page_title: Expansion tank
section_title: Automotive applications
hierarchical_section_title: Expansion tank / Automotive applications
caption_attribution_description: SAAB H engine in a 1987 Saab 90
context_page_description: An expansion tank or expansion vessel is a small tank used to protect closed water heating systems and domestic hot water systems from excessive pressure. The tank is partially filled with air, whose compressibility cushions shock caused by water hammer and absorbs excess water pressure caused by thermal expansion.
context_section_description: An expansion tank, also known as "overflow bottle", is also used in the cooling system of most internal combustion engines, to allow the coolant, the antifreeze, and the air in the system to expand with rising temperature and pressure. The tank is also called a "coolant recovery tank", since it prevents venting and permanent loss of coolant, by allowing it to be sucked back into the cooling system as the engine cools.
caption: Expansion tank in a 1987 Saab 90 (brown plastic tank with white lid at top of picture)
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