engine

Exhaust Manifold Gasket

for 2021 Honda Civic 1.5L I4 Turbo · FWD

Difficulty

Moderate

Time

2.5 h

Tools

Steps

✓Fact-checked. Built from OLP's spec database, then independently fact-checked line by line with every correction applied. Master-tech sign-off by Chris Hackleman is queued. Cross-check torque values against the factory manual, and stop if anything looks unsafe. How our data is made.

Replace the exhaust manifold gasket on a 2016-2021 Honda Civic 1.5L Turbo engine to resolve exhaust leaks between the manifold and cylinder head.

Warnings

⚠️Allow engine to cool completely before beginning work. Exhaust components can cause severe burns for hours after engine shutdown.

⚠Exhaust manifold studs are extremely prone to breaking on turbo engines. Apply penetrating oil 24 hours before work if possible.

⚠O2 sensor threads are fragile. Use proper O2 sensor socket and remove only when engine is warm (not hot) to prevent thread damage.

ℹ️This procedure requires working from above the engine bay. Vehicle lift access is not required but may ease underbody heat shield removal.

Tools required

10mm socket and ratchetEssential

12mm socket and ratchetEssential

14mm socket and ratchetEssential

Torque wrench (10-50 Nm range)Essential

Extension set (3-inch and 6-inch)Essential

Universal jointEssential

O2 sensor socket (22mm or 7/8-inch)Essential

Plastic trim removal tools

Gasket scraper (plastic or brass)Essential

Wire brushEssential

Brake cleaner sprayEssential

Anti-seize compoundEssential

Penetrating oil

Drain panEssential

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Parts

Exhaust manifold gasket × 1 — Use OEM Honda gasket
Exhaust manifold nuts (if corroded) × 8 — M8 flange nuts
Heat shield gasket/seal (if equipped) × 1 — Use OEM specification
Turbo-to-manifold gasket × 1 — Use OEM Honda gasket
O2 sensor (if damaged during removal) × 1 — Use OEM specification

As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.

Fluids

Honda Type 2 Coolant (Blue) — 1 qt

Preparation

Ensure engine is completely cool to the touch (wait minimum 3 hours after last operation)
Disconnect negative battery terminal and secure away from battery post
Remove engine cover by pulling upward on perimeter clips
Spray all exhaust manifold nuts and O2 sensor threads with penetrating oil, allow to soak 15-30 minutes
Place drain pan under vehicle near downpipe connection point

Procedure

1
Remove upper O2 sensor
Disconnect the upstream O2 sensor electrical connector by pressing the tab and pulling away from sensor. Using a 22mm O2 sensor socket, carefully remove the upstream oxygen sensor from the exhaust manifold. Rotate counter-clockwise with steady pressure. If excessive resistance is felt, stop and reapply penetrating oil.
2
Remove heat shield
Locate the exhaust manifold heat shield covering the turbocharger and manifold assembly. Remove all heat shield bolts (typically 4-6 bolts) using a 10mm socket. Some bolts may be accessed from underneath. Carefully lift heat shield away from manifold, noting any clips or retention points.
Torque spec
Heat Shield Bolts10 Nm (7 lb-ft)
3
Disconnect EGR tube (if equipped)
If your vehicle is equipped with an EGR tube connecting to the exhaust manifold, use a 14mm wrench to loosen the tube fitting at the manifold connection point. Support the tube to prevent bending. Disconnect and position aside without placing stress on the EGR valve end.
4
Separate downpipe from turbo
From underneath the vehicle, locate the connection between the turbocharger outlet and the downpipe/catalytic converter assembly. Remove the two flange bolts (12mm or 14mm) connecting these components. Use penetrating oil if bolts resist. Support the downpipe with a strap or stand to prevent stress on hangers.
5
Disconnect coolant lines from turbo (if necessary)
If coolant lines obstruct access to manifold nuts, partially drain coolant from radiator into drain pan until level drops below turbocharger. Disconnect coolant feed and return lines from turbocharger using appropriate wrenches. Plug lines with rubber caps to prevent coolant loss and contamination.
⚠Coolant may still be warm. Wear protective gloves and eye protection when loosening coolant fittings.
6
Remove exhaust manifold mounting nuts
Locate all 8 exhaust manifold nuts securing the manifold to the cylinder head (two per cylinder). Using a 12mm socket with extensions and universal joint as needed, remove nuts in a cold-to-hot pattern (start from outer cylinders, work toward center). Apply steady pressure and stop if any stud begins to turn with the nut—this indicates stud breakage risk.
⚠If a stud begins rotating with the nut, stop immediately. Apply heat and additional penetrating oil, or plan for stud extraction/replacement.
Torque spec
Exhaust Manifold Nuts30 Nm (22 lb-ft)
7
Remove turbo support bracket
Locate the turbocharger support bracket connecting the turbo assembly to the engine block (typically one or two bolts at the bottom of turbo). Remove mounting bolts using 12mm or 14mm socket. This bracket must be removed to allow manifold/turbo assembly to be lifted away from cylinder head.
8
Remove manifold and turbo assembly
With all fasteners removed, carefully work the exhaust manifold and turbocharger assembly away from the cylinder head studs. The assembly is heavy (approximately 20-25 lbs) and awkward to maneuver. Lift upward and toward the front of the vehicle, tilting as needed to clear brake master cylinder and other components. Place assembly on clean workbench.
ℹ️Assembly removal requires careful manipulation through tight engine bay. Having a second person assist with lifting can prevent damage to surrounding components.
9
Remove old gasket and clean mating surfaces
Using a plastic or brass gasket scraper, carefully remove all old gasket material from the cylinder head mating surface. Do NOT use steel scrapers that could gouge the aluminum head. Clean surface thoroughly with brake cleaner and lint-free cloth. Inspect cylinder head surface for warping or damage. Similarly clean the exhaust manifold mating surface on your workbench.
⚠Aluminum cylinder head is soft and easily damaged. Use only non-metallic scrapers on the head surface. Any gouges or scratches can cause future gasket leaks.
10
Inspect and prepare studs
Inspect all exhaust manifold studs in the cylinder head for damage, corrosion, or thread stripping. If any studs are damaged or were extracted during removal, replace using new studs torqued to specification. Clean threads on good studs with wire brush and apply small amount of anti-seize to upper threads (area where nuts will thread on).
Torque spec
Exhaust Manifold Studs15 Nm (11 lb-ft)
11
Install new gasket and position manifold
Place new exhaust manifold gasket onto the cylinder head studs, ensuring proper orientation (gasket should have printing/markings facing outward). Verify all ports align correctly. Carefully lift manifold/turbo assembly and guide onto studs, seating manifold against new gasket. Ensure gasket does not shift during manifold installation.
ℹ️Gasket orientation is critical. Verify the gasket fire ring embossments face toward the manifold, and any UP or FRONT markings are correctly oriented.
12
Install and torque manifold nuts
Thread all 8 manifold nuts onto studs by hand to ensure proper thread engagement. Apply small amount of anti-seize to nut threads. Torque nuts to specification in a hot-to-cold pattern (start from center cylinders, work outward) in three stages: first to 10 Nm (7 lb-ft), second to 20 Nm (15 lb-ft), and final to full specification of 30 Nm (22 lb-ft).
Torque spec
Exhaust Manifold Nuts30 Nm (22 lb-ft)
13
Reinstall turbo support bracket and downpipe
Reinstall the turbocharger support bracket to the engine block and torque mounting bolts to specification. Install new turbo-to-downpipe gasket at the flange connection. Align downpipe to turbo outlet flange and install flange bolts with anti-seize on threads. Torque flange bolts to specification in a cross pattern.
14
Reconnect coolant lines and EGR
If coolant lines were disconnected, reconnect feed and return lines to turbocharger with new sealing washers. Tighten fittings to manufacturer specification (typically hand-tight plus 1/4 turn). If EGR tube was removed, install with new gasket if applicable and torque fitting to specification. Refill coolant system to proper level with Honda Type 2 coolant.
15
Install O2 sensor and heat shield
Apply thin layer of anti-seize compound to O2 sensor threads ONLY (avoid getting anti-seize on sensor tip). Thread O2 sensor into exhaust manifold by hand, then torque to specification using O2 sensor socket. Reconnect O2 sensor electrical connector. Position heat shield over manifold/turbo and install all heat shield bolts, torquing to specification.
Torque spec
Heat Shield Bolts10 Nm (7 lb-ft)

Reassembly

Reinstall engine cover by aligning clips and pressing firmly until all clips engage
Reconnect negative battery terminal and torque to 5 Nm (4 lb-ft)
Double-check all electrical connectors are properly seated, particularly O2 sensor
Verify no tools or materials were left in engine bay

Verification

Start engine and allow to idle. Listen carefully for any exhaust leak sounds from manifold area—should be completely silent
Monitor for any coolant leaks at turbo connections if lines were disturbed
Allow engine to reach operating temperature and verify no leaks appear as components expand
Check for check engine light or fault codes related to O2 sensor or exhaust system
Perform a test drive and verify normal engine performance with no exhaust smell in cabin
After 50-100 miles of driving, re-check manifold nut torque as gasket may settle slightly