Jeep 1997 Grand Cherokee Service Manual page 232

7 - 4 COOLING SYSTEM
DESCRIPTION AND OPERATION (Continued)
ACCESSORY DRIVE BELT TENSION
Correct drive belt tension is required to ensure
optimum performance of the belt driven engine acces-
sories. If specified tension is not maintained, belt
slippage may cause; engine overheating, lack of
power steering assist, loss of air conditioning capac-
ity, reduced generator output rate, and greatly
reduced belt life.
4.0L ENGINE
Belt tension is adjusted at the power steering
pump bracket and idler pulley assemly. There are dif-
ferent types of adjustment gauges for checking either
a serpentine or a V-type belt. Refer to the instruc-
tions supplied with the gauge. Use the correct gauge
when checking belt tension. Place gauge in the mid-
dle of the section of belt being tested (between two
pulleys) to check tension. Do not allow the gauge (or
gauge adapter) to contact anything but the belt.
5.2/5.9L ENGINES
It is not necessary to adjust belt tension on the 5.2/
5.9L engines. These engines are equipped with an
automatic belt tensioner. The tensioner maintains
correct belt tension at all times. Due to use of this
belt tensioner, do not attempt to use a belt tension
gauge on 5.2/5.9L engines.
ENGINE BLOCK HEATER
An optional engine block heater (Fig. 5) (Fig. 6)is
available with for all models. The heater is equipped
with a power cord. The cord is attached to an engine
compartment component with tie-straps. The heater
warms the engine providing easier engine starting
and faster warm-up in low temperatures. The heater
is mounted in a core hole of the engine cylinder block
in place of a freeze plug with the heating element
immersed in engine coolant. Connect power cord to a
grounded 110-120 volt AC electrical outlet with a
grounded, three wire extension cord.
WARNING: DO NOT OPERATE ENGINE UNLESS
BLOCK HEATER CORD HAS BEEN DISCONNECTED
FROM POWER SOURCE AND SECURED IN PLACE.
THE POWER CORD MUST BE SECURED IN ITS
RETAINING CLIPS AND ROUTED AWAY FROM
EXHAUST MANIFOLDS AND MOVING PARTS.
THERMOSTAT
A pellet-type thermostat controls the operating
temperature of the engine by controlling the amount
of coolant flow to the radiator. On all engines the
thermostat is closed below 195°F (90°C). Above this
temperature, coolant is allowed to flow to the radia-
tor. This provides quick engine warm up and overall
temperature control.
BLOCK ENGINE LOWER POWER C ORD POWER CORD LOCA- TION HEATER BLOCK
Fig. 5 Block Heater—4.0L 6-Cyl. Engine
Fig. 6 Block Heater—5.2/5.9L V-8 Engines
An arrow, plus the word UP is stamped on the
front flange next to the air bleed. The words TO
RAD are stamped on one arm of the thermostat.
They indicate the proper installed position.
The same thermostat is used for winter and sum-
mer seasons. An engine should not be operated with-
out a thermostat, except for servicing or testing.
Operating without a thermostat causes other prob-
lems. These are: longer engine warmup time, unreli-
able warmup performance,
emissions and crankcase condensation. This conden-
sation can result in sludge formation.
CAUTION: Do not operate an engine without a
thermostat, except for servicing or testing.
BLOCK HEATER
ZG
increased exhaust