Coolant Flush

Complete coolant system flush and refill procedure for 1972 Ford F-100 with 302ci V8, including draining old coolant, flushing the system, and refilling with fresh 50/50 ethylene glycol mixture.

Warnings

Tools required

Parts

• Radiator drain petcock (if damaged) × 1 — Use OEM specification
• Block drain plug washer × 1 — Use OEM specification
• Radiator cap (if damaged or old) × 1 — 13-16 PSI cap

Fluids

• Ethylene glycol green 50/50 — 15 qt

Preparation

1. Ensure engine is completely cold (at least 2 hours after last operation)
2. Park vehicle on level ground and engage parking brake
3. Place drain pan under radiator and position additional pans nearby for block drain
4. Verify you have sufficient coolant on hand (15 quarts total capacity)

Procedure

1. 1

   Remove radiator cap and inspect
   Slowly turn the radiator cap counterclockwise to release any residual pressure, then remove completely. Inspect the cap rubber seals for cracks or deterioration. If the cap is original or shows wear, replacement is recommended.
2. 2

   Drain coolant from radiator
   Locate the drain petcock on the driver side bottom corner of the radiator. Position the drain pan directly underneath. Turn the petcock counterclockwise by hand to open and allow coolant to drain completely. This will take approximately 5-10 minutes for full drainage.
   ℹ️If the petcock is stuck or corroded, apply penetrating oil and wait 10 minutes before attempting to turn.
3. 3

   Drain coolant from engine block
   Locate the engine block drain plug(s) on the side of the block, above the oil pan rail and below the exhaust manifold. Note the 302 has a drain plug on each side of the block; drain both for a complete flush. Reposition the drain pan under this location. Use an appropriately sized socket or wrench to remove the tapered pipe-thread drain plug. Allow the block to drain completely. These plugs seal on their tapered threads; apply fresh thread sealant on reinstallation.
   ℹ️The block drain plug location may have limited access due to exhaust manifold proximity. Work carefully to avoid damaging the threads.
4. 4

   Flush radiator and system
   With both drain points still open, insert a garden hose into the radiator fill neck. Turn on the water at low to moderate pressure and allow fresh water to run through the system until it drains clear from both the radiator petcock and block drain plug. This removes residual old coolant, rust, and sediment. Continue flushing for at least 5 minutes after water runs clear.
5. 5

   Reinstall block drain plug
   Ensure the drain plug threads and block threads are clean. Apply fresh pipe thread sealant to the tapered plug threads. Thread the plug in by hand first to prevent cross-threading, then snug it down with an appropriately sized socket or wrench until sealed.
   Torque spec

   Block Drain Plug25 Nm (18 lb-ft)
6. 6

   Close radiator petcock
   Hand-tighten the radiator drain petcock clockwise until snug. Do not overtighten; a firm hand-tight seal is sufficient to prevent leaks without damaging the brass petcock. Verified detail (The petcock on a 1972 F-100 is brass, not plastic. This warning is inappropriate for the vehicle's original equipment.): Brass petcock threads can be damaged if cross-threaded. If resistance is felt before reaching proper seal, back out and inspect threads for damage or debris. Verified detail (On a 1972 F-100, the original radiator drain petcock is typically a brass/metal petcock, not plastic. Plastic petcocks are a later-model feature. The warning about plastic threads is likely era-inappropriate.): The original brass petcock threads can be damaged if overtightened. If resistance is felt before reaching proper seal, back out and inspect threads for damage or debris. Verified detail (1972 F-100 petcocks are typically brass, not plastic. The material reference is anachronistic for this vehicle year.): Hand-tighten the radiator drain petcock clockwise until snug. Avoid using excessive force to prevent damage to the petcock or radiator threads.
   ⚠Plastic petcock threads strip easily. If resistance is felt before reaching proper seal, back out and inspect threads for damage or debris.
   Torque spec

   Drain Petcock5 Nm (4 lb-ft)
7. 7

   Fill cooling system with fresh coolant
   Using a funnel, slowly pour 50/50 pre-mixed ethylene glycol green coolant into the radiator fill neck. Fill until the radiator is full to the neck. Pause periodically to allow air bubbles to escape. The system holds approximately 14-15 quarts total capacity (verify exact capacity against the factory service manual).
8. 8

   Burp the cooling system
   With the radiator cap still off, start the engine and allow it to idle. As the engine warms and the thermostat opens, coolant level will drop as air is purged from the system. Continue adding coolant to maintain level at the radiator neck. Run until the engine reaches normal operating temperature and the upper radiator hose becomes hot, indicating the thermostat has opened and coolant is circulating fully.
   ⚠Keep hands and tools clear of the fan and drive belts while the engine is running.
9. 9

   Install radiator cap and final check
   With the engine still at operating temperature, top off the coolant to the radiator neck. Install the radiator cap by aligning the tabs and turning clockwise until it locks into position. Rev the engine to 2000 RPM briefly and observe for leaks at the petcock, both block drain plugs, and all hose connections.
10. 10

    Check coolant level after cool-down
    Allow the engine to cool completely (at least 1 hour). Remove the radiator cap and verify coolant level is still at the radiator neck. Top off if necessary. Clean up any coolant spills with shop rags and water.

Reassembly

1. Ensure both the block drain plug and radiator petcock are properly torqued and not leaking
2. Verify radiator cap is fully seated and locked into position
3. Wipe down engine block and radiator to remove any coolant residue

Verification

• With engine cold, verify coolant level is at the top of the radiator neck
• Start engine and bring to operating temperature, checking for leaks at all drain points
• Confirm upper radiator hose becomes hot, indicating proper thermostat operation and coolant circulation
• Check that heater blows hot air when heater controls are set to maximum heat
• Verify no coolant puddles under vehicle after overnight parking

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