Jeep Engines - Oljeep

220 MOPAR PERFORMANCE PARTSOnly when sufficient heat is present will the viscous fandrive engage. This is when the air flowing through theradiator core causes a reaction to the bimetallic coil. It thenincreases fan speed to provide the necessary additionalengine cooling.II GRO~VE J9307-25. COOLANTFigure 4 - 45The presence of aluminum components in the coolingsystem requires strict corrosion protection. Maintaincoolant at specified level with a 50/50 mixture of antifreezeand water. If coolant becomes contaminated or looses color,drain and flush cooling system and fill with correctly mixedsolution.Caution: DO NOT use coolant additives which claim toimprove engine cooling.Once the engine has cooled, the radiator dischargetemperature will drop. The bimetallic coil again reacts andthe fan speed is reduced to the previous disengaged speed.Caution: Engines equipped with serpentine drive beltshave reverse rotating fans and viscous fan drives. They aremarked with the word REVERSE to designate their usage.Installation of the wrong fan or viscous fan drive can resultin engine overheating.Caution: If the viscous fan drive is replaced because ofmechanical damage, the cooling fan blades should also beinspected. Inspect for fatigue cracks, loose blades, or looserivets that could have resulted from excessive vibration.Replace fan blade assembly if any of these conditions arefound. Also inspect water pump bearing and shaft assemblyfor any related damage due to a viscous fan drivemalfunction.IMOUNTING NUTTO WATER PUMPFANSViscous Fan DriveOn 4.0L engines, an electric fan is standard and a thermalviscous fan is added on trailer tow packages only. Thethermal viscous fan drive (Figure 4-46) is a silicone fluidfilledcoupling used to connect the fan blades to the waterpump shaft. The coupling allows the fan to be driven in anormal manner. This is done at low engine speeds whilelimiting the top speed of the fan to a predeterminedmaximum level at higher engine speeds.A thermostatic bimetallic spring coil is located on the frontface of the viscous fan drive unit (Figure 4-46). This springcoil reacts to the temperature of the radiator discharge air. Itengages the viscous fan drive for higher fan speed if the airtemperature from the radiator rises above a certain point.Until additional engine cooling is necessary, the fan willremain at a reduced rpm regardless of engine speed.Figure 4 - 46Mopar Performance Parts Viscous Fan PackageMopar Performance Parts has carried a viscous drive fanpackage for years. Viscous drives allow the engine to run ata higher rpm than the fan: that is, the fan slips at high speed.The purpose of a viscous drive is to save horsepower.We receive many calls concerning fans and cooling. A largenumber of viscous fans have been introduced in theafterrnarket over the last few years. This situation caused usto throw some parts on the dyno. The dyno allows us toknow exactly what’s going on. We selected several viscousunits and several different fans. Some of the new fans lookvery nice - six blade, symmetrical. The one we’ve shown inour parts catalog for years is a five blade, asymmetricaldesign, which we’ve always considered to look “funny.”-31