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Why Does My Tonneau Cover Leak At The Tailgate?

A tonneau cover is an important accessory for any pickup truck owner who wants to protect cargo in the truck bed. However, it can be very frustrating when your tonneau cover starts to leak, especially near the tailgate. Water leakage indicates that your tonneau cover is not properly sealed and secured, which allows moisture to seep in. But don’t worry – with some troubleshooting and repair, you can stop the leaking and continue using your tonneau cover to shield your truck bed.

What Causes Tailgate Leaking in Tonneau Covers?

There are several potential reasons why you might notice leaking near the tailgate area of your tonneau cover:

Gaps Between the Bed Rails and Tonneau Cover

Even with the provided seals, over time small gaps can form between the top of the bed rails and the edges of the tonneau cover. These gaps allow water to gradually seep into the truck bed.

The Tailgate Seal Not Properly Compressed

Most tonneau covers come with a bulb seal that runs along the bottom edge and presses against the tailgate when closed. If this bulb seal is not compressed enough to fully touch the tailgate, gaps will be present that allow water intrusion.

Truck Bed Rail, Cap, or Bulkhead Design

Certain truck models seem prone to leaking issues due to how the bed rails, caps, or bulkheads are designed. There may be inherent gaps or seals that deteriorate over time.

Loose or Damaged Bulkhead Seal

If your tonneau cover attaches at the front bulkhead, a loose or damaged seal here can result in leaking. Lack of maintenance or damage from loading/unloading the truck bed can degrade the bulkhead seal.

Small Holes in the Tonneau Cover

Even a tiny hole or puncture in the vinyl or plastic tonneau cover material that you cannot see can lead to leakage. Water will find the smallest opening to get through.

Poor Sealing Around the Perimeter

If the clamps, snaps, or other fasteners around the edges of the tonneau cover are not tight enough, gaps between the cover and your truck bed rails can occur. Water can leak through these perimeter gaps.

How to Troubleshoot and Fix a Leaking Tonneau Cover

Diagnosing the exact cause of leaking by the tailgate and then repairing it takes some time and effort. But solving the problem will lead to better protection for your truck bed cargo. Here are tips on troubleshooting and fixing tailgate leaks:

Inspect and Tighten Seals

Carefully examine the bulb seal along the bottom of the tonneau cover near the tailgate. Look for gaps, cracking, brittleness, or deformities. Make sure the seal evenly compresses against the tailgate along its entire length when closed. Tighten or replace the seal if needed.

Also inspect the perimeter seal around the edges of the cover. Tighten any loose clamps or snaps. Replace any cracked or damaged perimeter sealing.

Check for Gaps and Cover with Sealing Material

Look for small gaps between the tonneau cover and the top of the bed rails, even if you already have seal strips there. Lightly cover any gaps with waterproof sealing material like silicone or water pipe insulation to block moisture. Avoid over-compressing the material.

Test for Leaks with Water

Spray the tonneau cover with a hose, especially near the tailgate and any other suspect areas. Let it sit for 15 minutes, then check under the cover for any water droplets inside the truck bed. Using a bright flashlight can help identify leak points. Mark any leaks to seal.

Disassemble and Reassemble the Tailgate Seal

If you have a vinyl roll-up tonneau cover, unzip and detach the tailgate seal. Examine it for damage and stretched-out sections. Reattach the seal, making sure it’s the proper shortened length to fully compress against the tailgate along the entire width.

Look for Tiny Holes

Carefully inspect the tonneau cover vinyl or plastic sheeting, especially around the tailgate area. Look for miniscule holes or punctures that could be allowing water intrusion. Cover small holes from the inside using plastic sheeting and silicone.

Check Your Bulkhead Seal

Make sure the seal along the front bulkhead of your truck bed is intact and securely attached. Tighten the bulkhead clamps if any sections are loose. Replace any cracked or deteriorated sections of the seal with automotive weatherstripping.

Consider Aftermarket Seal Products

There are various aftermarket products designed to fill in gaps between the tonneau cover and tailgate that allow moisture. Tailgate seal kits cover the perimeter of the tailgate to provide a better barrier.

Replace the Tonneau Cover

If your tonneau cover is several years old and leaks persist after other troubleshooting, it may be time to replace the entire cover. Consider upgrading to a higher-end tonneau cover with sturdier sealing and construction.

Helpful Tips to Prevent Tailgate Leaking

Here are some useful tips to help avoid issues with your tonneau cover leaking near the tailgate in the first place:

  • When installing a new tonneau cover, carefully follow all the provided directions to properly seal it along the tailgate. Taking your time here is important.
  • Periodically inspect perimeter seals and clamps around the cover edges. Tighten or replace them as needed before leaks start.
  • Open your tailgate before opening the tonneau cover. This avoids putting strain on the seals.
  • Use quality automotive protectants on vinyl cover seals to keep them pliable and conditioned.
  • Handle sealing sections damaged by loading/unloading carefully to avoid enlarging holes. Cover immediately.
  • Park your truck undercover when possible to limit water exposure to the tonneau cover.
  • Consider installing mud flaps behind your truck’s rear wheels. This limits water spray hitting your tailgate and tonneau cover.

FAQs About Fixing Tonneau Cover Leaks

Here are answers to some frequently asked questions about repairing tailgate leaks in tonneau covers:

What is the easiest temporary fix for a tonneau cover leak?

For a quick temporary fix, you can tape over small holes or gaps around the tailgate with waterproof tape. Duct tape works in a pinch but deteriorates quickly. Look for automotive or marine vinyl repair tape for longer-lasting patches until you can do a proper seal repair.

What is the best way to seal a leaking vinyl tonneau cover?

First clean the vinyl cover thoroughly around the leak. Let it dry completely. Apply a vinyl adhesive sealant made for automotive and marine use. Carefully spread it over and just beyond the leaking area. Allow to cure fully before using your cover.

Should I use silicone or rubber sealant to fix a tonneau cover?

Silicone sealant is preferred for plastic or fiberglass tonneau covers. Make sure to use one formulated for automotive use. For vinyl covers, a rubber sealant designed for vinyl repair will bond better and last longer.

What is the easiest DIY way to fix a tonneau cover gap?

For quick gap filling, you can often use self-stick foam weatherstrip tape. It comes in various widths. Just cut pieces to fit into any gaps at the tailgate, bed rails, or perimeter. This can act as a good temporary fix or seal supplement until you can replace the cover.

How do I stop water from getting under the tonneau cover seal?

Start by examining all the perimeter seals and replace any that are cracked or deteriorated. Use silicone spray lubricant to keep fresh seals flexible. You can also install plastic sheeting along the inside top of your bed rails to act as an extra water barrier. Just tape it securely in place on the underside of the rail caps.

Protect Your Truck Bed by Fixing a Leaking Tonneau Cover

It can be annoying and damaging when your tonneau cover allows water to leak into the truck bed near the tailgate. But in most cases, you can troubleshoot the source of the leak and repair it yourself using seals, caulking, or tape. Just take the time to properly examine the various sealing points around the tailgate and bed. With some modifications and maintenance to the seals, you’ll stop that leaking for good and continue to reap the benefits of a dry and shielded truck bed.

Meghan Drummond
Meghan Drummond

Meghan has owned trucks for over 20 years and installed her first tonneau cover back in 2005. She has tested over 50 different tonneau cover models hands-on. Meghan has a journalism degree from the University of Florida and previously worked as an auto writer.

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