Complete cooling system flush and refill procedure for the 1970 AMC Rebel Machine 390ci V8, removing old coolant and contaminants to maintain optimal engine temperature regulation.

Warnings

Tools required

Parts

• Radiator drain petcock (if damaged) × 1 — Inspect before ordering
• Radiator cap gasket (if worn) × 1 — Inspect before ordering
• Lower radiator hose (if deteriorated) × 1 — Use OEM specification
• Upper radiator hose (if deteriorated) × 1 — Use OEM specification
• Hose clamps (if corroded) × 4 — Replace as needed

Fluids

• Ethylene glycol antifreeze/coolant (50/50 mix or concentrate) — 16 qt
• Distilled water (for mixing or flushing) — 16 qt

Preparation

1. Ensure engine is completely cold to the touch before beginning work
2. Park vehicle on level surface and engage parking brake
3. Place protective covering under radiator area to catch coolant spills
4. Remove radiator cap slowly to release any residual pressure
5. Inspect all cooling system hoses for cracks, soft spots, or deterioration and replace if necessary

Procedure

1. 1

   Drain existing coolant from radiator
   Position drain pan under radiator drain petcock located at driver's side bottom corner of radiator. Open petcock by turning counterclockwise with pliers or by hand. Allow coolant to drain completely. If petcock is seized or leaking, remove lower radiator hose at radiator connection instead.
2. 2

   Drain engine block coolant
   Locate engine block drain plugs on both sides of the 390ci V8 block, positioned low on the block near the freeze plugs. Using a standard wrench, remove both drain plugs and allow remaining coolant to drain into pan. Inspect drain plug threads and washers for damage.
3. 3

   Remove thermostat for thorough flushing
   Locate thermostat housing on front of engine (inlet side). Remove two bolts securing housing and lift housing away. Remove thermostat and note orientation of air bleed valve (if equipped). Clean gasket surfaces on housing and intake manifold. Set thermostat aside for reinstallation.
4. 4

   Flush radiator with water
   Close radiator drain petcock. Insert garden hose into radiator filler neck and run fresh water through system until water runs clear from thermostat housing opening. This removes sediment and remaining old coolant from radiator core.
5. 5

   Flush engine block
   With block drain plugs still removed, insert garden hose into thermostat housing opening and flush water through engine block until discharge runs clear from both drain holes. This removes scale and debris from water jackets.
6. 6

   Reinstall block drain plugs
   Clean drain plug threads with wire brush. Install new sealing washers if originals are damaged. Thread drain plugs into block by hand first to prevent cross-threading, then tighten securely. Ensure no leaks are present.
7. 7

   Reinstall thermostat and housing
   Install thermostat into manifold recess with air bleed (spring end) facing up toward housing. Position new gasket on manifold surface. Install thermostat housing and secure with two bolts. Tighten bolts evenly in crisscross pattern to avoid warping housing.
8. 8

   Close radiator petcock
   Ensure radiator drain petcock is fully closed and tight. If petcock was damaged during draining, replace with new unit before proceeding. Verify lower radiator hose is properly secured with clamps if it was removed.
9. 9

   Fill cooling system with coolant mixture
   Using funnel, pour 50/50 mixture of antifreeze and distilled water into radiator filler neck slowly to minimize air pockets. Fill until coolant reaches bottom of filler neck. For the 390ci V8, this requires approximately 16 quarts total capacity.
10. 10

    Burp cooling system to remove air pockets
    With radiator cap still off, start engine and allow to idle. Observe coolant level and add mixture as level drops when thermostat opens. Gently squeeze upper radiator hose several times to help release trapped air. Continue until no more bubbles emerge and coolant level stabilizes.
11. 11

    Test system and check for leaks
    Allow engine to reach normal operating temperature (approximately 180-195°F). Monitor temperature gauge to ensure proper thermostat operation. Inspect all hose connections, drain plugs, and petcock for signs of leakage. Check heater operation by turning heater controls to hot.
12. 12

    Top off coolant and install radiator cap
    With engine still warm but not running, add coolant mixture to bring level to bottom of filler neck. Install radiator cap and ensure it seats properly with gasket making full contact. Wipe down any spilled coolant from radiator and engine surfaces.

Reassembly

1. No disassembly beyond coolant system components is required for this procedure
2. Ensure all hose clamps are tightened securely to prevent leaks under pressure
3. Verify radiator cap is properly seated and locked into position

Verification

• Start engine and allow to reach operating temperature while monitoring for leaks at all connection points
• Verify temperature gauge reads in normal range (180-195°F) indicating proper thermostat function
• Check that heater produces hot air when controls are set to maximum heat
• After first drive cycle, recheck coolant level when engine is cold and top off if necessary
• Inspect ground under vehicle after 24 hours for signs of coolant leakage
• Use hydrometer or refractometer to verify coolant concentration provides adequate freeze protection for your climate

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