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TheMasterTechSource, Senior Automotive Consultant
Category: Car
Satisfied Customers: 211
Experience:  ASE Master-37 YRS- Master Certified Tech and a Fixed Operations Specialist
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2004 Chevy Blazer: V..4x4..a loud knocking noise when cold..coolant

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I have a 2004 Chevy Blazer, 4.3 Liter V-6 with a/c and 4x4. My problem is a loud knocking noise when cold but quickly subsides when truck is warm. I know it is some type of coolant problem so I have just replaced the simple things first. So far, I have replaced the water pump, radiator and hoses, thermostat. The problem is still there. It is very hard to tell where the coolant is leaking from, but sometimes it doesnt leak at all and sometimes it is just a drip or two. It must be losing coolant when it is driving but hard to tell. It is not the heater core. Inside truck is very warm, sometimes overly hot. It appears to be running hot but temp gauge seems correct at about 190 degrees and holding steady while running. Do you think it could be the intake manifold gasket or the head gasket?
The most likely cause of this coolant leak is the intake manifold gasket --the most likely cause of the cold engine knocking noise is upper cylinder carbon
Customer: replied 8 years ago.
Thanks for the quick response but if it is the intake manifold gasket, do you have any tips to make the job any easier? Also, with this upper cylinder carbon, can this create major engine problems if not taken care soon? How do I take care of the upper cylinder carbon problem?

Carbon knock can be addressed by using a upper cylinder carbonizing product you would put in the fuel--ie. BG 44K----or Barttlemans--sold at Walmart in auto section


Just short of replacing the intake gaskets--there are some good cooling system stop leaks out there--see your local GM parts department for the GM stop leak pills

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