How to Replace the 1990 GMC Truck Heater Core
The heater core on your 1990 GMC truck is a device similar to a radiator that is used to heat up the air before blowing it out into the cabin of your truck. Contained in the dashboard of your truck, the heater core can begin to fail, which may cause the device's coolant to leak out into the passenger compartment. Replacing a heater core is a complex affair that requires the partial disassembly of the truck's dashboard. You can expect to take anywhere from two to three hours replacing your vehicle's heater core.
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Things You'll Need
- Socket wrench
- Open container
- Distilled water
- Philips screwdriver
- Flathead screwdriver
- Coolant
Instructions
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1
Turn the GMC truck off and prop open the hood. Using a socket wrench, manually remove the ground cable from the battery.
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2
Remove the coolant reservoir tank from the engine compartment by pulling it straight out.
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3
Place an open container underneath the radiator and engine drain petcocks. Open the petcocks with a socket wrench and allow all of the liquid to drain into the container.
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4
Close the petcocks and remove the radiator cap. Pour the distilled into the radiator and turn the engine on. Allow the engine to run for five minutes, then turn it off again. Wait another five minutes for the radiator to cool and open the petcocks again, allowing all of the liquid to drain out. Close the petcocks.
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5
Disconnect the heater hoses from the radiator by pulling them off. Remove the four heater case screws at the back of the engine compartment on the passenger's side.
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6
Remove the antenna cable at the mast.
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7
Pull the glove compartment off the dashboard by removing its bolt with a socket wrench.
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8
Remove the two bolts securing the right side kick panel and remove the right side lower dash panel bolt and nut. Use a flathead screwdriver to pry off the lower dash panel.
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9
Remove the two heater case mounting bolts and lift the heater core out of the case. Place the new heater core into the vehicle and reassemble the dashboard.
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10
Reattach the glove compartment and the antenna cable. Reinstall the heater case screws and pour new coolant into the radiator. Reconnect the battery.
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Tips & Warnings
Liquids from the radiator or heater core can reach very high temperatures. Allow them to cool down before performing any other task.
Only use distilled water when flushing the coolant out of the radiator as tap water contains trace amounts of metal and can damage your engine.
