Catalyzes the hydrolysis of acyl-CoAs into free fatty acids and coenzyme A (CoASH), regulating their respective intracellular levels (PubMed:16934754, PubMed:19170545). Has acyl-CoA thioesterase activity towards medium (C12) and long-chain (C18) fatty acyl-CoA substrates (By similarity) (PubMed:16934754, PubMed:19170545). Can also hydrolyze 3-hydroxyphenylacetyl-CoA and 3,4-dihydroxyphenylacetyl-CoA (in vitro) (By similarity) (PubMed:16934754, PubMed:19170545). May play a role in controlling adaptive thermogenesis (By similarity). {ECO:0000250|UniProtKB:Q9CQR4, ECO:0000269|PubMed:16934754, ECO:0000269|PubMed:19170545}. This is the function of ACOT13 (acyl-CoA thioesterase 13, Ensembl gene identifier ENSG00000112304).