Sierra 18-3109

Keep Your Mercury Outboard Running Cool with Sierra 18-3109 Water Tube

Picture this: you're out on the water, wind in your hair, engine humming smoothly—until overheating rears its ugly head. The cooling system in your Mercury outboard is the unsung hero that keeps things chill under pressure. That's where the Sierra 18-3109 water tube steps in as a reliable upgrade or replacement for the Mercury 23-29804T. Crafted from high-grade materials, this tube efficiently channels cooling water through the exhaust manifold, preventing steam from your motor instead of power from your prop.

Boat owners know the frustration of a clogged or cracked water tube. It leads to skyrocketing temps, potential seizures, and unplanned dock time. The Sierra 18-3109 tackles this head-on with its precise engineering, matching OEM specs for seamless performance. Whether you're prepping for a fishing trip or a weekend cruise, this part restores factory-level cooling without the hassle.

Seamless Compatibility for Popular Mercury Models

Finding the right fit shouldn't be a guessing game. The Sierra 18-3109 directly replaces Mercury 23-29804T and bolts on to a range of 2-stroke outboards, ensuring water flows where it needs to go. It's designed for engines in the 40HP to 125HP range, commonly found in popular models from the '80s through early 2000s. Always cross-check your engine serial number for the best match, but mechanics rave about its plug-and-play reliability.

• Direct OEM replacement for consistent performance
• Fits inline and V6 configurations
• Resists corrosion from saltwater exposure
• Maintains proper water pressure to powerhead and exhaust

Why Sierra 18-3109 Outshines the Competition

Sierra isn't just another aftermarket label—it's trusted by pros for exceeding expectations. Unlike flimsy generics that warp under heat, this water tube uses durable nylon-reinforced construction to handle the rigors of marine life. It reduces backpressure in the exhaust, boosting efficiency and extending engine longevity. Owners report cooler running temps by 10-15 degrees post-install, translating to fewer repairs and more time on the water.

Think long-term: a proactive swap during routine service avoids catastrophic failures. Saltwater boaters especially appreciate its UV and chemical resistance, outlasting stock parts in harsh environments.

Step-by-Step Installation Guide

No need for a marine yard—most DIYers knock this out in under an hour with basic tools. Here's how:

1. Power down and disconnect the battery for safety.
2. Drain the cooling system and remove the lower unit if needed for access.
3. Unclip the old 23-29804T tube from its manifold mounts—watch for brittle clips.
4. Insert the Sierra 18-3109, ensuring secure seating and hose connections.
5. Refill with fresh antifreeze mix, reconnect, and test-run while monitoring temps.

Pro tip: Flush the system thoroughly first to clear debris. If you're dealing with a stubborn fit, a touch of marine grease on O-rings eases everything into place.

Proactive Maintenance for Peak Performance

To maximize lifespan, inspect your water tube annually or every 50 hours. Look for cracks, soft spots, or buildup—early signs of trouble. Pair it with a full cooling system flush using a vinegar solution to dissolve minerals. Regularly check water pump impeller wear, as it directly impacts tube flow. This simple routine keeps your Mercury purring and your adventures uninterrupted.