Engine Cooling Pump AN3541 | ST-11 Series Raw Water Pump

Engine Cooling Pump AN3541 — ST-11 Series Raw Water Pump

Overview

The AN3541 is an ST-11 series belt-driven raw water cooling pump for marine engine applications. The ST-11 designation identifies the pump body and impeller chamber size within Jabsco’s engine cooling pump series. This pump draws raw water (sea or lake water) from a sea strainer and circulates it through the engine’s heat exchanger or cooling circuit, then overboard. The belt-driven design mounts to the engine and is driven off the engine’s accessory drive system. Confirm the correct port configuration, inlet/outlet sizing, and drive arrangement for your specific engine before ordering.

Compatible Applications

• Marine diesel and gasoline engines using belt-driven raw water cooling pump configurations
• Heat-exchanger cooled inboard engine installations
• Applications requiring an ST-11 series pump body and impeller chamber
• Confirm engine make, model, and existing pump part number before ordering — ST-11 pumps are used across multiple engine brands and configurations

Fitment note: Port configuration (inlet/outlet orientation), shaft direction, and mounting arrangement must be confirmed against the original pump. ST-series pumps are available in multiple port configurations — do not order based on the series designation alone.

Dimensions

• ST-11 series pump body
• Confirm inlet and outlet port sizes against existing pump or engine service documentation before ordering
• Confirm mounting flange pattern and shaft diameter for your engine application

Kit Contents

• 1 × AN3541 ST-11 engine cooling pump assembly
• Impeller included (confirm neoprene or nitrile specification for your application)
• Drive belt not included — replace belt at pump service if worn
• Mounting hardware not included — reuse existing hardware or source separately

Service Interval

Inspect the raw water pump impeller at every annual engine service or every 200–300 hours, whichever comes first. Replace the impeller proactively — a failed impeller can leave rubber fragments in the cooling circuit, causing blockages at the thermostat, heat exchanger, or cylinder head passages. Replace the full pump assembly when:

• The pump body shows cracking, corrosion, or port damage
• The shaft seal leaks internally or externally
• Bearing wear is present (rough rotation or shaft play)
• Impeller wear plate or cam is damaged beyond resurfacing
• After an overheating event that may have run the pump dry

Installation Notes

• Replace the impeller at every pump service — do not refit a used impeller
• Inspect the wear plate and cam for scoring — replace if grooved
• Lubricate the impeller with a small amount of clean water or glycerin before assembly — never use petroleum-based lubricants
• Inspect all hose connections and clamps at the pump inlet and outlet
• Check sea strainer before returning the engine to service
• Verify drive belt condition and tension after installation
• Confirm water flow at the engine overboard discharge after startup
• After any dry-running event, flush the cooling circuit thoroughly and inspect for impeller fragment debris

Related Parts

• Jabsco 7779001 Pulley-Driven Engine Cooling Pump — Neoprene Impeller
• Jabsco 7779003 Pulley-Driven Engine Cooling Pump — Nitrile Impeller
• Ancor Raw Water Pump Impeller AN3830
• Arco WP002 Volvo / Indmar Replacement Water Pump
• Arco WP003 Volvo Replacement Water Pump
• Volvo Penta Impeller Kit 3588475 — OEM Raw Water Pump Service Kit
• Sherwood Impeller Kit 18000K — Raw Water Pump Service Kit

Technical FAQ

How do I confirm this is the correct pump for my engine?

The safest method is to locate the part number on the existing pump body or in your engine’s parts manual, then confirm AN3541 matches that reference. ST-11 series pumps are used on a range of engine brands — the series designation confirms the pump body size but not the port configuration or mounting arrangement. If you are unsure, contact us with your engine make, model, and year before ordering.

What is the difference between neoprene and nitrile impellers?

Neoprene impellers are the standard choice for most raw water cooling applications. Nitrile impellers are recommended where the pump may encounter fuel contamination in the water supply (bilge water ingestion, etc.) or where the manufacturer specifically requires nitrile. Confirm the original impeller material when servicing.

Can I just replace the impeller instead of the full pump?

Yes, in most cases. If the pump body, wear plate, cam, shaft seal, and bearings are in good condition, replacing only the impeller is the standard annual service procedure. Replace the full pump assembly when the body or internal components show damage, wear, or leaks.

What happens if the impeller fails while running?

A failed impeller will reduce or stop raw water flow through the cooling circuit, causing rapid engine overheating. Rubber fragments from a torn impeller can also lodge in the thermostat, heat exchanger, or cooling passages and must be flushed out before returning the engine to service. Proactive annual impeller replacement is the best way to avoid this.

Do I need to replace the drive belt when I replace the pump?

Inspect the belt at every pump service. If the belt shows cracking, glazing, fraying, or has accumulated significant hours, replace it at the same time — it is inexpensive insurance against a secondary failure.

Parts Desk Insights

Best use case: The AN3541 is a replacement ST-11 series belt-driven raw water pump for heat-exchanger cooled marine engines. It is most commonly used in inboard diesel and gasoline applications where the engine drives the raw water pump off the accessory belt system. At this price point, customers are typically replacing a failed or leaking pump assembly after ruling out an impeller-only fix — a worn shaft seal or cracked pump body is the most common reason to replace the full unit rather than just the impeller.

Common customer questions: The biggest issue with ST-series pump orders is port configuration confusion — customers identify the correct pump body series but order the wrong port orientation for their engine’s hose routing. Always ask for the engine make, model, and if possible the existing pump part number or a photo of the pump before confirming the order. The second most common issue is customers skipping the impeller flush-out after an overheating event — remind them that impeller fragments left in the cooling circuit will cause secondary blockages and another overheating failure.