Audi Coolant Expansion Tank - Rein 8K0121405P

Product Information

The engine coolant reservoir, also known as an ‘overflow bottle’ is a crucial component of modern vehicle cooling systems. Its job is to capture the increased volume of engine coolant that is created as the coolant is heated and expands. It needs someplace to go, so a coolant line that typically runs from the radiator outlet to the top of the engine coolant reservoir will feed the reservoir, while the reservoir feeds the engine as it needs more coolant to send through the engine and back through the radiator.

Engine coolant reservoirs are typically made of plastic and can be either clear or opaque. Some performance or aftermarket overflow bottles are made of aluminum or other more durable materials.

• Fogging: Over time, due to chemical exposure, age, and heat cycles, the clear plastic used in most engine coolant reservoirs can become foggy and opaque. This can make it difficult to read the coolant level accurately.
• Leaks/ Cracking: The most common area for an engine coolant reservoir to leak is usually at a plastic seam or seal. As the bottle is run through thousands of heat cycles, from ambient temperatures below freezing to 200 degrees Fahrenheit plus, the weakest part of the reservoir, usually a seam or molded junction, can crack and fail.
• Age: Over time, due to age and exposure, the plastic and materials will become brittle and prone to cracking and other age-related failures.
• Coolant leaks: The most common failure of a bad engine coolant reservoir is a coolant leak. This can be slow or minimal, or it can be a total instant failure of the reservoir. If you notice a slow coolant leak and can diagnose it back to the overflow bottle, or coolant reservoir, it is recommended to replace it asap.
• Overheating: A bad engine coolant reservoir can reduce engine cooling system pressure, reducing the effective boiling point of the engine coolant. Depending on temperatures and conditions, this can result in engine overheating.

About Rein

Founded in 2007, CRP Automotive introduced the Rein Automotive line of OE-quality replacement parts to the aftermarket. And in just two short years, Rein Automotive has become very popular among both warehouse distributors and professional repair technicians. Rein is the German word for “pure”, and has come to be synonymous with quality in the automotive aftermarket. A true dealer alternative.

The Rein brand includes a growing number of “better than OE” parts for selected applications. These parts address known weaknesses and premature failures of factory parts. Many of these replacement and service solutions have been developed with the help of our Innovation Council, a hand-picked group of experienced professional repair technicians and shop owners throughout North America.

All Rein Automotive OE-quality parts are backed by the CRP Automotive standard, and are backed with a ISO 9001:2015 quality management system certification. Each year, CRP Automotive ships thousands of Rein Automotive brand products. And with widespread NAFTA market distribution through strategically placed warehouses in Cranbury, New Jersey and Puebla, Mexico - OE-quality products like Rein Automotive are delivered to customers both faster and more cost-effectively than ever before.

In 2017 Rein partnered with FCP Euro in competing a W204 C300 AER car for the 2017 season. The partnership focused FCP Euro to dive deep into the Rein catalog offering, and hundreds of new products were added and integrated into our catalog. Hundreds of new packages were created not only using the full part pine up of Rein products, but also the entire family of CRP products like Pentosin.

Rein is also an innovative brand, winning numerous trade awards — including multiple new product innovation awards at the annual AAPEX trade show.