MERCURY G603AN Dfi Lower Unit 135-150 2.0L 2/1

( Manufacturer Part Number: G603AN ), ( Part Type: Unit ), ( Engine Hp : 150 )

Review MERCURY Dfi 2.0l 2/1 Ratio Lower Unit Yr Warranty fits MARINER 1979–2014

The **Mercury G/603AN Mariner 135 150 DFi 2.0L Lower Unit (1979 2014)** is a high-performance, marine propulsion system engineered for reliability, power, and versatility, making it an ideal choice for anglers, boaters, and enthusiasts seeking a balance of efficiency and raw driving force. Designed to complement the legendary Mercury 2.0L DFi (Direct Fuel Injection) outboard engine, this lower unit is a critical component that ensures seamless power transfer from the engine to the water, delivering exceptional acceleration, top-end speed, and fuel economy. Built with precision-crafted components, the G/603AN lower unit features a robust **3-bolt lower unit housing**, a hallmark of Mercury s engineering, which enhances durability and reduces stress on the drive shaft during high-speed operation. The **135 150 horsepower range** accommodates a variety of applications, from mid-sized sportfishing boats to performance cruisers, ensuring adaptability for both recreational and competitive use.

One of the standout features of this lower unit is its **optimized gear ratio**, which maximizes torque delivery at lower RPMs while maintaining high-speed efficiency, a crucial advantage for anglers who rely on quick bursts of power to chase down fish or for boaters navigating through choppy waters. The **DFi 2.0L engine integration** further enhances performance with its advanced fuel injection system, which improves throttle response, reduces emissions, and extends engine life by minimizing carbon buildup. The lower unit itself is constructed from high-grade aluminum alloys, resistant to corrosion and wear, ensuring longevity even in the harshest marine environments. Additionally, the **sealed and lubricated drive shaft** minimizes friction and wear, reducing maintenance requirements while maintaining smooth operation.

For those who demand the best in marine propulsion, the **G/603AN lower unit** is equipped with Mercury s **rear-mounted propeller shaft**, which helps balance the boat s weight distribution, improving handling and stability. The unit is also compatible with a wide range of **propeller options**, from high-performance propellers for speed to deep-V designs for better fuel efficiency and reduced wake. Whether paired with a **3-blade or 4-blade propeller**, this lower unit ensures that power is efficiently converted into forward motion, making it a versatile choice for both open-water cruising and tight, maneuverable dockside operations. Built to meet the demands of modern boating, this lower unit is a testament to Mercury s commitment to innovation, ensuring that your vessel not only performs at its best but also remains a reliable companion for years of adventures on the water.

### **Pros and Cons of Buying a Mercury G603AN Mariner 135 150 DFi 2.0L Lower Unit (1979 2014)**

#### **Pros**

1. **Reliability and Durability** The Mercury G603AN is a well-built outboard engine known for its robustness, especially in saltwater environments. The 2.0L DFi (Direct Fuel Injection) model introduced in the late 1990s onward improved fuel efficiency and performance compared to older carbureted versions.

2. **Strong Performance** With 135 150 horsepower, this engine is capable of handling medium-sized boats (18 24 feet) effectively for cruising, fishing, and light planing. The 4-stroke design means fewer oil changes and less maintenance than 2-strokes.

3. **Fuel Efficiency** The DFi system reduces fuel consumption compared to older carbureted models, making it more economical for long trips.

4. **Lower Unit Strength** The lower unit is designed for durability, with a robust gearcase that can handle moderate loads if properly maintained. The 2.0L DFi models (post-1997) feature improved cooling and lubrication systems.

5. **Aftermarket Support** Being a popular Mercury model, parts, service manuals, and performance upgrades (such as exhaust systems, performance chips, or upgraded propellers) are widely available.

6. **Good for Saltwater Use** Mercury outboards are known for their corrosion resistance, though proper maintenance is still critical in saltwater environments.

7. **Resale Value** Well-maintained examples hold decent resale value, especially if they come with service records.

8. **Ease of Maintenance** Compared to older 2-stroke outboards, 4-stroke models like this are easier to service, with fewer moving parts and less frequent oil changes.

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#### **Cons**

1. **Age and Wear** Engines from 1979 2014, especially those without recent service, may have accumulated wear in critical components like the lower unit gears, pistons, or timing chain. A pre-purchase inspection is essential.

2. **DFi System Reliability** While the DFi system improves efficiency, it can be more complex than carbureted setups. Fuel injectors may clog over time, and the electronic ignition can fail if not properly maintained.

3. **Lower Unit Issues** The lower unit (especially in older models) can develop leaks, gear wear, or shaft misalignment. The 2.0L DFi models improved this, but pre-1997 units may be more prone to problems.

4. **Fuel System Vulnerabilities** Older DFi models can suffer from fuel line cracks, clogged injectors, or failing fuel pumps. Saltwater exposure accelerates corrosion in fuel lines and components.

5. **Electrical Problems** The DFi system relies on sensors and wiring that can degrade over time. Issues like faulty crankshaft position sensors or failing alternators are common in older engines.

6. **Cooling System Concerns** The water pump and impeller can wear out, leading to overheating. The 2.0L DFi models have better cooling, but pre-1997 units may struggle in heavy load conditions.

7. **High Maintenance Costs Over Time** While initially reliable, neglect or lack of proper maintenance can lead to expensive repairs, particularly in the lower unit or cylinder head.

8. **Environmental Regulations** Some newer boating areas have stricter emissions or noise restrictions. Older outboards may not meet current standards in certain locations.

9. **Limited Warranty** Most used Mercury outboards from this era will not have any remaining factory warranty, so the buyer bears all repair costs.

10. **Propeller Compatibility** The wrong propeller can strain the engine. A mismatched prop (too large or too small) can cause excessive wear on the lower unit or over-revving.

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### **Conclusion**

The **Mercury G603AN 135 150 DFi 2.0L** is a solid choice for boat owners seeking a reliable, mid-sized outboard with decent performance and fuel efficiency. The DFi models (especially post-1997) are an improvement over older carbureted versions, offering better reliability and efficiency. However, **age-related wear, potential electrical or fuel system issues, and the need for thorough maintenance** are significant considerations.

If you find a **well-documented, recently serviced example** (with records for lower unit flushes, fuel system checks, and electrical diagnostics), this engine can be a **great long-term investment**. If the engine is **neglected or lacks service history**, it may require **significant repairs or replacement of critical components** (lower unit, pistons, or fuel injectors), making it a riskier purchase.

---

### **Recommendation**

- Lower unit gearcase for wear and leaks.

- Cylinder compression test.

- Fuel system (injectors, lines, pump).

- Electrical system (sensors, wiring, alternator).

- Cooling system (water pump, impeller, thermostat).

2. **Prioritize DFi Models (1997 2014)** If possible, choose a **DFi-equipped engine** over carbureted versions, as they are more efficient and reliable.

3. **Check for Service Records** A boat with **regular maintenance logs** (oil changes, lower unit flushes, fuel system cleanings) will be far more reliable.

4. **Budget for Potential Repairs** Be prepared for **lower unit replacement ( $800 $1,500)**, **fuel system upgrades ( $300 $600)**, or **cylinder head work ( $500 $1,000)** if the engine is neglected.

5. **Consider a Used Lower Unit** If the existing lower unit is worn, purchasing a **new or rebuilt Mercury lower unit** (OEM or aftermarket) can extend the engine s life.

6. **Test the Engine Thoroughly** Run the engine at **different loads (idle, cruise, trolling, planing)** to check for unusual noises, overheating, or power loss.

7. **Negotiate Based on Condition** If the inspection reveals issues, use them to **reduce the purchase price** or require the seller to cover repairs.

- **Worth It If:** You find a **well-maintained DFi model (1997 ) with service records**, are prepared for potential repairs, and plan to use it responsibly.

- **Not Worth It If:** The engine is **neglected, lacks documentation, or has obvious wear** (leaking lower unit, rough idle, excessive smoke).

For the best value, **aim for a 2000 2010 model** with a **clean bill of health** from an inspection. If you re on a tight budget, consider a **lower-cost alternative** (such as a Yamaha or Suzuki of similar age) unless you re confident in the G603AN s condition.

Details:

Long #G603AN. 1979-2001 Lower Unit. Two YEAR Extendable WARRANTY. Extra Long #G604AN.

Mercury 135-150 Hp. One Year Extendable Warranty.

part #: g603an prices

• $119.97-$426.71

specifications ouboaen:

• for models: Mariner
• for makes: Mercury
• for years: 1979-2014
• mpn: G603an
• part type: Unit
• engine hp : 150

returns ouboaen:

• policy: No Returns

seller ouboaen:

• rating: 100.0%
• city: Blairsville, Georgia
• # reviews: 1201

offer ouboaen:

• started: May 10, 2026
• quantity: 2
• sold: 0
• options: Ship-to-home
• availability: In Stock

general ouboaen:

• condition: New
• Boat Parts > Outboard Engines Components > Complete Outboard Lower Units

payments ouboaen:

• credit card: Visa
• wallet: Apple-pay
• check
• other

shipping ouboaen:

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