Dodge ram truck 3500 1996 Service Manual page 312

7 - 28 COOLING SYSTEM
BR
DIAGNOSIS AND TESTING (Continued)
Fig, 88 Leak Detection Using Black Light—Typical
WARNING: WITH COOLING SYSTEM PRESSURE
T E S T E R TOOL INSTALLED ON RADIATOR, DO NOT
ALLOW P R E S S U R E TO E X C E E D 110 KPA (20 PSI).
P R E S S U R E WILL BUILD UP QUICKLY IF A COM­
BUSTION LEAK IS PRESENT. TO R E L E A S E P R E S ­
S U R E , ROCK T E S T E R FROM SIDE TO SIDE. WHEN
REMOVING T E S T E R , DO NOT TURN T E S T E R MORE
THAN 1/2 TURN IF SYSTEM IS UNDER P R E S S U R E .
Operate engine without pressure cap on radiator
until thermostat opens. Attach a pressure tester to
filler neck. I f pressure builds up quickly it indicates a
combustion leak exists. This is usually the result of a
cylinder head gasket leak or crack in engine. Repair
as necessary.
If there is not an immediate pressure increase,
pump the pressure tester. Do this until indicated
pressure is within system range of 110 kPa (16 psi).
Fluctuation of gauge pointer indicates compression or
combustion leakage into cooling system.
Because the vehicle is equipped with a catalytic
converter, do not remove spark plug cables or short
out cylinders (non-diesel engines) to isolate compres­
sion leak.
If the needle on dial of pressure tester does not
fluctuate, race engine a few times to check for an
abnormal amount of coolant or steam. This would be
emitting from exhaust pipe. Coolant or steam from
exhaust pipe may indicate a faulty cylinder head gas­
ket, cracked engine cylinder block or cylinder head.
A convenient check for exhaust gas leakage into
cooling system is provided by a commercially avail­
able Block Leak Check tool. Follow manufacturers
instructions when using this product.
COMBUSTION LEAKAGE TEST—WITHOUT
PRESSURE TESTER
DO NOT WASTE reusable coolant. I f solution is
clean, drain coolant into a clean container for reuse.
WARNING: DO NOT REMOVE CYLINDER B L O C K
DRAIN P L U G S OR L O O S E N RADIATOR DRAIN-
C O C K WITH S Y S T E M HOT AND UNDER P R E S S U R E .
SERIOUS BURNS FROM COOLANT CAN OCCUR.
Drain sufficient coolant to allow thermostat
removal. Refer to Thermostat Replacement. Discon­
nect water pump drive belt.
Add coolant to radiator to bring level to within 6.3
mm (1/4 in) of top of thermostat housing.
CAUTION: Avoid overheating. Do not operate
engine for an excessive period of time. Open drain-
cock immediately after test to eliminate boil over.
Start engine and accelerate rapidly three times, to
approximately 3000 rpm (2000 rpm for diesel) while
observing coolant. I f internal engine combustion
gases are leaking into cooling system, bubbles will
appear in coolant. I f bubbles do not appear, internal
combustion gas leakage is not present.
VISCOUS FAN DRIVE
NOISE
NOTE: It is normal for fan noise to be louder (roar­
ing) when:
• The underhood temperature is above the engage­
ment point for the viscous drive coupling. This may
occur when ambient (outside air temperature) is very
high.
• Engine loads and temperatures are high such as
when towing a trailer.
• Cool silicone fluid within the fan drive unit is
being redistributed back to its normal disengaged
(warm) position. This can occur during the first 15
seconds to one minute after engine start-up on a cold
engine.
LEAKS
Viscous fan drive operation is not affected by small
oil stains near the drive bearing. I f leakage appears
excessive, replace the fan drive unit.
TESTING
If the fan assembly free-wheels without drag (the
fan blades will revolve more than five turns when