Zinc Pencil Anode – Fits Volvo Penta D19 D21 D27 D29 D30 D31 D32 D40 D41 D42 2001 2002 2003 (Replaces 838929, 804107, 800476)

Product Details

This Zinc Pencil Anode is designed for Volvo Penta marine diesel engines, providing essential corrosion protection for critical components including oil coolers, intercoolers, and cylinder heads. Compatible with D-series models (D19, D21, D27, D29, D30, D31, D32, D40, D41, D42) and 2000-series engines (2001, 2002, 2003), this pencil rod anode ensures reliable galvanic protection in saltwater and brackish environments.

This aftermarket replacement directly interchanges with Volvo Penta part numbers 838929, 804107, 800476, 858501, and 3838499, as well as Sierra 18-6001 and GLM 12789.

• Threaded design with multiple mounting options: 7/16 UNC and M8
• 15 mm diameter zinc construction for optimal sacrificial anode performance
• Regular inspection and replacement protects expensive engine components from electrolysis damage

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Technical Specs

Material

Zinc

Diameter

15 mm

Thread Size

7/16 UNC, M8

Application

Oil Cooler, Intercooler, Cylinder Head

OEM Number

838929

What's in the Box

• 1 × Zinc Pencil Anode

Installation Notes

1. Shut down the engine and allow it to cool completely before servicing.
2. Locate the existing pencil anode on the oil cooler, intercooler, or cylinder head.
3. Using the appropriate wrench for 7/16 UNC or M8 thread, carefully unthread the old anode.
4. Inspect the mounting hole for debris or corrosion; clean threads if necessary.
5. Apply a small amount of anti-seize compound to the threads of the new anode to prevent seizure.
6. Thread the new zinc pencil anode into position by hand to avoid cross-threading.
7. Tighten securely with a wrench, taking care not to over-torque and damage threads.
8. Inspect anodes regularly (every 50–100 hours or seasonally) and replace when 50% depleted.

Troubleshooting & FAQ

How often should I replace my zinc pencil anode?

Inspect your anode every 50–100 operating hours or at the beginning of each season. Replace when the zinc material has eroded by approximately 50%. In saltwater or high-electrolysis environments, replacement may be needed more frequently.

What happens if I don't replace a worn anode?

Once a zinc anode is depleted, galvanic corrosion will attack more expensive engine components such as heat exchangers, oil coolers, and cylinder heads. This can lead to leaks, overheating, and costly repairs.

Can I use this anode in freshwater?

Yes, but zinc anodes are most effective in saltwater and brackish conditions. In pure freshwater with low conductivity, zinc anodes corrode more slowly and may provide extended service life.

Which thread size should I use—7/16 UNC or M8?

Check your engine's existing anode or service manual. Both thread options are included to accommodate different Volvo Penta model configurations. Ensure you select the thread that matches your mounting port.

Why is my anode corroding unevenly or not at all?

Uneven corrosion may indicate poor electrical grounding or protective coatings blocking contact. Ensure mounting threads are clean and metal-to-metal contact is solid. If the anode shows no wear, verify your bonding system is correctly connected.

Can I paint or coat the anode?

No. Any coating or paint will insulate the anode and prevent it from functioning. The zinc surface must remain bare to provide galvanic protection.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

• Verify images/specifications against your original part. If anything differs—even if your model appears compatible—do not purchase.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended for safety and performance.

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
• Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
• Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.