Engine Cylinder Head Plug
Genuine BMW 11-31-7-502-048 Cylinder Head Screw Plug with Gasket Ring M18x1.5
Genuine Porsche 996 104 215 55 Cylinder Head Camshaft End Plug - 996 104 215 55
What Is an Engine Cylinder Head Plug?
The engine cylinder head is one of the most complex and critical assemblies in any internal combustion engine. Cylinder head plugs — sometimes called expansion plugs or pipe plugs — are small but essential sealing components threaded or press-fit into openings within the cylinder head casting. These openings are created during the manufacturing process to allow access for machining internal oil, coolant, and pressure passages. Once machining is complete, the plugs seal those passages permanently, preventing fluid loss and maintaining the internal pressure balance the engine relies on.
Why Cylinder Head Plugs Matter
The cylinder head houses an intricate network of coolant passages, oil galleries, and combustion chambers. As noted in engine engineering references, cylinder head plugs serve as the last line of defense between those internal passages and the outside world. A plug that has corroded, worked loose, or been damaged during a head resurfacing job can allow engine coolant or oil to seep out — leading to overheating, contamination, or worse.
Failure symptoms are easy to miss early on: a faint coolant smell under the hood, a small wet spot on the side of the head, or a slow but persistent drop in coolant level. Left unaddressed, a leaking cylinder head plug can escalate into serious engine damage. Replacing a worn or missing plug is one of the most affordable preventive maintenance tasks on any engine rebuild or head service job.
Types of Cylinder Head Plugs
These plugs come in several configurations depending on the application:
- Cup (expansion) plugs — Stamped steel cups that are driven into a bore and expand outward to form a seal. Ideal for coolant passage openings.
- Pipe plugs (NPT threaded) — Tapered thread plugs, available in hex or square drive configurations, used in oil gallery and coolant passages that require a more secure threaded seal.
- Concave steel expansion plugs — A variation of the cup design with a concave face for improved sealing force in larger openings.
Matching the correct plug type, thread size (such as 1/8-27 NPT, 3/8-18 NPT, or 1/2-14 NPT), and diameter to your specific engine is critical. Always consult your vehicle's service manual or verify fitment by year, make, and model before purchasing.
Shopping Tips
When sourcing a replacement cylinder head plug, prioritize OE-equivalent fit and material quality. Steel construction is standard for most applications, offering the strength and corrosion resistance needed to survive the thermal cycling an engine endures over its service life. During installation, ensure the mating bore is clean and free of debris, and use the appropriate driver or wrench to seat the plug correctly — improper installation is a leading cause of premature plug failure.
Top Brands for Engine Cylinder Head Plugs
Dorman is the leading name in this category, offering a wide range of engine cylinder head plugs — from NPT pipe plugs to cup-style expansion plugs — all engineered as direct OE replacements. Dorman's cylinder head plugs are designed to match the fit and function of the factory part on specified years, makes, and models, backed by a team of U.S.-based product experts with over a century of automotive experience.