An oil cooler (1) is removably mounted on the side of an engine block (13) with a tubular coolant flow coupling (19) received as a push-fit in an aperture (18) in the block so that the coolant flow connection is simply made as the oil cooler is fastened to the side of the block. The coupling (19) may be a push-fit in respective axially aligned apertures (18, 20) in the block and the cooler. The flow coupling may be an inlet coupling for coolant from the block. The end of the coupling that cooperates with the block has an extension (24) that projects into a coolant flow passage (17) in the block and is shaped to form an inlet opening that is directed laterally of the axis of the coupling and upstream of the coolant flow in said passage. The extension (24) collects coolant from said passage and produces a pressure drop in said passage. A coolant return-flow coupling (28) is provided between the oil cooler (1) and the block (13) and opens into said passage (17) downstream of said inlet coupling (19) so that said pressure drop assists the flow of coolant through the cooler.
