Engine Cooling System & Automatic Transmission Cooling System: Overview Jeep Commander I

DESCRIPTION

The cooling system regulates engine operating temperature. It allows the engine to reach normal operating temperature as quickly as possible, maintains normal operating temperature and prevents overheating.

The cooling system also provides a means of heating the passenger compartment. The cooling system is pressurized and uses a centrifugal water pump to circulate coolant throughout the system. A separate and remotely mounted, pressurized coolant tank using a pressure/vent cap is used.

OPERATION

The cooling system regulates engine operating temperature. It allows the engine to reach normal operating temperature as quickly as possible. It also maintains normal operating temperature and prevents overheating.

The cooling system also provides a means of heating the passenger compartment and cooling the automatic transmission fluid (if equipped). The cooling system is pressurized and uses a centrifugal water pump to circulate coolant throughout the system.

Coolant flows through the engine block absorbing the heat from the engine, then flows to the radiator where the cooling fins in the radiator transfers the heat from the coolant to the atmosphere. During cold weather the ethylene-glycol or propylene-glycol coolant prevents water present in the cooling system from freezing within temperatures indicated by mixture ratio of coolant to water.

OPERATION - 5.7L/3.0L DIESEL

The hydraulic radiator cooling fan used on the 5.7L and 3.0L Diesel engines replaces both the electric fan and the engine driven mechanical fan. This provides 5.7L and 3.0L Diesel equipped vehicles with heavy trailer towing capability while at the same time reducing unnecessary power drain on both the engine and the vehicles electrical system.

Connecting the power cord to a grounded 110-120 volt AC electrical outlet with a grounded, three wire extension cord activates the heating element warming the engine coolant.

Scheme 1

If the unit does not operate, possible causes can be either the power cord or the heater element. Test the power cord for continuity with a 110-volt voltmeter or 110-volt test light. Test heater element continuity with an ohmmeter or a 12-volt test light.

The Engine Coolant Temperature (ECT) sensor is used to sense engine coolant temperature. The sensor protrudes into an engine water jacket.

The ECT sensor is a two-wire Negative Thermal Coefficient (NTC) sensor. Meaning, as engine coolant temperature increases, resistance (voltage) in the sensor decreases. As temperature decreases, resistance (voltage) in the sensor increases.

At key-on, the Powertrain Control Module (PCM) sends out a regulated 5 volt signal to the ECT sensor. The PCM then monitors the signal as it passes through the ECT sensor to the sensor ground (sensor return).

When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer air-fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.

The PCM uses inputs from the ECT sensor for the following calculations

1. for engine coolant temperature gauge operation through CAN BUS communications
2. Injector pulse-width
3. Spark-advance curves
4. ASD relay shut-down times
5. Idle Air Control (IAC) motor key-on steps
6. Pulse-width prime-shot during cranking
7. O2 sensor closed loop times
8. Purge solenoid on/off times
9. EGR solenoid on/off times (if equipped)
10. Leak Detection Pump operation (if equipped)
11. Radiator fan relay on/off times (if equipped)
12. Target idle speed

Scheme 2

1. Remove air cleaner assembly. Refer to «REMOVAL»(ref-288233-S39673722052008062000000) .
2. Partially drain the cooling system.
3. Disconnect the electrical connector (2) from the engine coolant sensor (1).
4. Remove the sensor from the intake manifold.

Scheme 3

The Engine Coolant Temperature (ECT) sensor on the 5.7L engine is located under the air conditioning compressor. It is installed into a water jacket at the front of the cylinder block.

Scheme 4

1. Partially drain the cooling system. See «STANDARD PROCEDURE»(ref-288235-S07920148752008062000000) .
2. Remove accessory drive belt. See «REMOVAL»(ref-288235-S32167489122008062000000) .
3. Carefully unbolt air conditioning compressor from front of engine. Do not disconnect any A/C hoses from compressor. Temporarily support compressor to gain access to ECT sensor. Refer to «HEATING & AIR CONDITIONING - SERVICE INFORMATION»(ref-288218) article for information.
4. Disconnect electrical connector from sensor.
5. Remove sensor from cylinder block.

Scheme 5

1. Disconnect negative battery cable.
2. Remove engine cover.
3. Partially drain coolant system. See «STANDARD PROCEDURE»(ref-288235-S07920148752008062000000) .
4. Unplug coolant temperature sensor electrical connector. NOTE: Capture any residual coolant that may flow.
5. Remove coolant temperature sensor.

Scheme 6

The ECT sensor is located near the front of the intake manifold.

1. Partially drain cooling system. See «STANDARD PROCEDURE»(ref-288235-S07920148752008062000000) .
2. Disconnect electrical connector from ECT sensor.
3. Remove sensor from intake manifold.

Scheme 7

1. Apply thread sealant to sensor threads.
2. Install sensor to engine.
3. Tighten sensor to 11 N.m (8 ft. lbs.) torque.
4. Connect electrical connector to sensor.
5. Replace any lost engine coolant. See «STANDARD PROCEDURE»(ref-288235-S07920148752008062000000) .

The wax pellet is located in a sealed container at the spring end of the thermostat. When heated, the pellet expands, overcoming closing spring tension and water pump pressure to force the valve to open.

The thermal viscous fan drive is a silicone-fluid-filled coupling used to connect the fan blades to the water pump shaft. The coupling allows the fan to be driven in a normal manner. This is done at low engine speeds while limiting the top speed of the fan to a predetermined maximum level at higher engine speeds.

An electrical cooling fan located in the fan shroud aids in low speed cooling, It is designed to augment the viscous fan, However, it does not replace the viscous fan.

Scheme 8

A thermostatic bimetallic spring coil is located on the front face of the viscous fan drive unit. This spring coil reacts to the temperature of the radiator discharge air. It engages the viscous fan drive for higher fan speed if the air temperature from the radiator rises above a certain point. Until additional engine cooling is necessary, the fan will remain at a reduced RPM regardless of engine speed. Normally less than three hundred (300) RPM.

Only when sufficient heat is present, will the viscous fan drive engage. This is when the air flowing through the radiator core causes a reaction to the bimetallic coil. It then increases fan speed to provide the necessary additional engine cooling.

Once the engine has cooled, the radiator discharge temperature will drop. The bimetallic coil again reacts and the fan speed is reduced to the previous disengaged speed.

DESCRIPTION-WATER PUMP BYPASS-3.7/4.7L

The 4.7L engine uses an internal water/coolant bypass system. The design uses galleries in the timing chain cover to circulate coolant during engine warm-up preventing the coolant from flowing through the radiator. The thermostat uses a stub shaft located at the rear of the thermostat to control flow through the bypass gallery.

A centrifugal water pump circulates coolant through the water jackets, passages, intake manifold, radiator core, cooling system hoses and heater core, this coolant absorbs the heat generated when the engine is running. The pump is driven by the engine crankshaft via a drive belt.

OPERATION-WATER PUMP BYPASS-3.7L/4.7L

When the thermostat is in the closed position the bypass gallery is not obstructed allowing 100% flow. When the thermostat is in the open position the pill partially covers the bypass hole, reducing the amount of bypass flow. This design allows the coolant to reach operating temperature quickly when cold, while adding extra cooling during normal temperature operation.

A vent valve in the center of the cap will remain shut as long as the cooling system is pressurized. As the coolant cools, it contracts and creates a vacuum in cooling system. This causes the vacuum valve to open and coolant in reserve/overflow tank to be drawn through connecting hose into radiator. If the vacuum valve is stuck shut, or overflow hose is kinked, radiator hoses will collapse on cool-down.

Scheme 9

Remove cap from radiator. Be sure that sealing surfaces are clean. Moisten rubber gasket with water and install the cap on pressure tester (tool 7700 or an equivalent).

Operate the tester pump and observe the gauge pointer at its highest point. The cap release pressure should be 110 to 138 kPa (16 - 20 psi). The cap is satisfactory when the pressure holds steady. It is also good if it holds pressure within the 110 - 138 kPa (16 - 20 psi) range for 30 seconds or more. If the pointer drops quickly, replace the cap.

The automatic transmission/power steering cooler assembly is located in the front of the A/C condenser and behind the front fascia. The transmission cooler is a heat exchanger that allows heat in the transmission fluid to be transferred to the air passing over the cooler fins.

The transmission oil/power steering cooler assembly is equipped with quick connect fitting for the transmission oil and power steering lines.

The transmission oil/power steering cooler is serviced as an assembly.

Scheme 10

1. Remove dust cap by pulling it straight back off of quick connect fitting. (Scheme 10)
2. Place disconnect tool Special Tool 8875A onto transmission cooler line with the fingers of the tool facing the quick connect fitting.
3. Slide disconnect tool down the transmission line and engage the fingers of the tool into the retaining clip. When properly engaged in the clip, the tool will fit flush against the quick connect fitting.
4. Rotate the disconnect tool 60° to expand the retaining clip.
5. While holding the disconnect tool against the quick connect fitting, pull back on the transmission cooler line to remove.

Scheme 11

1. Align transmission cooler line with quick connect fitting while pushing straight into the fitting.
2. Push in on transmission cooler line until a "click" is heard or felt. (Scheme 11)
3. Slide dust cap down the transmission cooler line and snap it over the quick connect fitting until it is fully seated and rotates freely. (Scheme 11) Dust cap will only snap over quick connect fitting when the transmission cooler line is properly installed.

Note. If dust cap will not snap into place, repeat assembly step 2.