Has acyl-CoA thioesterase activity towards long-chain (C16 and C18) fatty acyl-CoA substrates, with a preference for linoleoyl-CoA and other unsaturated long-chain fatty acid-CoA esters (By similarity). Plays an important role in mitochondrial fatty acid metabolism, and in remodeling of the mitochondrial lipid cardiolipin (PubMed:22586271). Required for normal mitochondrial function (PubMed:22586271). H2O + hexadecanoyl-CoA = CoA + H(+) + hexadecanoate (9Z,12Z)-octadecadienoyl-CoA + H2O = (9Z,12Z)-octadecadienoate + CoA + H(+) H2O + tetradecanoyl-CoA = CoA + H(+) + tetradecanoate (9Z)-octadecenoyl-CoA + H2O = (9Z)-octadecenoate + CoA + H(+) (9Z)-hexadecenoyl-CoA + H2O = (9Z)-hexadecenoate + CoA + H(+) (5Z,8Z,11Z,14Z)-eicosatetraenoyl-CoA + H2O = (5Z,8Z,11Z,14Z)-eicosatetraenoate + CoA + H(+) H2O + octadecanoyl-CoA = CoA + H(+) + octadecanoate Homodimer. With increasing age, mice develop fatty liver, due to impaired mitochondrial fatty acid metabolism, and impaired remodeling of the mitochondrial lipid cardiolipin. Mitochondria contain increased levels of monolysocardiolipin, and decreased levels of linoleic and linolenic acid. The altered fatty acid metabolism leads to decreased mitochondrial beta-oxidation and ketone body formation. Mitochondria show abnormal, elongated morphology, and their function is impaired. Belongs to the THEM4/THEM5 thioesterase family.