MERCURY 858406T2 Cylinder Head Stbd Optimax Dfi Clean 135 150 175

( Manufacturer Part Number: 858406T2 ), ( Part Type: Hp Cylinder Head ), ( Country Of Manufacture: United States ), ( Donor Motor: 0t146026 10-13-25-2 )

Review MERCURY Cylinder Head Stbd 135 150 175 Hp Optimax Dfi Good Clean Condition fits 2000

The **Mercury 858406T2 2000 cc Outboard Cylinder Head (Right Side, "Stbd")** is a high-performance, precision-engineered component designed exclusively for Mercury s Optimax and DFi (Digital Fuel Injection) outboard motors in the 135, 150, and 175 horsepower range. This cast aluminum cylinder head is a critical part of the engine s combustion system, featuring a robust, heat-resistant design optimized for durability and efficiency. The head is engineered to accommodate the 2000 cc displacement, ensuring proper sealing, airflow, and combustion chamber integrity to maximize power output while maintaining reliability under demanding conditions. Its right-side orientation ("Stbd") aligns with the standard mounting configuration for Mercury s outboard engines, allowing for seamless installation and compatibility with the stock intake, exhaust, and valve train components. Built to withstand the thermal and mechanical stresses of high-performance operation, this cylinder head incorporates reinforced valve seats, precision-machined combustion chambers, and integrated spark plug bosses for optimal ignition performance. Whether used for replacement due to wear, damage, or as part of a performance upgrade, this head is compatible with the latest fuel injection systems, ensuring clean-burning efficiency and reduced emissions while delivering the power and responsiveness expected from Mercury s Optimax and DFi platforms. Ideal for both marine and overland applications, this component is a testament to Mercury s commitment to engineering precision, performance, and longevity in their outboard engine lineup.

### **Pros and Cons of Buying a Mercury 858406T2 (2000 Cylinder Head, Stbd, 135/150/175 HP, Optimax DFI, Clean)**

1. **Proven Reliability** The Mercury 858406T2 is a well-established engine, known for durability in marine applications. The Optimax DFI (Direct Fuel Injection) system improves fuel efficiency and performance compared to older carbureted models.

2. **Versatile Power Range** This engine is available in 135, 150, and 175 HP configurations, making it suitable for a variety of boats, from mid-sized cruisers to performance fishing vessels. The 175 HP version offers strong acceleration and towing capability.

3. **Optimax DFI Advantages** The Direct Fuel Injection system reduces fuel consumption, improves throttle response, and provides better cold-start performance. It also helps prevent fuel starvation under heavy loads, a common issue in older carbureted engines.

4. **Aftermarket Support** Being a Mercury 4-stroke, it benefits from a wide range of aftermarket parts, upgrades (such as exhaust systems, turbochargers, or performance chips), and tuning options. Common modifications include cold-air intake upgrades and exhaust tuning for better airflow.

5. **Lower Fuel Consumption Than 2-Strokes** Unlike older 2-stroke outboards, this 4-stroke engine is more fuel-efficient, producing less oil dilution and fewer emissions. This makes it a cleaner and more economical choice for frequent use.

6. **Compatibility with Modern Boats** The 2000 model year cylinder head is compatible with a range of Mercury outboards, including the 150 HP (80 HP marine) and 175 HP (85 HP marine) variants. It can be paired with newer transmissions and controls, making it a good fit for updated boat setups.

7. **Resale Value** Mercury 4-strokes hold their value better than many 2-strokes, especially if well-maintained. A clean, properly serviced 858406T2 will retain more resale appeal than a neglected or modified engine.

8. **Lower Maintenance Than High-Performance Engines** While it s not a stock engine, it s not as demanding as a turbocharged or supercharged setup. Regular oil changes, spark plug replacements, and basic tune-ups keep it running smoothly without extreme costs.

9. **Good for Fishing and Cruising** The torque characteristics of this engine make it well-suited for fishing boats, where steady power and reliability are crucial. It also performs well in cruising applications where smooth operation is preferred over raw speed.

10. **Easier to Find Parts and Mechanics** Since Mercury 4-strokes are widely used, finding a mechanic familiar with this engine is easier than with niche or older models. Dealerships and independent shops stock replacement parts for this engine.

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1. **Age and Wear** The 2000 model year is now over two decades old, meaning components like gaskets, seals, and bearings may be wearing out. A thorough inspection is critical to avoid hidden issues like oil leaks, rod bearing wear, or cylinder head cracks.

2. **Potential for Modification Overuse** If the engine has been heavily modified (e.g., aggressive turbocharging, forced induction, or aftermarket tuning), it may have reduced reliability or increased wear. Stock or lightly modified versions are safer bets.

3. **DFI System Complexity** While the Optimax DFI system is an improvement, it is more complex than carburetors. If the engine has not been properly maintained, the fuel injectors or fuel pump could fail, leading to starting or performance issues.

4. **Transmission Compatibility Issues** Some older Mercury 4-strokes have been paired with non-OEM transmissions (e.g., aftermarket gearboxes). These can cause shifting problems or premature wear. Ensure the transmission is original or properly upgraded.

5. **Fuel and Oil Requirements** Older engines may not perform well with modern fuel blends (e.g., E10 or E15 ethanol fuels), which can cause carbon buildup or fuel system clogging. Using a marine-grade fuel stabilizer and high-quality oil is essential.

6. **Potential for Water Ingestion** If the boat has been used in rough conditions, the engine may have suffered from water ingestion, leading to corrosion inside the cylinder head or block. A compression test and internal inspection are recommended.

7. **Limited Warranty Coverage** Since this is a used engine, any remaining factory warranty (if applicable) is likely expired. Buyers will bear the full cost of repairs if issues arise post-purchase.

8. **Noise and Vibration** Like many older marine engines, this model may produce more noise and vibration than newer, refined 4-stroke outboards. If the engine has not been properly balanced or tuned, this can be a dealbreaker for some owners.

9. **Environmental Regulations** Some newer boats or marinas may have restrictions on older engines due to emissions concerns. While this 4-stroke is cleaner than a 2-stroke, it may not meet the latest EPA or state regulations for certain areas.

10. **Potential for Hidden Damage** Without a professional inspection, issues like cracked cylinder heads, rod knock, or exhaust manifold leaks may go unnoticed. Buyers should demand a pre-purchase inspection by a Mercury-certified technician.

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### **Conclusion and Recommendation**

The **Mercury 858406T2 (2000, Optimax DFI, clean)** is a solid choice for boat owners seeking a reliable, fuel-efficient 4-stroke engine with a balance of power and durability. Its **Optimax DFI system, wide power range, and aftermarket support** make it attractive for fishing, cruising, and light performance applications. However, its **age, potential for hidden wear, and complexity** require careful consideration before purchase.

1. **Demand a Professional Inspection** Have a **Mercury-certified mechanic** perform a **compression test, leak-down test, and internal inspection** to check for rod knock, cylinder head cracks, or fuel system issues. This is non-negotiable for used engines.

2. **Verify Maintenance Records** Ensure the engine has been **regularly serviced** with the correct oil, fuel, and filters. A clean engine with full service history is far more reliable than one with unknown maintenance.

3. **Check for Modifications** If the engine has been **turbocharged, supercharged, or heavily tuned**, research whether these modifications were done professionally. Aggressive mods can void warranties and reduce longevity.

4. **Test the Engine Under Load** Run the engine at **different RPMs and loads** (e.g., trolling, cruising, and wide-open throttle) to listen for unusual noises (e.g., tapping from bearings, exhaust backpressure, or vacuum leaks).

5. **Inspect the Transmission** Ensure the **gearbox is in good condition** and compatible with the engine. Non-OEM transmissions can cause reliability issues.

6. **Consider a Rebuilt Option** If the engine is **not in perfect condition**, a **rebuilt unit from a reputable dealer** (e.g., Mercury Marine or a licensed rebuild shop) may be a safer investment than a used engine with unknown history.

7. **Budget for Potential Repairs** Even a clean engine may require **spark plugs, fuel injectors, or minor seals** replaced. Factor in **$500 $1,500 ** for unexpected repairs if the engine is older.

8. **Compare to Newer Alternatives** If budget allows, newer **Mercury 4-stroke models (e.g., Verado, FourStroke, or newer Optimax engines)** offer **better fuel efficiency, emissions compliance, and warranty coverage**. Weigh the cost of a used engine against the long-term reliability of a newer one.

- **Buy if:** You find a **well-documented, professionally inspected, and lightly used** 858406T2 with a **clean bill of health**. It s a **cost-effective powerplant** for boats where raw speed isn t the priority, and you re willing to invest in maintenance.

- **Avoid if:** The engine has **unknown history, visible wear, or no service records**. The risk of **hidden mechanical issues** outweighs the savings compared to a newer or rebuilt engine.

- **Best Use Cases:** **Fishing boats, cruisers, or performance applications** where **torque, reliability, and fuel efficiency** matter more than cutting-edge technology.

For the best value, **prioritize a clean, inspected engine with full service history** this will maximize its lifespan and minimize future headaches. If possible, **opt for a newer 4-stroke model** if your budget allows, as they offer **better warranty support and modern refinements**.

Details:

Set of heads ones in great shape other has some spots it as seen.

part #: 858406t2 prices

• $80.50-$156.00

specifications ouboaen:

• for makes: Mercury
• for years: 2000
• mpn: 858406t2
• part type: Hp Cylinder Head
• country of manufacture: United States
• donor motor: 0t146026 10-13-25-2

returns ouboaen:

• policy: No Returns

offer ouboaen:

• options: Ship-to-home
• best offers: True
• sold: 0
• started: April 1, 2026
• availability: In Stock
• quantity: 1

seller ouboaen:

• # reviews: 0
• rating: 0.0%
• city: Cumberland Gap, Tennessee

shipping ouboaen:

• cost: $8.65
• service: USPS Ground Advantage
• carrier: USPS
• class: Standard
• type: Calculated
• transit: 5-10 Days

payments ouboaen:

• credit card: Discover
• other
• wallet: Google-pay

general ouboaen:

• Boat Parts > Outboard Engines Components > Other
• condition: Used

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