Mercedes W166 Radiator Expansion Tank Bleed Line Hose Tube Pipe A1665000491

Mercedes W166 Radiator Expansion Tank Bleed Line Hose Tube Pipe is an original cooling system component, designed specifically for the W166 series models. Thanks to its factory geometry and fitment, it ensures stable discharge of excess air from the system, which promotes smooth engine operation and proper coolant circulation. This used OEM component is a sensible choice for cooling system maintenance when you want to maintain a design consistent with the manufacturer's specifications.

Specifications and technical data

• SKU: A1665000491
• Mark: Mercedes (Genuine OE)
• Condition: Used
• OEM Part Number: A1665000491
• Substitutable numbers: A1665000491, A 166 500 04 91
• Category: Other Engine Parts

Function and role of the bleed line

The radiator expansion tank bleed line in the Mercedes W166 is responsible for the controlled discharge of air and vapors from the cooling system into the tank. A properly selected component:

• stabilizes pressure in the cooling system during engine warm-up and cool-down,
• reduces the risk of air pockets forming in the coolant hoses,
• supports the maintenance of the correct fluid level in the expansion tank,
• ensures predictable system behavior in both city and highway conditions. As a result, the cooling system operates more consistently, and the engine is provided with stable temperature conditions across a wide range of loads.

Why it is worth using an original hose for the Mercedes W166

Using a bleed line sourced from Mercedes allows you to maintain the factory flow characteristics and the routing shape of the hose in the engine bay. This is important both for proper bleeding and for:

• collision-free routing relative to other auxiliary components,
• maintaining the correct bending radius without excessive kinking,
• reducing vibrations and stress at mounting points,
• maintaining an aesthetic, organized installation layout. By choosing an original bleed line for the Mercedes W166, you minimize the risk of leaks and issues with improper system bleeding after replacing coolant or other cooling components.

Used condition – practical service benefits

A used bleed line is a solution often chosen for maintenance repairs when it is crucial to maintain compliance with the factory design while optimizing costs. This type of component allows you to:

• recreate the original hose routing in the engine bay without experimenting with aftermarket replacements,
• maintain the consistency of the cooling system with other OEM components,
• preserve the correct diameters and working cross-sections of the hose,
• carry out repairs in a way that is predictable for both the mechanic and the user. This is particularly important in vehicles where the cooling system operates under increased thermal load, and every component matters for the long-term, consistent operation of the engine.

Integration with the cooling system and diagnostics

The radiator expansion tank bleed line in the Mercedes W166 works with other hoses, connectors, and the expansion tank itself to create a cohesive flow system. When diagnosing overheating issues or unstable fluid levels, it is worth checking:

• the tightness of the connections at the ends of the hose,
• the absence of kinks and bends that restrict flow,
• the condition of the outer surface where it contacts other elements,
• proper seating in brackets and guides. A properly selected and installed hose supports the stable operation of the entire cooling system, which translates into a lower risk of failure and more predictable vehicle behavior in daily use. If you are planning a comprehensive repair or upgrade of the cooling system area in your Mercedes and need other elements from the same group, such as additional hoses, connectors, or the expansion tank, check out the available parts in the Other Mercedes category.

Technical support and vehicle design development

The selection of appropriate cooling system components is important not only in Mercedes – similar principles apply to high-performance cars as well. If you are interested in how manufacturers differentiate mechanical elements and cooling between standard and sports versions, it is worth reading the design analysis in the article Audi RS vs other models – what is hidden under the hood and chassis?, which discusses, among other things, the impact of more powerful engines on cooling and braking system requirements. For owners of older Mercedes vehicles who want to consciously use used OEM parts when refreshing their car, the guide The second life of a youngtimer – how used car parts rejuvenate cars from 1998–2012 may also be useful, describing practical modernization and service scenarios using proven salvaged components.