* Symptom Diagnosis

Establish what "driving" conditions caused this complaint. Abnormal loads on the cooling system, such as the following may be the problem:

1. Prolonged Idle, Very High Ambient Temperature, Slight Tail Wind at Idle, Slow Traffic, Traffic Jams, High Speed, Steep Grades:
Driving techniques that avoid overheating are:
a. Idle with A/C off when temperature gauge is at end of normal range.
b. Do not increase engine speed for more air flow and coolant flow because the electric motor fan systems are not responsive to engine RPM. The added cooling from higher coolant flow rate is more than offset by increased heat rejection (engine heat added to coolant).

2. Trailer Towing: Consult owner's manual-Trailer Towing. Do not exceed limits.
3. Air Conditioning: Add-on or After Market:
- If add-on or after market A/C is involved maximum cooling components should be installed for the model involved per manufacturer's specifications.
- Further diagnostic checks should not be required.
4. Recent Service or Accident Repair:
- Determine if any recent service has been performed on the vehicle that may affect the cooling system such as engine adjustment (wrong timing), loose or slipping water pump belt, brakes possibly dragging, changed ports -- possibly wrong, recored radiator or cooling system refilling (possibly under-filled or trapped air).
- If investigation reveals none of the above as cause for overheating complaint refer to the following symptoms chart.

SYMPTOM FOLLOWED BY ACTION
Blinking Engine Warning Light Or High Gauge Indication-Without Coolant Loss
Normal with temporary operation with heavy load, towing a light trailer, high outdoor temperatures, and/or on a steep grade.

Coolant Loss
Improper refilling procedures can result in trapped air in the system. As the cooling system operates the pressure cap and coolant recovery 5 stem will deaerate the cooling system. A low coolant level will result in the Coo ant Reserve Tank. Add coolant. If condition persists see System Diagnosis.

Fan Never Runs
Refer to Powertrain Management/Computers and Control Systems procedures for test procedure.

Fan Always Runs
Normal with A/C compressor clutch engaged. Otherwise consult Electrical

Hot Car (Not Engine): Heat Damage, Hot Carpet, Seat, Trunk, Hot Catalytic Converter, Smoke, Burnt Odor
Check heat shielding, exhaust system, emission controls, ignition timing and fuel/air ratio misfiring.

Hot Engine: Crackling Sounds, Hot Smell, Severe Local Hot Spots
A moderate amount of sound of heating metal can be expected with any vehicle. However, a crackling sound from the thermostat housing, a hot smell and/or severe local hot spots on an engine can indicate blocked coolant passages. Inspect for plugged water passages, bad casting, core sand and plugging, a cracked block or head, or a blown headgasket. Usually accompanied with coolant loss.

Coolant Color
Coolant color is not necessarily an indication of adequate temperature or corrosion protection.

Coolant Recovery Bottle: Level Changes
Level changes are to be expected as coolant volume changes with engine temperature. if the level in the bottle is between the Maximum and Minimum marks at normal engine operating temperature, the level should return to within that range after operation at elevated temperatures.

Coolant Recovery Bottle: Coolant NOT Returning
Coolant will not return to the radiator if the radiator cap vent valve does not function, if an air leak destroys vacuum, or if the overflow passage is blocked or restricted. Inspect all portions of the overflow passage, pressure cap, filler neck nipple, hose, and passageways within the bottle for vacuum leak only. Coolant return failure will be evident by a low level in the radiator. Bottle level should increase during heat-up.

CONDITION, CHECKS & DIAGNOSIS

Fig 1 Normal Gauge Travel:

Magnetic 90° Gauge Reads Low

1. Verify gauge -- is temperature really low?
- See Electrical and check temperature sending unit.
- Repair/Replace gauge.

2. Is code 17 set in diagnostics?
- Yes -- Thermostat, No -- Other

3. Does it read cold?
- Wiring disconnect wrong sending unit used, sending unit for HOT lite, not gauge.

4. Coolant level low in cold ambient. (Also poor heater performance)
- Check radiator and CRS for level -- inspect for leaks.

5. Coolant level O.K.
- Check heater controls, doors -- see Heating and Air Conditioning.

Fig 2 Gauge Reading -- Hot Weather -- Heavy Load:

Gauge Reads High -- Without Pressure Cap Blow off without Coolant or Steam from CRS Tank and to Ground
1. Is it really reading high?
- See chart above.

2. If at "H" without other signs of boiling.
- Look for Grounded gauge, sending unit or wire.

3. Coolant level low in Radiator and CRS.
a. Fill full remembering to vent air.
b. Inspect for leaks, repair.
c. Assure Pressure Cap was shut tight and seals at top and bottom of neck are functioning properly.

4. Coolant level low in Radiator but not in CRS.
a. Fill full remembering to vent air.
b. Inspect for leaks and repair.
c. Inspect for leaks in CRS to radiator connection.
d. Assure cap seals at top and bottom.

5. Check freeze point.
a. Adjust to 50/50 Glycol and water.
b. If no reading or below -59°C (- 50°F), mixture is too rich -- clean system before refilling.

6. Assure Coolant Flow.
a. Look for flow through filler neck with some coolant removed and thermostat open.
b. Repair water pump if necessary.

7. Other possible causes.
a. High speed only
- Radiator or Condenser air side plugged
- Radiator core tubes plugged
- Add on A/C without proper radiator
- Engine out of tune (specifications)
- Brakes dragging
- Bug screen
- Trailer towing or hill climbing

b. High and Low Speed
- Thermostat failed partially shut particularly if ambient temperature is below 21°C (70~F) and vehicle has high mileage.
- Condenser or radiator air side plugged.
- Add on A/C.

c. Low Speed -- NOT high speed
- Fan not operating.
- Check Diagnostics.
- Check Fan Motor by wiring to battery, when disconnected from harness -- Check Electrical.

Temperature Gauge Reads Hot with Pressure Cap Blow-off and Steam and coolant to CR5 and to Ground
1. Coolant Level Low in Radiator and CRS
a. Fill Cooling System Full and Vent Air.
b. Inspect for Leaks -- repair.
c. Assure Pressure cap was shut and seals.
d. If low in radiator but not in CRS, also check connection to filler neck and pressure cap sealing.

2. Check Coolant Freeze point.
- Adjust to 50/50 Glycol and water. -37°C (-35°F)

3. Assure Coolant Flow.
a. Look for flow through radiator filler neck with coolant lowered and thermostat open.
b. When accompanied with "metal cracking sound" -- consider core sand and/or bad head casting.

4. Thermostat failed shut.
- Especially in cold to medium ambient temperatures.

5. Head Gasket Leak
- Use block leak checker.

Temperature Gauge Is Inconsistent -- Cycles-Erratic

Fig 3 Normal Reaction To Fan Cycle:

1. Is cycle normal?
a. Normal Fan Cycle Due to Temperature. Raises Slowly-Drops Fast.

Fig 4 Gauge Reaction To Thermostat:

b. Normal Thermostat Cycle

Fig 5 Gauge Reaction -- Winter, Idle, Heater On:

c. Normal cycle at idle in winter with Heater on high. (Heater Heat Transfer exceeds engine -- Heat Rejection -- drops lower with time. Sometimes noticed in winter between Drive and Idle

Fig 6 Gauge Reaction -- Stop After Heavy Use:

d. Hot water normal build up at stop after heavy use

2. Is coolant level low in radiator (Low level can trap air in system which can put thermostat pellet in air and it opens late).
- Fill system, vent air and inspect for leaks.

3. Is there a head gasket leak that puts exhaust gas in system? (This acts like trapped air with same effect as 2 above.)
a. Test with block leak checker and replace if necessary.
b. Coolant in engine oil.
c. White steam coming out of exhaust.

4. Water pump impeller loose on shaft, slips sometimes.
- Replace.

5. Air lead on suction side of water pump entraining air; see 2 above.
- Find leak and repair.

Warning Light Glows All the Time (No Gauge)
1. Check temperature sending unit The sending unit For a light is a switch an has a screwdriver slot in the electrode that is used for calibration. The gauge sending units do NOT have a screwdriver slot.
- It is probably a sending unit For a gauge, NOT For a light.

Pressure Cap Blow-Off, With Steam to CR5 and Coolant to Ground Without High Reading. Temperature Gauge Above Normal.
1. Check pressure cap relief pressure.
- Replace if lower than 14 psi.

Coolant Loss to Ground Without Pressure Cap Blow-Off
1. Leaks.
a. Pressure test system while shaking hoses.
b. Water pump seal. See "water pump."

Coolant Loss Past Pressure Cap Top Seal-Glycol Seen on Filler Neck
1. With normal gauge reading.
a. Cap not on tight.
b. Top seal leaking.
c. Cap diaphragm "oil canned."
d. Filler neck damaged.
e. Rubber seal out of position.

2. With high gauge reading or low gauge reading on new vehicle.
a. CRS hose kinked.
b. CRS tank and plastic tube plugged.
c. Pressure cap rubber seal out of position.

Detonation or Pre-Ignition When Nothing to Cause It in Engine or Ignition
1. Check freeze point of coolant. If tester does not register reading or the reading is below -59°C (-50°F), be aware that 100% glycol makes engine metal run hotter even without a hot gauge reading.
a. Adjust coolant to 50/50 glycol and water -37°C (-35"F).
b. If 100% glycol has been found in the system, clean and flush the system before replacing with 50/50 glycol and water.

Hoses Observed Collapsing on Cool-Down
1. Check pressure cap vent valve.
a. Must be free to move. Gasket swell can prevent valve from opening.
b. Replace cap.

2. Check CRS hose for kinking or plugging.
- Repair as required.

3. Inside of cap plugged with stop leak pellet, green silica gel, or fiberglass.
- Clean cap.

Fan Runs All the Time
1. Check for relay.
- See Electrical.

Fan Noisy
1. Check for loose fan.
- Repair as necessary.
2. Check for fan clearance to adjacent parts.
3. Check for loose mount fasteners.
4. heck far bent fan blades.
5. Check for fan blades spinning on hub.
6. Check for air obstructions an radiator or condenser

CONDITION, CHECKS & DIAGNOSIS

Inadequate Air Conditioning Performance -- Cooling System Suspected
1. Check for plugged air side of condenser and radiator front and rear.
- Wash out with low-velocity water.

2. Assure fan runs whenever A/C head pressure exceeds 1724 kPa (250 psi).
- Repair as necessary.

3. Check for missing air seals-recirculating air path.

4. Assure correct cooling system parts.

Battery Dead -- Suspect Fan Current Draw as Cause
1. With a good, fully charged battery.
a. Assure fan control is operating properly.
b. See Charging System.

Hot Smell -- Suspect Cooling System
1. Was temperature gauge high?
- Yes, See "Gauge Reads High"
- No, See 2, 3, 4, and 5.

2. Heat shields all in place?
- Yes, See 3, 4, and 5.
- No, Repair or replace heat shields.

3. Fan control operating properly?
- Yes, See 4 and 5.
- No, See Radiator Fan Control

4. Heat exchanger air side plugged?
- Clean as required.

5. Engine missing or running rich?
- Repair as required.

Poor Driveability -- Suspect Failed Open Thermostat
1. Check diagnostics - is code 17 set? (Engine to cold to long)
- If yes, change thermostat.

Poor Heater Performance -- Suspect Failed Open Thermostat
1. Does gauge read low?
- See 3

2. Check coolant level.
- See 3

3. Check diagnostics - is code 17 set? (Engine too cold too long)
- If yes, change thermostat.
- If no, check heater bypass valve, which should be closed except in Max A/C or off mode; if not, see Heating and Air Conditioning.

Steaming, Observe Water Vapor Through Grill or Head Gap at Standstill at Idle -- In Wet Weather
1. This is normal. It is moisture, snow, or water on the outside of the radiator that evaporates when the thermostat opens to put hot coolant into the radiator. This usually occurs in cold weather with no fan or air flow to blow it away.
- Normal condition - no service required.