Product Overview

The coolant expansion tank cap, OEM number 17117639021, is fitted across an exceptionally wide range of BMW models, including the E60/E61 5 Series, E63/E64 6 Series, E9x M3, F01/F02 7 Series, F07 5 Series GT, F10 5 Series, E70/F15 X5, E71/F16 X6, X5 M, X6 M, M4 GTS, M5, M8, and Alpina B7, spanning production from 2004 through 2025. Since this cap spans nearly all of BMW's inline-6 and V8-powered vehicles across two decades of production, it's an exceptionally high-turnover part number worth stocking in significant volume for distributors serving BMW cooling system parts demand.

A worn or failing expansion tank cap typically shows up as coolant loss without a visible leak, a coolant warning light, or engine overheating from loss of cooling system pressure. GSK Auto manufactures this cap to OEM specification at our Ningbo, China facility, with every unit tested before packing. We supply at wholesale volume with low MOQ and support private label packaging, with our team available to confirm fitment before shipping.

Replacement OEM Numbers

Cross-Reference OEM Number

17-11-7-639-021, 17137516004, Febi Bilstein 17117639021, Rein (OE-equivalent)

(Confirm against your VIN or chassis code before ordering — these are commonly listed cross-references for this application, not a guarantee of exact fitment for every variant. Replaces earlier part number 17-13-7-516-004. Driver-side position, 2.0 bar rating for large expansion tank applications.)

What Is a Coolant Expansion Tank Cap?

Function: The expansion tank cap seals the coolant reservoir and maintains cooling system pressure, which raises the coolant's boiling point and helps prevent overheating and coolant loss.

Working Principle: A spring-loaded pressure relief valve inside the cap maintains a set pressure within the cooling system, venting excess pressure if it exceeds the design limit while sealing the system under normal operating conditions.

Importance: On a wide range of BMW inline-6 and V8-powered platforms, a properly sealed and pressure-rated expansion tank cap is essential for maintaining cooling system pressure and preventing overheating.

Common Failures & Signs: Coolant loss over time without a visible external leak. Coolant warning light or low coolant message on the dashboard. Engine overheating from reduced cooling system pressure. Weak or perished seal allowing pressure to escape prematurely.

Key Features

OEM-standard fitment - matches factory pressure rating and thread specification for the 17117639021 application.

Durable construction - built to withstand sustained heat cycling and system pressure.

Excellent fitment - direct drop-in replacement, no modification required.

Tested before shipment - every unit checked for proper pressure rating before packing.

Reliable performance - restores factory cooling system pressure and prevents coolant loss.

Benefits

Importers - covers expansion tank cap demand across nearly all of BMW's inline-6 and V8-powered lineup from one part number.

Wholesalers - exceptionally high turnover given the breadth of vehicles using this cap, and a routine wear item recommended for replacement every few years.

Repair Shops - tested unit reduces comeback risk on a common cooling system repair.

Distributors - private label packaging available for building a branded catalog.

End Customers - restored cooling system pressure and reduced overheating risk.

Packaging & Shipping

Standard export cartons. Customized packaging available for distributor branding. OEM-style and private label printing on request. Container loading handled directly, with mixed-SKU consolidation for smaller orders. Worldwide shipping to Europe, North America, South America, the Middle East, Africa, and Southeast Asia.

Why Choose GSK Auto

GSK Auto manufactures factory-direct, keeping pricing tied to production cost. This expansion tank cap is built to OEM specification and tested before packing. We support low MOQ, private label packaging, and worldwide shipping, with our technical team available to confirm fitment before you order.

Call to Action

Sourcing coolant expansion tank caps for BMW's 5, 6, 7, 8 Series, M3, M4, M5, X5, or X6? Contact GSK Auto for a wholesale quote, catalog, or OEM/private label cooperation.