Catalyzes the hydrolysis of acyl-CoAs into free fatty acids and coenzyme A (CoASH), regulating their respective intracellular levels (PubMed:19405909). Has acyl-CoA thioesterase activity towards medium (C12) and long-chain (C18) fatty acyl-CoA substrates (PubMed:19405909). Can also hydrolyze 3-hydroxyphenylacetyl-CoA and 3,4-dihydroxyphenylacetyl-CoA (in vitro) (By similarity). May play a role in controlling adaptive thermogenesis (PubMed:24072708). a fatty acyl-CoA + H2O = a fatty acid + CoA + H(+) decanoyl-CoA + H2O = CoA + decanoate + H(+) H2O + octanoyl-CoA = CoA + H(+) + octanoate butanoyl-CoA + H2O = butanoate + CoA + H(+) H2O + hexanoyl-CoA = CoA + H(+) + hexanoate H2O + tetradecanoyl-CoA = CoA + H(+) + tetradecanoate H2O + hexadecanoyl-CoA = CoA + H(+) + hexadecanoate dodecanoyl-CoA + H2O = CoA + dodecanoate + H(+) (9Z)-octadecenoyl-CoA + H2O = (9Z)-octadecenoate + CoA + H(+) kcat is 3 sec(-1) for hexanoyl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). kcat is 5 sec(-1) for decanoyl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). kcat is 3 sec(-1) for dodecanoyl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). kcat is 4 sec(-1) for tetradecanoyl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). kcat is 3 sec(-1) for tetradecanoyl-CoA hydrolase activity (at 25 degrees Celsius) (PubMed:19405909). kcat is 6 sec(-1) for tetradecanoyl-CoA hydrolase activity (at 50 degrees Celsius) (PubMed:19405909). kcat is 3 sec(-1) for hexadecanoyl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). kcat is 6 sec(-1) for (9Z)-octadecenoyl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). kcat is 4 sec(-1) for beta-hydroxybutyryl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). kcat is 7 sec(-1) for (3S)-hydroxy-3-methylglutaryl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). kcat is 1 sec(-1) for malonyl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). kcat is 1 sec(-1) for phenylacetyl-CoA hydrolase activity (at 37 degrees Celsius) (PubMed:19405909). Homotetramer. Interacts with PCTP. During interphase, found both in the nucleus and in the cytoplasm. At mitosis, localizes to the spindle. Colocalizes with tubulin. Highly expressed in the kidney and moderately in the heart, liver, brain, small and large intestine. Also expressed in brown adipose tissue. No visible phenotype until 7 weeks of age. Animals are viable and fertile. After 7 weeks, mutant mice exhibit a modest decrease in body weight and decreased adiposity, compared to wild-type animals, despite increased food consumption. They tend to show a reduced hepatic fatty acyl-CoA thioesterase activity, leading to alterations in fatty acid metabolism and improved glucose homeostasis. When fed a high-fat diet, mutant livers are protected against steatosis and increased hepatic glucose production (PubMed:22345407). Mutant mice adapt more rapidly than wild-type to short-term cold exposure by increasing physical activity, food consumption and energy expenditure. After 96-hour equilibration at cold temperature, genotype-dependent differences are abolished. Mutant brown adipose tissue show reduced lipid droplets, alterations in the ultrastructure of mitochondria and a small increase in the expression of thermogenic genes (PubMed:24072708). Belongs to the thioesterase PaaI family.