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For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 1998 🢒 S/T Isuzu - 4WD 🢒 Engine 🢒 Engine Cooling 🢒 Coolant Heater Diagnosis

Coolant Heater Diagnosis Cooling System General

       Caution: To avoid being burned, do not remove the radiator cap or surge tank cap while the engine is hot. The cooling system will release scalding fluid and steam under pressure if radiator cap or surge tank cap is removed while the engine and radiator are still hot.

       Caution: As long as there is pressure in the cooling system, the temperature can be considerably higher than the boiling temperature of the solution in the radiator without causing the solution to boil. Removal of the pressure cap while the engine is hot and pressure is high will cause the solution to boil instantaneously -- possibly with explosive force -- spewing the solution over the engine, fenders and the person removing the cap.

    • The engine appears to be overheating, with or without coolant loss. Refer to Fan Clutch Diagnosis .
    • Loss of coolant. Refer to Loss of Coolant .
    • The engine fails to reach normal operating temperature. Refer to Engine Fails To Reach Normal Operating Temperature .

Exhaust Leaks
  1. Drain only enough coolant so that the level is just above the top of the cylinder head. Refer to Cooling System Draining and Filling .
  2. Disconnect the radiator inlet (upper) hose.
  3. Remove the coolant thermostat. Refer to Engine Coolant Thermostat Replacement

    4. Notice: Allowing the drive belt tensioner to snap into the free position may result in damage to the tensioner.

  4. Remove the accessory drive belt. Refer to Drive Belt Replacement in Engine Mechanical-2.2L or Drive Belt Replacement in Engine Mechanical-4.3L.
  5. Start the engine. Increase the engine speed (RPM) several times, while observing the coolant level. Any noticeable rise in the coolant level or the appearance of bubbles may show that exhaust gas is leaking into the cooling system.

Noise

Cooling system noise can be caused by restrictions to coolant flow. This can cause the coolant to boil at some localized point. Symptoms usually appear after extended idling or driving.

  1. Possible symptoms are:
    2. • The engine may make snapping or cracking noises.
    • The radiator hoses may expand or collapse.
    • The coolant heater hoses may vibrate or thump.
    • The coolant heater core may gurgle or surge.
    • The engine overheat lamp may or may not be illuminated.
  2. Backflush the cooling system, then retest. Refer to Flushing .
  3. Use a mechanic's stethoscope to determine what areas are still affected.
  4. Disassemble suspect components for further inspection and cleaning, as necessary.
  5. Use the following diagnostic table in order to locate restrictions in the cooling system.

Cooling System Diagnosis

Step

Action

Value(s)

Yes

No

1

With the engine running and the radiator filler cap off, verify that the coolant is circulating in the radiator.

Is the coolant circulating?

--

Go to Step 3

Go to Step 2

2

Feel around the front of the radiator core. Cold spots mean a blockage.

Are there cold spots?

--

Go to Step 4

Go to Step 3

3

Remove the coolant outlet. Refer to Thermostat Replacement.

Is the thermostat stuck closed or is the coolant outlet blocked?

--

Go to Step 4

Go to Step 6

4
  1. Inspect the coolant passage.
  2. Probe the blockage with a piece of wire and flush until clear.
  3. Reinstall the component.

Is the system OK now?

--

System OK

Go to Step 5

5

Install new parts as necessary.

Is the system OK now?

--

System OK

Go to Step 1

6

Inspect the crossover passage at the front of the inlet manifold (the thermostat must be removed for access).

Is this area clear?

--

Go to Step 7

Go to Step 4

7
  1. Remove the coolant pump.
  2. Remove the rear cover.

Is there a blockage?

--

Go to Step 4

Go to Step 8

8
  1. Remove the cylinder head(s).
  2. Check for discoloration or other signs of a blockage.

Does the cylinder head(s) require further inspection?

--

Go to Step 4

Go to Step 9

9

Use a penlight to inspect the engine block for a clogged coolant passage.

Has a blockage been found?

--

Go to Step 4

Go to Step 4

Coolant Heater Diagnosis Cooling System Testing

Caution: To avoid being burned, do not remove the radiator cap or surge tank cap while the engine is hot. The cooling system will release scalding fluid and steam under pressure if radiator cap or surge tank cap is removed while the engine and radiator are still hot.

Cooling System Check

The following tests are checking for the normal operation of these cooling system components. If more detailed information or further testing is needed, refer to the cooling system diagnostic charts located in this service category. Refer to Fan Clutch Diagnosis or Loss of Coolant or Engine Fails To Reach Normal Operating Temperature .

Coolant Pump Test
  1. Bring the engine up to normal operating temperature.
  2. Squeeze the (upper) radiator inlet hose, while accelerating the engine speed. You should feel a pressure surge.
  3. Check for a plugged vent hole in the coolant pump.

Radiator Test
  1. Bring the engine up to normal operating temperature.
  2. Turn the engine OFF.
    3. • The radiator should feel hot along the left side.
    • The radiator should feel warm along the right side.
    • There should be an even temperature rise from the right to the left.
  3. Cold spots indicate there are clogged sections of the radiator core.

Thermostat Test
  1. Use a tempilstick in order to find the opening and the closing temperatures of the coolant thermostat.
    2. • J 24731-188 tempilstick melts at 87°C (188°F). The thermostat should begin to open.
    • J 24731-206 tempilstick melts at 97°C (206°F). The thermostat should be fully open.
  2. Replace the coolant thermostat if it does not operate properly between this temperature range.