 The 7 gal (32 l) oil tank was built into the forward, port centre section.Early "K" serialled Mk Is were powered by the 1,029 hp (768 kW) Rolls-Royce Merlin C engine; from the "L" serial numbers the later Merlin II of 1,030 hp (768 kW) was installed.The main coolant radiator was housed in a fairing under the rear wing centre-section; the oil cooler was also incorporated into the main radiator.