Cleveland engines have the thermostat in the front of the block, unlike the 351 Windsor, which has the thermostat in the manifold. Coolant exits the heads, goes through the block, and out to the radiator so the intake manifold stays "dry". This steel plate acts as a timing chain cover; the factory water pump bolts directly to it. These plates usually crack and corrode over time. Summit Racing offers a laser-cut steel replacement. Make sure to use the factory brass restrictor plate underneath the thermostat to help prevent overheating issues.