How to Install a Radiator Fill Tube Sleeve on 2023.5+ Harley-Davidson Models

The radiator fill tube sleeve from Brock Black Designs is one of the cleanest, easiest upgrades you can make to your 2023.5+ Harley-Davidson. No tools required — just a careful hand and two minutes. Here's how to install it correctly and keep your cooling system in top shape.

Before You Begin

Inspect the sleeve to confirm it arrived undamaged. If anything is wrong, contact Brock Black Designs at 208-705-0028 (US & Canada only) or visit brockblackdesigns.com.

Fitment / Compatibility

These decorative fill tube sleeves fit 2023.5 and later Harley-Davidson liquid-cooled models. Verify fitment for your specific model at brockblackdesigns.com.

Tools Required

None — this is a tool-free installation.

Step-by-Step Installation

Step 1 – Remove the Reservoir from the Clip

Carefully remove the coolant reservoir from its retaining clip. Handle it gently — the reservoir contains coolant and the pressure cap should remain sealed during this step.

Important: Do NOT remove the reservoir pressure cap. The system may be under pressure even when cold.

Step 2 – Slide the Decorative Sleeve onto the Reservoir Tube

Hold the reservoir vertical throughout this step. Slide the decorative sleeve over the reservoir tube, aligning it so that:

• The face of the decorative sleeve faces forward (toward the front of the bike)
• The empty/open space is on the back side so the sleeve can slide cleanly into the clip

Step 3 – Seat the Sleeve into the Clip

Carefully guide the sleeve back into the retaining clip. Take your time here — if the sleeve binds against the clip during reinstallation, stop and realign before forcing it. Binding the clip and sleeve together can crack or damage the decorative sleeve.

Once seated, confirm the sleeve is flush, forward-facing, and the reservoir is fully secured in the clip.

Checking and Adding Coolant

Any time you remove the reservoir, it's a good opportunity to check your coolant level. Here's how:

Check Coolant Level

• Check with the engine cold and the motorcycle on level ground.
• Use a light source from the opposite side of the reservoir to see the level clearly through the translucent tank.
• Coolant should be between the maximum cold level mark and the cold level mark.
• Do not remove the reservoir pressure cap just to check the level.
• If the reservoir is empty when the engine is cold, inspect for leaks before adding coolant. See a Harley-Davidson dealer if needed.

Add Coolant (If Needed)

1. Allow the engine to cool completely.
2. Remove the decorative sleeve and reservoir from the clip.
3. Remove the reservoir pressure cap.
4. Hold the reservoir vertical.
5. Add Genuine Harley-Davidson Extended Life Antifreeze and Coolant until the level reaches or is slightly above the cold level mark.
6. Reinstall the pressure cap.
7. Replace the reservoir in the clip.
8. Reinstall the decorative sleeve following Steps 1–3 above.

Notice: Always use de-ionized water with antifreeze in the cooling system. Hard water causes scale buildup in water passages, reducing cooling efficiency and risking overheating. If Genuine H-D coolant is unavailable, a mixture of de-ionized water and ethylene glycol-based antifreeze may be used temporarily — switch back to Genuine H-D coolant at the first opportunity.

Clean the Radiator Regularly

While you're in the area, check the radiator inlet surface for leaves and debris. Buildup on the radiator surface degrades cooling performance and can lead to overheating. Clean it off with low-pressure compressed air or a soft brush.

Tips for a Perfect Install

• Keep the reservoir vertical the entire time — tilting it can cause coolant to shift and make the sleeve harder to align.
• Face the decorative design forward before sliding into the clip — it's much harder to rotate once seated.
• Never force the sleeve into the clip. If it's binding, pull back, realign, and try again slowly.
• Use this install as a reminder to check your coolant level — takes 30 seconds while the reservoir is already out.

Shop 2023.5+ Radiator Fill Tube Sleeves

Browse our full lineup of decorative radiator fill tube sleeves for 2023.5+ Harley-Davidson models:

• Blank Sleeve
• Fireball Themed Sleeve
• Crown Themed Sleeve
• Spartan Themed Sleeve
• ST Themed Sleeve

Questions about fitment? Call 208-705-0028 or send us a message — we're happy to help.