Jeep Cherokee 1999 Electronic Service Manual page 207

7 - 4 COOLING SYSTEM
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
Fig. 3 Reserve/Overflow Tank—With Right Hand
COOLING SYSTEM FANS
All m odels a r e equ ipped wit h a viscou s fa n . Th is
t h er m a l viscou s fa n dr ive is a t or qu e-a n d-t em per a -
t u r e-sen sit ive clu t ch u n it . It a u t om a t ica lly in cr ea ses
or decr ea ses fa n speed t o pr ovide pr oper en gin e cool-
in g. Veh icles wit h a 2.5L/4.0L en gin e wit h a ir con di-
t ion in g, or 4.0L wit h "m a x" coolin g a lso h a ve a n
a u xilia r y elect r ica l coolin g fa n .
F or in dividu a l descr ipt ion s or oper a t ion , r efer t o
Viscou s F a n Dr ive or E lect r ic Coolin g F a n in t h is
gr ou p.
ACCESSORY DRIVE BELT TENSION
Bot h t h e 2.5L a n d 4.0L en gin es u se on e a ccessor y
dr ive belt . Cor r ect dr ive belt t en sion is r equ ir ed t o
en su r e opt im u m per for m a n ce of t h e belt dr iven
en gin e a ccessor ies. Th er e a r e differ en t t ypes of
a dju st m en t ga u ges for ch eckin g eit h er a P oly–V or a
con ven t ion a l V-t ype belt . Refer t o t h e in st r u ct ion s
su pplied wit h t h e ga u ge. Ma ke su r e t o u se a ga u ge
design ed specifica lly for ser pen t in e st yle belt s. P la ce
ga u ge in t h e m iddle of t h e sect ion of belt bein g t est ed
(bet ween t wo pu lleys) t o ch eck t en sion . Do n ot a llow
t h e ga u ge (or ga u ge a da pt er ) t o con t a ct a n yt h in g bu t
t h e belt .
F or belt t en sion specifica t ion s, r efer t o Specifica -
t ion s-Accessor y Dr ive Belt in t h is gr ou p.
BLOCK HEA TER
An opt ion a l en gin e block h ea t er is a va ila ble for a ll
m odels. Th e h ea t er is equ ipped wit h a power cor d.
Th e cor d is a t t a ch ed t o a n en gin e com pa r t m en t com -
Drive
pon en t wit h t ie-st r a ps. Th e h ea t er wa r m s t h e en gin e
pr ovidin g ea sier en gin e st a r t in g a n d fa st er wa r m -u p
in low t em per a t u r es. Th e h ea t er is m ou n t ed in a cor e
h ole of t h e en gin e cylin der block (in pla ce of a fr eeze
plu g) wit h t h e h ea t in g elem en t im m er sed in en gin e
coola n t . Con n ect t h e power cor d t o a gr ou n ded 110-
120 volt AC elect r ica l ou t let wit h a gr ou n ded, t h r ee-
wir e ext en sion cor d.
WARNING: DO NOT OPERATE ENGINE UNLESS
BLOCK HEATER CORD HAS BEEN DISCONNECTED
FROM POWER SOURCE AND SECURED IN PLACE.
B LOCK HEATER S P ECIF ICATION S
• 2.5L 4-Cylin der E n gin e: 115 Volt s 400 Wa t t s
• 4.0L 6-Cylin der E n gin e: 120 Volt s 600 Wa t t s
THERMOSTA T
A pellet -t ype t h er m ost a t con t r ols t h e oper a t in g
t em per a t u r e of t h e en gin e by con t r ollin g t h e a m ou n t
of coola n t flow t o t h e r a dia t or. On a ll en gin es t h e
t h er m ost a t is closed below 195°F (90°C). Above t h is
t em per a t u r e, coola n t is a llowed t o flow t o t h e r a dia -
t or. Th is pr ovides qu ick en gin e wa r m -u p a n d over a ll
t em per a t u r e con t r ol.
An a r r ow plu s t h e wor d U P is st a m ped on t h e
fr on t fla n ge n ext t o t h e a ir bleed. Th e wor ds TO
RAD a r e st a m ped on on e a r m of t h e t h er m ost a t .
Th ey in dica t e t h e pr oper in st a lled posit ion .
Th e sa m e t h er m ost a t is u sed for win t er a n d su m -
m er sea son s. An en gin e sh ou ld n ot be oper a t ed wit h -
ou t a t h er m ost a t , except for ser vicin g or t est in g.
Oper a t in g wit h ou t a t h er m ost a t ca u ses ot h er pr ob-
lem s. Th ese a r e: lon ger en gin e wa r m -u p t im e, u n r e-
lia ble wa r m -u p per for m a n ce,
em ission s a n d cr a n kca se con den sa t ion . Th is con den -
sa t ion ca n r esu lt in slu dge for m a t ion .
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
COOLANT PERFORMANCE
ETHYLENE-GL YCOL MIXTURES
Th e r equ ir ed et h ylen e-glycol (a n t ifr eeze) a n d wa t er
m ixt u r e depen ds u pon t h e clim a t e a n d veh icle oper-
a t in g con dit ion s. Th e r ecom m en ded m ixt u r e of 50/50
et h ylen e-glycol a n d wa t er will pr ovide pr ot ect ion
a ga in st fr eezin g t o -37° C (-35° F ). Th e a n t ifr eeze
con cen t r a t ion m u s t a lw a y s be a m in im u m of 44 per-
cen t , yea r-r ou n d in a ll clim a t es. If p e rc e n ta g e is
lo w e r th a n 44 p e rc e n t, e n g in e p a rts m a y be
e ro d e d by c a v ita tio n , a n d c o o lin g s y s te m c o m -
p o n e n ts m a y be s e v e re ly d a m a g e d by c o rro s io n .
Ma xim u m pr ot ect ion a ga in st fr eezin g is pr ovided
wit h a 68 per cen t a n t ifr eeze con cen t r a t ion , wh ich
X J
in cr ea sed exh a u st