Volvo Penta Seawater Pump Impeller O-Ring 3858938

Volvo Penta OEM Seawater Pump Impeller O-Ring Part No. 3858938

Compatible Applications

Match this O-ring to the specific seawater pump installed on the engine Volvo Penta used several different raw-water pump designs across similar engine families. Confirm the installed pump part number and engine serial number before ordering.

• Volvo Penta 3.0GS
• Volvo Penta 4.3GL / 4.3Gi / 4.3GXi
• Volvo Penta 5.0GL / 5.0Gi / 5.0GXi
• Volvo Penta 5.7GL / 5.7GS / 5.7Gi / 5.7GXi
• Volvo Penta 8.1Gi
• Volvo Penta V6-200 / V6-225
• Volvo Penta V8-225 / V8-270 / V8-300 / V8-320
• DPX375 / DPX420 applications (verify by pump part number)

When to Replace

Replace this O-ring any time the seawater pump is opened for impeller service. Even if the seal looks intact on the bench, a flattened, hardened, or slightly nicked O-ring will not seal correctly under operating pressure. Replacing it during each impeller service is standard practice and costs far less than reopening the pump for a leak.

Service Interval

Inspect and replace with each impeller service typically every 12 seasons or 100200 hours, per the Volvo Penta maintenance schedule for the engine. Replace immediately if any coolant seepage or pump weeping is observed at the impeller cover.

Installation Notes

Clean the O-ring groove and mating pump surface before installation. Seat the new O-ring evenly and verify it is not pinched or twisted before reassembling the pump cover. A light coat of clean fresh water or O-ring compatible lubricant helps prevent rolling during installation. While the pump is open, inspect the impeller, pump body bore, and shaft seal area for wear.

Technical FAQ

Is this the same as a thermostat housing O-ring?
No. Some reseller listings incorrectly describe 3858938 as a thermostat housing seal. Pump-component catalogs and parts diagrams consistently identify this part as the seawater pump impeller O-ring. If you need a thermostat housing seal, confirm the correct part number against your engines cooling-system diagram.

Can I reuse the old O-ring if it looks okay?
Not recommended. O-rings compress and harden over time and may appear serviceable on the bench but fail under pump pressure. Replacing it each time the pump is opened is the lower-risk choice.

What else should I replace during impeller service?
While the pump is apart, inspect the impeller, pump body, wear plate, and shaft seal. Replacing the impeller, O-ring, and cover gasket as a set is common practice during scheduled maintenance.

Does this fit all Volvo Penta raw-water pumps?
No Volvo Penta used several different seawater pump assemblies across these engine families. Confirm the installed pump part number and your engine serial number before ordering to ensure 3858938 is the correct O-ring for your specific pump.

Parts Desk Insights

This O-ring is most commonly needed during scheduled impeller replacements and is easy to overlook in a kit order. The most common issue is customers ordering by engine model rather than by pump part number since Volvo Penta used multiple pump designs on similar engines, the installed pump is the reliable fitment reference. Its a low-cost add to any impeller service order and avoids a callback for a pump leak.