Expansion Tank - BMW 335d

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 Mahle Behr

Mahle Behr GmbH & Co. KG is a German corporation active in the automobile industry, headquartered in Stuttgart-Feuerbach. It is a specialist for automotive air conditioning and engine cooling systems. Mahle began in 1920 when pistons made of heavy gray cast iron were being used in internal combustion engines for automobiles and there was a need for a new design. The Mahle brothers countered this trend by producing light-alloy pistons at their small, newly established company however the technology was still finicky and problems come up frequently. They soon determined that they needed to come up with a solution to keep dirt and dust out of the engine so they eventually developed air and oil filters as well. Their perseverance paid off and the light-alloy pistons began to take over the market. Today, half of all automobiles produced worldwide contain MAHLE components. MAHLE offers an extensive range of parts for everyone including pistons, cylinder liners, piston ring sets, bearings, assemblies, valves, valve train components, and air, oil, fuel, and cabin air filters. Their catalog and online database of aftermarket engine components is an indispensable reference.In early 2016, Stuttgart-based MAHLE GmbH increased its holding in the Behr Group from 36.85 percent to approximately 51 percent with the acquisition of all shares in the BWK GmbH holding company. The company now goes by Mahle-Behr.

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