Mercury – Exhaust Manifold Drain T-Fitting | Cooling System Component | Marine-Grade Construction | 863786A1

Overview

Every boater knows the quiet comfort that comes from an engine that drains and dries exactly the way it should at the end of the day. When water leaves the system cleanly and predictably, you are not just protecting metal—you are protecting your peace of mind. That is what this Mercury exhaust manifold drain T-fitting brings back to your V6 or V8. It is one of those small but essential pieces that keeps your cooling system breathing easily, helping you avoid the headaches that come from trapped water, uneven draining, or corrosion that creeps in when you are not looking. When this fitting is working the way it should, everything about your engine’s maintenance routine feels smoother, simpler, and more predictable.

Key Features

• Primary component that directs water flow during manifold draining
• Built from rugged, marine-safe materials designed for longevity
• Precision-molded for a consistent, secure connection within the drain system
• Designed specifically for the water drain layout on select V6 and V8 engines
• Easy to install using standard tools
• Engineered to meet Mercury Marine’s original equipment standards

Engine & Boat Compatibility

• For MerCruiser V6 and V8 engines: 305, 350, and 377 cubic inch displacement
• Fits sterndrive and inboard systems equipped with factory water drain systems
• Ideal for cruisers, sport boats, bowriders, fishing boats, and multi-purpose family boats
• Designed for boats stored in fluctuating climates where proper draining matters most

Performance & Practical Benefits

What seems like a simple fitting makes a surprisingly big difference in real-world use. When the drain system flows freely, you will notice how much smoother your end-of-day routine becomes—no guesswork, no lingering drips, no uneven draining between sides of the engine. Everything feels balanced and predictable. The fitting locks firmly into place with a tight, confident connection, giving you a sense of security every time you winterize, flush the system, or perform routine maintenance.

Durability is another major factor. This fitting stands up to constant vibration, heat cycles, and moisture without warping or loosening. You will not find it softening, cracking, or becoming brittle over the seasons the way some aftermarket fittings tend to do. It simply holds its shape and continues doing its job, keeping the cooling system flowing the way Mercury intended.

In day-to-day boating, that means fewer surprises, fewer corrosion-related repairs, and a smoother-running engine that handles temperature changes more gracefully. It is one of those parts you do not fully appreciate until you replace a failing one—then everything suddenly feels right again.

Why Buy OEM

When it comes to water-contact components, genuine Mercury Marine parts make a difference you can feel.

• Perfect fitment designed for the exact drain layout of your engine
• Materials rated specifically for marine conditions—heat, vibration, and moisture
• Longer service life than many aftermarket alternatives
• Designed to install cleanly without modifying hoses or fittings
• Reliability that helps protect your engine from costly internal corrosion

For a part this important to winterization and daily maintenance, OEM is simply the safer, more practical choice.

FAQ

Q1: Which engines does the Exhaust Manifold Drain T-Fitting 863786A1 fit?

It fits MerCruiser V6 and V8 engines with 305, 350, and 377 cubic inch displacement water drain systems.

Q2: What sets this part apart from aftermarket fittings?

Its durability, exact sizing, and marine-specific construction provide a tighter, more reliable seal.

Q3: How can I confirm it fits my engine?

Check your owner’s manual, service manual, or verify that your engine uses the factory water drain system on these V6 or V8 models.

Q4: Can this fitting be used in both saltwater and freshwater?

Absolutely—it is built to withstand both environments without degrading.

Q5: Is installation straightforward?

Yes. Most boat owners can install it easily using common tools.