Cummins NH 855 NH855 Marine Water Pump - Aftermarket

Cummins NH855 Marine Raw Water Pump & Cooling System Components

The Cummins NH855 marine engine is known for its reliability in high-demand marine environments, from commercial fishing vessels to tugboats and offshore supply ships. Proper cooling is essential for maximizing engine longevity and performance. Diesel Pro Power offers a full line of marine raw water pumps and associated cooling system components for the NH855 engine—ensuring your Cummins setup runs efficiently in harsh saltwater environments.

Explore this comprehensive guide to NH855 raw water pump components, including impellers, thermostats, hoses, zincs, strainers, clamps, and accessories.

Raw Water Pump for Cummins NH855 Marine Engines

Marine Raw Water Pump Overview

The raw water pump on the Cummins NH855 draws seawater into the engine to cool the internal coolant through the heat exchanger. This bidirectional pump is designed to rotate either clockwise or counterclockwise, making it compatible with various NH, NT, and VT series marine configurations.

• Bidirectional rotation (fits both left-hand and right-hand engine setups)

• Pulley-driven design

• 1 1/4" hose ports for simple hose integration

• Engineered for long service life in marine environments

This pump is a direct-fit replacement for Cummins NH855 marine engines as well as closely related models such as the NH220, NH250, and VT555. Whether you're repowering or performing preventive maintenance, replacing the marine water pump is essential for optimal thermal regulation.

Marine Water Pump Impeller for NH855

NH855 Impeller Design and Compatibility

The impeller inside the raw water pump is a key wear item and should be checked and replaced regularly. This specific impeller is built for NH855 and NT855 Cummins marine engines, featuring:

• Double flat shaft for secure connection to the pump drive

• Durable rubber construction with marine-grade reinforcement

• Dimensions: approximately 3.74" in height, 2.48" in width, and 0.98" internal diameter

Frequent impeller inspections are crucial to prevent overheating and ensure reliable seawater flow. Diesel Pro Power supplies high-quality replacement impellers built to resist saltwater degradation.

Thermostats for NH855 Marine Cooling System

Standard 180°F Thermostat

This thermostat maintains optimal operating temperature by regulating the engine coolant flow. It is designed for use with standard NH855 marine configurations:

• Opens at 180 degrees Fahrenheit

• Built to withstand constant temperature cycling

• Direct fit for NH855 and NT855 series

185°F Thermostat for Big Cam Engines

For 'Big Cam' versions of the NH855 and NT855 engines, a slightly higher opening temperature thermostat is available:

• Opens at 185 degrees Fahrenheit

• Recommended for updated cooling strategies or specific OEM requirements

Using the correct thermostat ensures fuel efficiency, reduces emissions, and prevents engine stress under marine load.

Sea Water Pump Hoses and Silicone Coolant Hoses

NH855 Raw Water Pump Inlet & Outlet Hose

Special hoses are available to connect the marine water pump to the heat exchanger or other parts of the cooling system. These hoses are resistant to collapse, saltwater exposure, and vibration.

• Reinforced plain hose for inlet and outlet use

• Designed to fit 1 1/4” port dimensions

• Excellent for OEM and custom marine installations

Silicone Coolant Hoses – Multiple Sizes

Diesel Pro Power also supplies premium silicone coolant hoses in a wide range of diameters to fit various coolant lines on the NH855. These are sold by the foot and cut to order:

• Sizes range from 1" to 4" internal diameter

• High heat and pressure tolerance

• Marine-grade flexibility and durability

• Available in popular sizes: 1-3/4", 2", 2-1/2", 3", and more

Silicone hoses are preferred for marine diesel engines due to their long life, ability to handle high operating temperatures, and superior saltwater resistance.

Zinc Anodes for Cummins NH855 Marine Cooling Protection

Heat Exchanger and Aftercooler Zincs

Marine diesel engines operating in saltwater environments are vulnerable to galvanic corrosion. Zinc anodes protect key cooling components such as the heat exchanger and aftercooler.

• Fits NPT 1/2" brass plugs

• Zinc length: 2"

• Prevents corrosion in raw water passages

Zincs for Fuel Cooler or Oil Cooler

These smaller zincs are engineered for use in Cummins marine fuel coolers or oil coolers:

• Fits NPT 3/8" brass plugs

• Zinc length: 1"

• Essential for long-term protection of internal cooler components

Replace these sacrificial zincs regularly to ensure continued protection against marine corrosion.

Marine Intake Water Strainers

Protecting the Raw Water Pump From Debris

Before raw seawater reaches your NH855 pump, it's important to screen out debris like seaweed, shells, or sediment. Intake strainers help prevent premature wear or clogging.

Strainers are available in the following sizes:

• 1” pipe size: 9.5” height, 5.5” width

• 1.5” pipe size: 11.5” height, 7.25” width

• 2” pipe size: 16” height, 7.5” width

• 2.5” pipe size: 16” height, 7.5” width

Made from corrosion-resistant materials, these strainers are ideal for continuous-duty marine engines like the NH855.

Impeller Puller Tool for NH855

Replacing a raw water pump impeller can be difficult without the right tool. Diesel Pro Power offers a specialized impeller puller designed to remove stubborn or swollen impellers from NH855 pumps without damage.

• Reduces risk of damaging the pump housing

• Increases speed and safety of maintenance

• Reusable for multiple impeller services

This is an essential item for any NH855 marine engine toolkit.

Stainless Steel Hose Clamps for Marine Cooling Systems

To secure hoses on the water pump, heat exchanger, and coolant system, Diesel Pro Power carries marine-grade stainless steel clamps with a wide range of adjustment:

• Available for hose diameters ranging from 9/16" to 3"

• Corrosion-resistant finish suitable for saltwater use

• Tight, leak-proof seal for coolant and raw water applications

Each clamp is engineered for long life in humid and high-vibration marine settings.

Importance of a Complete Cooling System Overhaul

When servicing a Cummins NH855 marine engine, it's important to approach the cooling system holistically. A failing impeller may indicate the need to inspect the thermostat, hoses, strainers, and zincs. Overheating, inconsistent temperatures, or clogged heat exchangers can all stem from small components being overlooked.

Routine inspections and preventive part replacement can prevent costly engine damage. Diesel Pro Power provides the parts and technical knowledge to support full NH855 cooling system overhauls.

Why Choose Diesel Pro Power for NH855 Marine Cooling Parts?

• Global Shipping – Fast worldwide delivery

• Trusted by 40,000+ customers – Across commercial, military, and private marine sectors

• In-Stock Guarantee – We carry NH855 parts ready to ship

• Expert Support – Decades of marine diesel experience

• One-Stop Shop – Pumps, hoses, thermostats, strainers, and more—all in one place

When uptime matters, Diesel Pro Power delivers the quality and reliability your NH855 marine engine depends on.