Vanguard BIG BLOCK M540000, Repair Manual, Page: 41 / 168

Oil Pressure
Test Oil Pressure Switch
2 types of oil pressure switches may be used on your engine,
depending on the model, trim and type. The first type is a
Normally-closed oil pressure switch. With the engine OFF,
the contacts within the switch are CLOSED, completing a
circuit. When oil pressure is built up as the engine starts, the
switch opens and the ground contact is interrupted. Normally-
closed oil pressure switches are used to activate items such
as an alarm or warning light if the oil pressure drops to a
predetermined PSI level.
The second type is a Normally-open oil pressure switch.
With the engine OFF, the contacts within the switch are
OPEN, interrupting the circuit. When oil pressure is built up
as the engine starts, the switch closes the ground contact,
completing the circuit. Normally-open oil pressure switches
may be used to activate items such as an hour meter when
the oil pressure reaches a predetermined PSI level.
It is important to determine the type AND specification of
the oil pressure switch on your engine BEFORE testing.
Review the Illustrated Parts List to determine the correct part
specification.
1. Obtain a digital multimeter. Set meter to test for
continuity. See Special Tool List .
2. Remove oil pressure switch from engine. See SECTION
4 - REMOVE EXTERNAL ASSEMBLIES - Oil Pressure
Switch .
3. Connect on tester lead to the oil pressure switch terminal
and the other lead to the metal body of the switch. If
equipped with a Normally-closed oil pressure switch,
the tester should indicate CONTINUITY when no
pressure is applied to the switch. If equipped with a
Normally-open oil pressure switch, the tester should
indicate OPEN when no pressure is applied to the
switch. Replace the switch if the test results are not to
specification.
4. If the oil pressure switch is within specification but the
warning light remains ON, proceed to oil pressure test.
Test Oil Pressure
The engine oil level must be between the LOW and FULL
mark on the dipstick. If the oil level is low, check for leaks and
add oil to FULL mark.
1. Obtain oil pressure gauge.
2. Remove the oil pressure switch or the 1/8" NPTF plug on
the engine crankcase.
3. Install the oil pressure gauge. See gauge instructions for
proper procedures and steps.
4. Start the engine. Allow the engine to run for
approximately 5 minutes .
5. Check the oil pressure at 3000 RPM . Oil pressure should
read between 10-50 PSI (0.7-3.5 Bar) .
Oil Pressure Troubleshooting Guide
Engine RPM too low
Wrong viscosity or diluted oil
Low oil level
Broken pressure relief spring
Missing pressure relief plunger
Worn bearings
Low Oil Pressure
Damaged or defective oil pump
Wrong viscosity oil
Plugged oil passages
High Oil Pressure
Stuck pressure relief plunger
Starter Motor
Conditions Affecting Starter Motor Performance
1. Bound or seized starter motor bearings.
2. A shorted, open or grounded armature.
a. Shorted armature (wire insulation worn and wires
touching one another) will be indicated by LOW or
NO RPM .
b. Open armature (wire broken) will be indicated by
LOW or NO RPM and excessive current draw.
c. Grounded armature (wire insulation worn and
wire touching armature lamination or shaft) will be
indicated by excessive current draw and NO RPM .
3. A defective starter motor switch.
4. Broken, damaged or weak magnets.
5. Dirty or binding starter drive.
6. Defective or damaged wires, cables and terminal
connections.
a. High resistance on either the positive or negative
side of the starter motor can reduce the current to
the starter motor. This will cause LOW cranking
speeds.
b. High resistance on the the starter motor solenoid
control circuit reduces the current to the solenoid
switch. This can prevent the starter from operating.
c. Excessive voltage loss, from defective or damaged
wires, cables and connections will affect starter
motor performance.
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