Thermostat Housing

Remove and replace the thermostat housing on a 1966 Chevrolet Corvette 327ci V8, including coolant drain, housing removal, gasket replacement, and coolant refill.

Warnings

Tools required

Parts

• Thermostat housing gasket × 1 — Use OEM specification
• Thermostat (180°F or 195°F) × 1 — Use OEM specification

Fluids

• DEX-COOL Extended Life (Orange) — 10 qt

Preparation

1. Ensure engine is completely cold to the touch
2. Place vehicle on level ground and engage parking brake
3. Position drain pan beneath radiator petcock
4. Remove radiator cap slowly to release any residual pressure

Procedure

1. 1

   Drain cooling system
   Open the radiator petcock at the bottom of the radiator and drain coolant into the pan. If the system is heavily contaminated, also remove the lower radiator hose for complete drainage. Allow coolant to drain completely.
2. 2

   Disconnect upper radiator hose
   Loosen the hose clamp securing the upper radiator hose to the thermostat housing neck using a 1/2" socket or screwdriver depending on clamp type. Twist the hose to break the seal and pull it off the housing neck. Inspect the hose for cracks or deterioration.
3. 3

   Remove thermostat housing bolts
   Remove the 2 bolts securing the thermostat housing to the intake manifold using a 9/16" socket. The housing is located at the front of the intake manifold where the upper radiator hose connects. Keep bolts for reinstallation.
4. 4

   Remove thermostat housing
   Carefully lift the thermostat housing away from the intake manifold. The thermostat will likely remain seated in the manifold recess. If the housing is stuck due to old gasket material, gently tap it with a rubber mallet or use a gasket scraper to carefully separate it. Do not pry against the manifold sealing surface.
5. 5

   Remove old thermostat
   Lift the thermostat out of the intake manifold recess. Note the orientation of the thermostat with the spring side facing down into the engine. Inspect the thermostat for corrosion, stuck valve, or mineral deposits.
6. 6

   Clean gasket surfaces
   Use a gasket scraper or razor blade to remove all old gasket material from both the intake manifold sealing surface and the thermostat housing mating surface. Follow with a wire brush if needed. Ensure surfaces are completely clean and smooth with no gouges or scratches. Wipe clean with shop towels.
7. 7

   Install new thermostat
   Place the new thermostat into the recess in the intake manifold with the spring side facing down into the engine block. The thermostat should sit flat in the recess. Ensure the thermostat is the correct temperature rating for your application (typically 180°F or 195°F for a 327).
8. 8

   Install new gasket
   Position the new thermostat housing gasket over the thermostat and align it with the bolt holes in the intake manifold. Some gaskets have a paper backing or adhesive to hold them in place during installation.
9. 9

   Install thermostat housing
   Place the thermostat housing over the gasket and align the bolt holes. Install the 2 housing bolts and tighten in a criss-cross pattern to 15-20 ft-lbs (verify against factory specification). Do not overtighten as this can crack the housing or distort the sealing surface. Verified detail (25-30 ft-lbs is too high for the small cast thermostat housing bolts (typically 3/8" bolts into a cast-iron manifold), risking cracking the housing. SBC thermostat housing bolts are typically torqued around 15-20 ft-lbs. This value should be verified against factory specs.): Place the thermostat housing over the gasket and align the bolt holes. Install the 2 housing bolts and tighten in a criss-cross pattern to approximately 15-20 ft-lbs (verify against factory spec). Do not overtighten as this can crack the housing or distort the sealing surface.
10. 10

    Reconnect upper radiator hose
    Slide the upper radiator hose onto the thermostat housing neck. Position the hose clamp over the neck bead and tighten securely with a 1/2" socket or screwdriver. Ensure the hose is fully seated on the neck.
11. 11

    Close drain and refill cooling system
    Close the radiator petcock. Slowly fill the cooling system through the radiator filler neck with conventional green ethylene glycol coolant mixed to a 50/50 ratio with distilled water (approximately 10 quarts total capacity). Fill until coolant reaches the bottom of the filler neck. Verified detail (DEX-COOL was introduced in 1995 and is an anachronism for a 1966 Corvette. This vehicle originally used conventional green ethylene glycol (IAT) coolant. DEX-COOL (OAT) can also be incompatible with older cooling system materials/solder.): Slowly fill the cooling system through the radiator filler neck with conventional green ethylene glycol (IAT) coolant mixed to a 50/50 ratio with distilled water (approximately 10 quarts total capacity). Fill until coolant reaches the bottom of the filler neck.
12. 12

    Burp cooling system
    With the radiator cap still off, start the engine and allow it to warm up to operating temperature while monitoring coolant level. Add coolant as needed as the thermostat opens and air purges from the system. Run engine until the upper radiator hose becomes hot, indicating the thermostat has opened and coolant is circulating.
13. 13

    Final fill and pressure test
    With the engine at operating temperature, top off coolant to the bottom of the filler neck. Install the radiator cap. Allow engine to continue running for 5 minutes and inspect the thermostat housing for any coolant leaks. Check coolant level again after engine has cooled.

Reassembly

1. Torque thermostat housing bolts in a criss-cross pattern to prevent gasket distortion
2. Ensure hose clamps are positioned over the raised bead on the thermostat housing neck
3. Double-check that the radiator petcock is closed before refilling the system

Verification

• Start engine and verify no coolant leaks at thermostat housing after reaching operating temperature
• Confirm upper radiator hose becomes hot within 5-10 minutes of running, indicating thermostat is opening properly
• Verify coolant level is correct after engine cools completely
• Check that engine temperature gauge reads in normal range during test drive

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