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You should be able to figure it out. It's only two hoses. Think inlet and outlet to the heater core under the dash. The inlet always comes from upper part of engine, where the coolant is the warmest and where it heats up first. The fitting will come from upper part of intake manifold or the cylinder head. then the hose goes to the firewall.
The outlet from the heater core carries coolant back to the engine and almost always to the water pump on the front of the engine. Makes sense, coolant goes back into the water pump and is circulated again back into the engine.
I don't know if top or bottom, but the heater core inlet will be the hose coming from either the intake manifold or a fitting on a cylinder head. The outlet from the heater core goes to the front of the engine, it goes into the water pump. I think all GM engines are like this, and almost all engine designs likewise. On a 1992 3.8L, for example, the heater core inlet hose comes from the intake manifold on the passenger side. The heater core outlet goes into a fitting on the water pump (lower front of engine).
The core may be plugged, or it may have an air lock, or the core may be fine and the doors in the heater case may not be opening properly to pass heat.
With the engine at normal operating temperature, feel both the inlet and outlet core hoses at the firewall. If the coolant is circulating both hoses should be hot. If only one is hot, try cracking open the outlet line, with engine running, to get flow started from an air block. (The outlet line will run from the firewall to the front of engine near or at the water pump housing. The inlet for the heater comes off the top of engine from a head fitting and goes to the firewall.) If no flow results, the core may be plugged. To flush the core, take both hoses off at the firewall or off at where they fit on the engine, and put a garden hose into the outlet-flush it backwards-run until clear-let the water run to ground or use a catch can if able to. Some people use compressed air into the core instead of water flushing. Either way, you should see some sediment come out if it had any blockage. Once you get the heater core circulating, any further heater problems need to be addressed at the heater case. Make sure the temperature blend door can open and close-this door opens to let blower fan air pass across the heater core. Good luck.
Look on the thermostat housing for a bleed valve to let out trapped air. What I would do is take off the heater outlet line and run engine till coolant starts to flow out in a steady stream. It should only take a moment. Which is the outlet? The inlet will come off top of engine, either a cylinder head fitting or the intake manifold, and go to heater. The outlet will likely rout to near the water pump and enter engine there.
Water Pump Replacement (4.8L, 5.3L and 6.0L Engines)
1. Drain the cooling system.
2. Loosen the air cleaner outlet duct clamps at these locations:
Mass Airflow/Intake Air Temperature (MAF/IAT) sensor
3. Remove the radiator inlet hose clip from the outlet duct.
4. Remove the air cleaner outlet duct.
5. If necessary, remove the engine sight shield.
6. Remove the radiator vent inlet hose from the radiator hose clips.
7. Reposition the inlet hose clamp at the water pump.
8. Remove the inlet hose from the water pump.
9. Remove the fan blade.
11. Reposition the outlet hose clamp at the water pump.
12. Remove the outlet hose from the water pump.
13. Reposition the surge tank outlet hose clamp at the water pump.
14. Remove the surge tank outlet hose from the water pump.
15. Reposition the heater inlet hose clamp at the water pump.
16. Remove the heater inlet hose from the water pump.
17. Remove the water pump bolts.
18. Remove the water pump and gaskets.
19. Discard the water pump gaskets
Installation Procedure Important: All gaskets surfaces are to be free of oil or other foreign material
1. Install the water pump and NEW gaskets
2. Install the water pump bolts.
3. Install the heater inlet hose to the water pump.
Zoom Sized for Print
Notice: Refer to Fastener Notice in Service and Precautions.
2.1. Tighten the bolts a first pass to 15 Nm (11 ft. lbs.).
2.2. Tighten the bolts a final pass to 30 Nm (22 ft. lbs.).
4. Position the heater inlet hose clamp at the water pump.
5. Install the surge tank outlet hose to the water pump.
6. Position the surge tank outlet hose clamp at the water pump.
7. Install the outlet hose to the water pump.
8. Position the outlet hose clamp at the water pump.
9. Install the accessory drive belt.
10. Install the fan blade.
11. Install the inlet hose to the water pump.
12. Position the inlet hose clamp at the water pump.
13. Install the engine vent inlet hose to the radiator hose clips.
14. If necessary, install the engine sight shield.
Important: Align the arrow at the throttle body end of the duct with the throttle
body attaching stud.
15. Install the air cleaner outlet duct
16. Install the radiator inlet hose clip to the outlet duct.
17. Tighten the air cleaner outlet duct clamps at these locations:
MAF/IAT sensor Tighten the clamps to 7 Nm (62 inch lbs.).
18. Fill the cooling system.
I hope this helps. The numbering is incorrect in the sequence but the instructions are correct.
Most newer units have a brass inlet on the valve and a plastic outlet. Older modles have a plastic garder hose type fitting for inlet and same smaller plastic thread for outlet Some models have push in connectors called John Guess fittings the do not require threading.