Jeep Engines - Oljeep

T - T 74.0L POWER TECH IN-LINE 6 (COOLING SYSTEM) 215TroubleshootingThe 4.0L Power Tech engine standard production coolingsystem is adequate at keeping operating temperatures ataccepted levels. However, several components may bechanged to reduce power losses in the system.Not surprisingly, race engine cooling problems arise duringthe summer and tend to disappear in the fall. There arevarious causes: flex-fans, water pumps, radiator size andfunctioning shrouds, grille openings, and fan bladediameter and number. The not so obvious areas areimproper spark advance and too lean fuel mixture.Now, what happens if a racer has fixed all of these problemsand he still overheats or runs too hot? What could thisproblem be? Some people feel this means there is somemysterious design problem with the engine. This is a witchhunt! Generally, engines don’t have an overheatingproblem. Big engines make more heat than small engines,but this just requires a bigger radiator. Put simply, enginesmake heat; cooling systems get rid of heat. Nothing fancy!If your engine overheats, that means the balance betweenthese two functions has been lost somewhere.COOLING SYSTEM HOSES(Refer to Figure 4-40.)Rubber hoses route coolant to and from the radiator, intakemanifold and heater core. The lower radiator hose is springreinforcedto prevent collapse from water pump suction atmoderate and high engine speeds. When performing a hoseinspection, inspect the radiator lower hose for properposition and condition of the internal spring.Warning! Constant tension hose clamps are used on mostcooling system hoses when removing or installing, use onlytools designed for servicing this type of clamp. Always wearsafety glasses when servicing constant tension clamps.Caution: A number or letter is stamped into the tongue ofconstant tension clamps. If replacement is necessary, use onlyan original equipment clamp with matching number or letter.Inspect cooling hoses at regular intervals. Replace hosesthat are cracked, feel brittle when squeezed, or swellexcessively when the system is pressurized.In areas where specific routing clamps are not provided, besure that hoses are positioned with sufficient clearance. Checkclearance from exhaust manifolds and pipe, fan blades, drivebelts and sway bars. Improperly positioned hoses can bedamaged, resulting in coolant loss and engine overheating.SERPENTINE DRIVE BELTCorrect drive belt tension is required to ensure optimumperformance of the belt driven engine accessories. Ifspecified tension is not maintained, belt slippage may causeengine overheating, lack of power steering assist, loss of airconditioning capacity, reduced generator output rate, andgreatly reduced belt life.It is not necessary to adjust belt tension on the 4.0L engines.These engines are equipped with an automatic belttensioner. The tensioner maintains correct belt tension at alltimes. Due to use of this belt tensioner, DO NOT attempt touse a belt tension gauge on 4.0L engines.DiagnosisWhen diagnosing serpentine drive belts, small cracks thatrun across ribbed surface of belt from rib to rib (Figure 4-42) are considered normal. However, cracks running alonga rib (not across) are not normal (Figure 4-42). Any beltwith cracks running along a rib must be replaced. Alsoreplace the belt if it has excessive wear, frayed cords orsevere glazing.Refer to the Serpentine Drive Belt Diagnosis Chart forfurther belt diagnosis.NORMAL-CRACKSBELT OKNOT NORbL CRACKSREPLACE BELTFigure 4 - 42m7-44