popping noise at operating temp

[jpirie89gmc]

1989 GMC Sierra. This noise started recently after I had my water pump replaced. After that I had thermostat replaced but noise was still there. Only hear it at operating temp, and mostly when braking....goes away couple seconds after stopped. I can feel a vibration that matches the noise right where the heater core is under the dash. Opened heater core cover and no leaks, looks new. Cooling system seems to be working fine (not overheating, plenty of coolant, all hoses are getting hot, etc.). I can't figure this one out. HELP!

[dakccab]

1989 GMC Sierra. This noise started recently after I had my water pump replaced.  After that I had thermostat replaced but noise was still there.  Only hear it at operating temp, and mostly when braking....goes away couple seconds after stopped.  I can feel a vibration that matches the noise right where the heater core is under the dash.  Opened heater core cover and no leaks, looks new.  Cooling system seems to be working fine (not overheating, plenty of coolant, all hoses are getting hot, etc.).  I can't figure this one out. HELP!

 

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Sounds like air trapped in your heater core to me. Your heater core is probably higher than the top of your radiator and still has air in it from draining your coolant to replace the water pump and again the thermostat. Keep checking your coolant level and top off as air works its way to the radiator. Turn your heater control to the high temperature setting so the heater control valve will open and let coolant flow through the heater core. It will take several cycles of running and heating up your engine to operating temperature and cooling to purge all the air. Or possibly your heater control valve is not opening at all to permit coolant to flow through it.

[jpirie89gmc]

1989 GMC Sierra. This noise started recently after I had my water pump replaced.  After that I had thermostat replaced but noise was still there.  Only hear it at operating temp, and mostly when braking....goes away couple seconds after stopped.  I can feel a vibration that matches the noise right where the heater core is under the dash.  Opened heater core cover and no leaks, looks new.  Cooling system seems to be working fine (not overheating, plenty of coolant, all hoses are getting hot, etc.).  I can't figure this one out. HELP!

 

<{POST_SNAPBACK}>

 

 

Sounds like air trapped in your heater core to me. Your heater core is probably higher than the top of your radiator and still has air in it from draining your coolant to replace the water pump and again the thermostat. Keep checking your coolant level and top off as air works its way to the radiator. Turn your heater control to the high temperature setting so the heater control valve will open and let coolant flow through the heater core. It will take several cycles of running and heating up your engine to operating temperature and cooling to purge all the air. Or possibly your heater control valve is not opening at all to permit coolant to flow through it.

 

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Thanks for the reply. I'll try it and see what happens.