Sierra Distributor Cap 18-5389, Replaces Mercury Marine 393-4988T, for Ford & GM V-8 Engines

The Sierra 18-5389 Distributor Cap is a metal, machined-finish replacement distributor cap built for Ford and GM V-8 marine engines running Autolite or Mercury ignition systems. It uses a twist-on closure for a secure, positive seal against moisture and vibration, both common failure points for marine ignition components operating in a harsh onboard environment. The white housing protects the internal contacts while distributing spark to each cylinder in firing order, and the cap is engineered to meet or exceed the specifications of the original equipment part it replaces.

This cap is a straightforward tune-up and ignition-maintenance item, suited for scheduled replacement as part of routine engine service or as a direct fix for a cracked, arced, or corroded cap. It ships as a single component and is intended to be matched with a compatible rotor and ignition coil for the engine it is installed on.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-5389
• Color: White
• Material: Metal
• Exterior Finish: Machined
• Closure Type: Twist-On
• Item Dimensions: 0.39 x 0.39 x 0.39 inches
• Weight: 0.67 pounds
• Compatible Engines: Ford and GM V-8 engines with Autolite or Mercury ignitions
• UPC: 030999236678

Fitment

• Ford V-8 marine engines with Autolite ignition
• GM V-8 marine engines with Autolite or Mercury ignition

Replaces (OEM)

• 393-4988T2
• Crusader 3000121
• Mercury Marine 393-4988T

Frequently Asked Questions

What engines does the Sierra 18-5389 distributor cap fit? The 18-5389 fits Ford and GM V-8 marine engines equipped with Autolite or Mercury ignition systems.

Is the 18-5389 cap a direct replacement for a Mercury Marine cap? Yes, this Sierra cap cross-references to Mercury Marine 393-4988T and 393-4988T2, along with Crusader 3000121, so it is a direct equivalent for those OEM part numbers.

What material is the Sierra 18-5389 distributor cap made from? It has a metal body with a machined exterior finish and a white housing.

How does the cap attach to the distributor housing? The 18-5389 uses a twist-on closure type rather than screw-down clips.

How much does the 18-5389 distributor cap weigh? It weighs 0.67 pounds.

What are the dimensions of this distributor cap? The Sierra 18-5389 measures 0.39 x 0.39 x 0.39 inches.

Does the 18-5389 come with a rotor or gasket? No, the 18-5389 is supplied as the distributor cap only; it does not include a rotor or gasket.

Is this a genuine Sierra part or an aftermarket copy? The 18-5389 is a genuine Sierra part, manufactured to meet or exceed the specifications of the original equipment component it replaces.

Will the 18-5389 work on an engine with points-type ignition? The 18-5389 is designed for Ford and GM V-8 engines with Autolite or Mercury ignitions; check your existing ignition type before ordering, as it is not listed for other ignition configurations.

How do I know if my distributor cap needs replacing? Common signs include visible cracking, carbon tracking, corrosion on the internal contacts, or a rough-running engine; the 18-5389 is intended as a direct replacement when the original cap shows this kind of wear.

What is the UPC for the Sierra 18-5389 distributor cap? The UPC for the Sierra 18-5389 distributor cap is 030999236678.