cylinder and 6 cylinder lubricating pumps are not interchangeable.
Pressure Regulating Valve
The pressure regulating valve (2) is designed to keep the lubricating oil pressure from exceeding 449 kPa [65 psi].
When the lubricating oil pressure from the pump is greater than 499 kPa [65 psi], the valve opens uncovering the
dump port so part of the lubricating oil is routed to the oil pan. The minimum lubricating oil pressure limit is the
same for the four cylinder and the six cylinder engine. Because of manufacturing tolerances of the components
and the oil passages, the lubricating oil pressure can differ as much as 69 kPa [10 psi] between engines.
Lubricating Oil Coolers
The engines use full flow, plate type oil coolers (3). The oil flows through a cast passage in the cooler cover and
through the element where it is cooled by engine coolant flowing past the plates of the element. The four cylinder
engine uses an element with five plates (A), the six cylinder uses an element with seven plates (B). Because of
the differences in plate restriction and oil pump capacities, the oil cooler components are not interchangeable
between the four cylinder and six cylinder engines. The use of incorrect components can cause high or low oil
temperature, varnish and sludge build up.
NOTE: Prior to 10/21/86 six cylinder engines were assembled with 9 plate oil cooler elements.
Lubricating Oil Filters
After the oil is cooled, it flows through the full flow oil filter (4). The filter for the six cylinder engine is longer than
the filter for the four cylinder engine.
Lubricating Oil Filter Bypass Valve
The lubricating oil cooler cover contains a bypass valve (5) that will let the lubricating oil flow bypass a plugged
filter. The valve is designed to open when the pressure drop across the filter is more than 138 kPa [20 psi], as with
a plugged filter, and lets the lubricating oil continue on through the engine. When a filter becomes plugged, an
oil pressure decrease of 60 kPa [10 psi] or less from the normal operating pressure can be observed on the vehicle
lubricating oil pressure gauge. This allows unfiltered oil into the engine. This condition should be avoided by
changing the filter at each oil drain interval as described in the Operation and Maintenance Manual, Bulletin No.
3810205-10.