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93 GMC Z71 Truck Heater Core

We have a family member that has bought a 93 GMC Z71 Truck with a 350 motor and he has had to replace the Heater Core 4 times. First he drove it 8 months and the core died, then he replaced it drove it 6 months and it died, then he replaced it drove it about a month and it died. When driving it the core dies and he has to stop before the car over heats. What could be causing the Heater Core to die? Someone suggested it was due to the water and a bad electrical charge but honesly we have no clue. Any ideas would be greatly appreciated because we have none!

Perhaps the core is rubbing against the firewall where the inlet and outlet tubes pass through, and it’s just wearing through from vibration.

If the vehicle’s cooling system is filled with a 50/50 mix of water and antifreeze, corrosion should not be a problem.

Could a charge occur strong enough to melt the aluminum weld on the tubes that take the water inside and out of the core? Thanks so much already for your adivce!

The failed heater cores need to be inspected to find out exactly how they failed. Did the same shop replace it each time? They can fail by rubbing as mc suggested. They can fail because the replacement aftermarket units are not designed correctly allowing the coolant to scour holes due to excessive turbulence and velocity. They can also fail due to electrolysis. Electrolysis is caused by a fault in the vehicle’s electrical system. Google electrolysis and heater core for more info and means to test and remedy.

No, you could not melt the heater core or its welds without doing some other obvious damage to the vehicle (like a complete carflagration).

If it’s an aluminum heater core, you have to make sure that any vibration isolators are installed on the new heater core and that the heater core is installed with no binding. The vibration isolators protect the heater core from vibrations so holes aren’t abrated in the heater core. If the aluminum heater core is binding in it’s mount, the aluminum heater core can’t expand and contract with the heating up and cooling down which can result in cracking of the heater core.


Find the engine ground wire that goes from some metal on the engine to (most likely) the firewall. If you can’t find it, make one. That could help if you have a strange charge problem. I found it odd that a wire was needed between engine and body, but if there isn’t one, there could be funny electrical problems. Your radiator cap may hold too much pressure. Not likely but maybe.

Thanks for all the info, I think we have a better idea now whats getting these heater cores!

If you have a multimeter you may check for voltage going through the core. Set it at the lowest voltage (dc), with the engine cold open the radiator cap, start the engine and touch the negative leg to the negative post on the battery or a good ground and the positive inside the coolant (only touch the coolant). If reads more than a few milivolts, it is time to check the ground connectors (loose, corroded or missing). Remember to turn off the engine before coolant start to pour out the radiator.

YOu should have all available electrical systems turned on while doing this, lights, HVAC blower, radiator fan (high),…