Coolant Heater Diagnosis. GMC Truck Jimmy

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 Jimmy - 2WD 🢒 Engine 🢒 Engine Cooling 🢒 Coolant Heater Diagnosis

Coolant Heater Diagnosis Exhaust Leaks and Noise

Exhaust Leaks

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

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

Remove the accessory drive belt. Refer to Drive Belt Replacement in Engine Mechanical-2.2L or Drive Belt Replacement in Engine Mechanical-4.3L.
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.

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. Possible symptoms are:

•	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.

Use the following procedure to remove any restrictions in coolant flow.

Backflush the cooling system, then retest. Refer to Flushing .
Use a mechanic's stethoscope to determine what areas are still affected.
Disassemble suspect components for further inspection and cleaning, as necessary.
Refer to Coolant Heater Diagnosis in order to locate restrictions in the cooling system.

Coolant Heater Diagnosis Cooling System Testing

Step	Action	Value(s)	Yes	No
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.
1	Does the engine appear to be overheating, with or without loss of coolant?	--	Go to Engine Overheating	Go to Step 2
2	Is a loss of coolant evident?	--	Go to Loss of Coolant	Go to Step 3
3	Does the engine fail to reach the normal operating temperature?	--	Go to Engine Fails To Reach Normal Operating Temperature	Go to Step 4
4	With the engine cold, remove the radiator cap. Remove a small amount of coolant from the radiator in order to prevent overflow as the engine warms up. Run the engine until the thermostat opens. Verify that the coolant is circulating in the radiator. Is the coolant circulating?	--	Go to Step 6	Go to Step 5
5	Feel around the front of the radiator core. Cold spots mean a blockage. Are there cold spots?	--	Go to Step 7	Go to Step 6
6	Remove the coolant outlet. Refer to Engine Coolant Thermostat Replacement . Is the thermostat stuck closed or is the coolant outlet blocked?	--	Go to Step 7	Go to Step 9
7	Inspect the coolant passage. Probe the blockage with a piece of wire and flush until clear. Reinstall the component. Is the system OK now?	--	System OK	Go to Step 8
8	Install new parts as necessary. Is the system OK now?	--	System OK	Go to Step 4
9	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 10	Go to Step 7
10	Remove the water pump. Remove the rear cover. Is there a blockage?	--	Go to Step 7	Go to Step 11
11	Remove the cylinder head(s). Inspect for discoloration or other signs of a blockage. Does the cylinder head(s) require further inspection?	--	Go to Step 7	Go to Step 12
12	Use a penlight to inspect the engine block for a clogged coolant passage. Has a blockage been found?	--	Go to Step 7	Go to Step 7

Water Pump Test

Bring the engine up to normal operating temperature.
Squeeze the (upper) radiator inlet hose, while accelerating the engine speed. You should feel a pressure surge.
Inspect for a plugged vent hole in the water pump.

Radiator Test

Bring the engine up to normal operating temperature.
Turn the engine OFF.

•	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.

Cold spots indicate there are clogged sections of the radiator core.