1. Introduction
This instruction manual provides essential information for the proper installation, operation, and maintenance of the Sierra 18-8903 Impeller. The impeller is a vital component of your marine engine's water pump system, responsible for circulating cooling water to prevent overheating. Adhering to these instructions will help ensure the longevity and optimal performance of your engine.
2. Product Overview
The Sierra 18-8903 Impeller is a high-quality replacement part designed to meet or exceed original equipment specifications. It features a durable, flexible material with multiple vanes (typically six) that draw water into the cooling system. This impeller is specifically engineered for compatibility with various marine engines.
Interchangeability: This impeller is interchangeable with the following OEM part numbers:
- Chrysler/Force/US Marine: 47-F436065-2
- GLM: 89614
- Mallory: 9-45004
Figure 2.1: The Sierra 18-8903 Impeller. This image displays the black, six-bladed impeller, which is a crucial part of a marine engine's water pump for cooling.
3. Specifications
| Feature | Specification |
|---|---|
| Brand | Sierra |
| Model Number | 18-8903 |
| Item Weight | 1.6 ounces |
| Material | Flexible Polymer (Impeller), Aluminum (Hub) |
| Operation Mode | Motor |
| Mounting Type | Engine Mount |
| Maximum Horsepower | Up to 25 HP (for compatible engines) |
| OEM Part Number Cross-Reference | Chrysler/Force 47-F436065-2 |
| UPC | 808282106669 |
Note: The material specification for the impeller itself is typically a flexible polymer (rubber-like), while the hub may contain metal components.
4. Safety Information
Always prioritize safety when working on marine engines. Failure to follow safety precautions can result in serious injury or damage to equipment.
- Disconnect Power: Before performing any maintenance or installation, ensure the engine's battery is disconnected to prevent accidental starting.
- Engine Cooling: Allow the engine to cool completely before working on the cooling system to avoid burns from hot water or engine components.
- Personal Protective Equipment: Wear appropriate safety glasses, gloves, and other protective gear.
- Proper Tools: Use the correct tools for the job to prevent damage to parts and ensure secure fastening.
- Disposal: Dispose of old parts and fluids responsibly according to local regulations.
5. Installation (Setup)
Impeller replacement typically involves accessing the water pump housing, usually located in the lower unit of an outboard engine. If you are unfamiliar with this procedure, it is recommended to consult a qualified marine technician.
General Installation Steps:
- Preparation: Ensure the engine is off, cooled, and the battery is disconnected. Place the boat on a stable surface or trailer.
- Drain Gearcase Oil: If necessary, drain the gearcase oil to prevent spillage during lower unit removal.
- Remove Lower Unit: Carefully unbolt and remove the lower unit from the mid-section of the outboard engine. Refer to your engine's service manual for specific instructions.
- Access Water Pump Housing: Locate and disassemble the water pump housing. This usually involves removing bolts and separating the housing halves.
- Remove Old Impeller: Extract the old impeller. Note the orientation of the impeller vanes before removal, as the new impeller must be installed in the same direction. Inspect the housing for wear or damage.
- Clean Components: Thoroughly clean the water pump housing, wear plate, and any other components. Remove any debris, corrosion, or old gasket material.
- Install New Impeller: Lubricate the new Sierra 18-8903 Impeller with a small amount of water or silicone grease. Install it into the pump housing, ensuring the vanes are correctly oriented (they will bend slightly to fit).
- Reassemble Water Pump: Install new gaskets and O-rings as required. Reassemble the water pump housing, ensuring all bolts are tightened to the manufacturer's torque specifications.
- Reinstall Lower Unit: Carefully reinstall the lower unit, ensuring the driveshaft and shift rod engage correctly. Tighten all mounting bolts to specifications.
- Test: Reconnect the battery. With the engine in water or connected to a flush kit, start the engine and check for a strong, steady stream of cooling water from the tell-tale (pee hole). Monitor engine temperature.
6. Operation
Once installed, the impeller operates continuously when the engine is running, drawing water from the surrounding environment through the lower unit and circulating it through the engine's cooling passages. This process dissipates heat generated by the engine, maintaining optimal operating temperatures.
Key Operational Check:
Always verify that a steady stream of water is exiting the tell-tale (indicator stream) shortly after starting the engine. A weak, intermittent, or absent stream indicates a potential issue with the water pump or cooling system, which could lead to engine overheating.
7. Maintenance
Regular maintenance of your impeller is crucial for preventing engine damage due to overheating.
- Inspection: Inspect the impeller annually or at the beginning of each boating season. Look for cracks, tears, hardening, or missing vanes.
- Replacement Interval: It is generally recommended to replace the impeller every 100 hours of operation or every two years, whichever comes first, even if it appears to be in good condition. This is a preventative measure as impellers can degrade over time due to heat, chemicals, and wear.
- Winterization/Storage: If storing the engine for an extended period, ensure the cooling system is properly drained to prevent freezing damage. Some technicians recommend removing the impeller during long-term storage to prevent the vanes from taking a permanent set.
8. Troubleshooting
If you experience issues with your engine's cooling system, the impeller is often a primary suspect.
Common Symptoms of Impeller Failure:
- Engine Overheating: The most common symptom. The engine temperature gauge will rise into the red zone.
- No Water from Tell-Tale: A complete absence of water discharge from the indicator stream.
- Weak or Intermittent Water Stream: The tell-tale stream is not strong and steady, indicating reduced water flow.
- Steam from Engine: Visible steam emanating from the engine block, indicating severe overheating.
If any of these symptoms occur, immediately shut down the engine to prevent further damage. Inspect the water pump and impeller. Obstructions in the water intake or cooling passages can also cause similar symptoms, so check these areas as well.
9. Warranty and Support
Sierra products are manufactured to meet or exceed original equipment quality standards, ensuring reliability and performance. For specific warranty information or technical support regarding your Sierra 18-8903 Impeller, please refer to the official Sierra website or contact their customer service department. Always provide your product model number (18-8903) and any relevant engine details when seeking support.
For additional resources and product information, you may visit the Sierra Store on Amazon.
