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:

•	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. Flush 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. Refer to Diagnostic System Check in order to locate restrictions in the cooling system.