merely a sleeve. Advantages of wet liners are a lower mass, reduced space requirements, and coolant being heated faster from a cold start, which reduces start-up fuel consumption and provides heating for the car cabin sooner. Dry liner cylinder blocks use either the block's material or a discrete liner inserted into the block to form the backbone of the cylinder wall. Additional sleeves are inserted within, which remain "dry" on their outside, surrounded by the block's material. For either wet or dry liner designs, the liners (or sleeves) can be replaced, potentially allowing an engine overhaul or rebuild without replacing the block itself, although this is often not a practical repair option. Coolant and oil passages Crankcase The crankcase is the structure that houses the crankshaft. As with cylinder blocks, this is primarily an integrated component in modern engines. Materials Engine blocks are normally cast from either cast iron or an aluminium alloy. Aluminium blocks are much lighter in weight and transfer heat more effectively to coolant, but iron blocks retain some advantages, such as durability and reduced thermal expansion. Monoblocs An engine where all the cylinders share a common block is called a monobloc engine. Most modern engines use a monobloc design of some type, and few modern engines have a separate block for each cylinder. This has led to the term "engine block" usually implying a monobloc design, with "monobloc" itself rarely being used. In the early years of the internal combustion engine, casting technology couldn't produce large castings with complex internal cores (for water jackets etc). Most early engines, particularly those with more than four cylinders, had their cylinders cast as pairs or triplets of cylinders, then bolted to a separate crankcase. As casting techniques improved, an entire cylinder block of 4, 6, or 8 cylinders could be produced in one piece. This monobloc construction was simpler and more cost-effective to produce. For straight engine cylinder layouts, this meant that all the cylinders, plus the crankcase, could be produced in a single component. One of the early engines produced using this method is the 4-cylinder engine in the Ford Model T, introduced in 1908. The method spread to straight-six engines and was commonly used by the mid-1920s. Up until the 1930s, most V engines retained a separate block casting for each cylinder bank, with both bolted onto a common crankcase (itself a separate casting). For economy, some