Complete coolant system flush and refill for 1966 Corvette 327ci V8, including radiator drain, engine block drain, system flush, and refill with proper antifreeze mixture.

Warnings

Tools required

Parts

• Radiator drain petcock (if damaged) × 1 — Use OEM specification
• Block drain plug washer × 2 — Use OEM specification

Fluids

• DEX-COOL Extended Life (Orange) — 10 qt
• Distilled water (for flushing) — 15 qt

Preparation

1. Ensure engine is completely cold to the touch (at least 2 hours since last operation).
2. Park vehicle on level ground and engage parking brake.
3. Place drain pan underneath radiator and have additional pans ready for block drains.
4. Locate radiator drain petcock on driver side lower corner of radiator.
5. Locate engine block drain plugs on both sides of the block, below the exhaust manifolds approximately at the freeze plug level.

Procedure

1. 1

   Remove radiator cap and drain radiator
   With engine cold, slowly remove the radiator cap by turning counterclockwise. Position drain pan under the radiator drain petcock located on the driver side lower tank. Open the drain petcock by turning counterclockwise by hand only. Allow coolant to drain completely into the pan.
2. 2

   Drain engine block - driver side
   Reposition drain pan under the driver side block drain plug, located on the engine block below the exhaust manifold near the rear freeze plug. Using appropriate socket, carefully remove the block drain plug and allow coolant to drain. Inspect drain plug washer for damage.
   Torque spec

   Block Drain Plug25 Nm (18 lb-ft)
3. 3

   Drain engine block - passenger side
   Move drain pan to the passenger side block drain plug, located in the same relative position as the driver side. Remove the block drain plug using appropriate socket and allow coolant to drain completely. Inspect drain plug washer for damage.
   Torque spec

   Block Drain Plug25 Nm (18 lb-ft)
4. 4

   Flush radiator and engine
   With all drain points still open, insert water hose into radiator filler neck. Run water through the system at moderate pressure for 3-5 minutes until water runs clear from all drain points. This removes remaining old coolant and sediment buildup.
5. 5

   Reinstall block drain plugs
   Apply thread sealant to both tapered pipe-thread block drain plugs (no washer required on SBC pipe plugs). Thread each plug in by hand to avoid cross-threading, then tighten to specification using torque wrench. Ensure plugs are fully seated to prevent leaks.
   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 the brass petcock as it can damage the seat or strip the threads. Verify petcock is fully closed by visual inspection.
   Torque spec

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

   Fill cooling system with 50/50 mixture
   Prepare a 50/50 mixture of conventional ethylene glycol (green) antifreeze and distilled water (5 quarts coolant + 5 quarts water). Using funnel, slowly pour mixture into radiator filler neck until level reaches the bottom of the filler neck (approximately 1 inch below top). Fill slowly to allow air to escape.
8. 8

   Burp cooling system
   With radiator cap still off, start the engine and allow it to warm to operating temperature (approximately 160-180°F). Monitor coolant level and add additional 50/50 mixture as level drops during warm-up. Coolant level will drop as thermostat opens and air pockets escape. Run until upper radiator hose becomes hot, indicating thermostat has opened and coolant is circulating.
9. 9

   Top off and install radiator cap
   With engine at operating temperature, top off radiator to bottom of filler neck. Allow engine to idle for 2-3 additional minutes, checking for leaks at drain plug and petcock locations. Shut off engine and carefully install radiator cap, ensuring it locks into place.
10. 10

    Check overflow tank level
    Verify the overflow tank (mounted on driver side radiator support) contains an appropriate level of 50/50 conventional coolant mixture, leaving room for expansion. This non-pressurized overflow catches expansion as coolant heats.

Reassembly

1. No disassembly was required for this procedure.

Verification

• Start engine and allow to reach operating temperature. Check for leaks at radiator petcock and both block drain plugs.
• Verify upper radiator hose becomes hot, confirming thermostat operation and proper circulation.
• After engine cools completely, recheck radiator coolant level and top off if necessary.
• Check coolant freeze protection using hydrometer or refractometer - should read -34°F protection with proper 50/50 mixture.
• Monitor coolant level over the next few drive cycles and top off as needed while remaining air pockets evacuate.

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