cooling

Radiator Cap

for 2021 Honda Civic 1.5L I4 Turbo · FWD

Editorial review:Chris Hackleman — Master Technician · 20+ years · Jeff Moore — Master Lexus & Toyota Mechanic · 20+ years

Difficulty

Easy

Time

6 min

Tools

Steps

✓Expert-verified. Personally reviewed and approved by OLP's master technicians (Chris Hackleman & Jeff Moore — 20+ years each). Always follow the vehicle's factory service information and torque specs.

This procedure covers the replacement of the radiator cap on a 2016-2021 Honda Civic with the 1.5L turbo engine, a simple maintenance task requiring no disassembly.

Warnings

⚠️Never remove the radiator cap when the engine is hot. Hot coolant and steam can spray out under pressure causing severe burns.

⚠Always allow the engine to cool completely (at least 1 hour after shutdown) before attempting to remove the radiator cap.

Tools required

Shop towel or ragEssential

Parts

Radiator cap × 1 — Honda 19045-5AA-A01 or equivalent

Preparation

Ensure the engine has been off for at least 1 hour and is completely cool to the touch
Open the hood and locate the radiator cap on top of the radiator at the front of the engine bay
Visually inspect the area around the radiator cap for any coolant leaks or residue

Procedure

1
Test Engine Temperature
Carefully touch the radiator and upper radiator hose with the back of your hand to confirm they are cool. If there is any heat present, wait longer before proceeding.
2
Remove Old Radiator Cap
Place a shop towel over the radiator cap. Press down firmly on the cap while turning it counterclockwise to the first stop. Wait a few seconds to allow any residual pressure to release, then press down again and continue turning counterclockwise to remove the cap completely.
3
Inspect Cap and Filler Neck
Examine the old radiator cap rubber seals for cracks, deformation, or hardening. Inspect the radiator filler neck threads and sealing surface for damage or corrosion. Clean any debris from the filler neck with a clean shop towel.
4
Install New Radiator Cap
Verify the new radiator cap has intact rubber seals and matches the pressure rating of the original (typically 1.1 bar/16 psi for this vehicle). Place the new cap onto the radiator filler neck, press down firmly, and turn clockwise until it stops and locks into place. You should feel a definite click or resistance when properly seated.

Reassembly

No reassembly required for this procedure

Verification

Start the engine and allow it to reach normal operating temperature while monitoring the temperature gauge
Check for any coolant leaks around the radiator cap
After the engine cools, verify the radiator cap is still properly seated and locked
Monitor coolant level in the overflow reservoir over the next few days to ensure the cap is maintaining proper system pressure

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