Troubleshooting an overheating engine

After steam started coming out of the exhaust, followed by a high temp engine alarm, It’s time to start troubleshooting the raw water side of a Yanmar 2GM20F engine. I take a look at the raw water strainter, raw water pump, heat exhanger, antisiphon valve and the exhaust mixing elbow. I don’t think the problem was just one thing, but a few things compounded together. One of the splines was missing on the impellor, another was cracked, and the heat exchanger was heavily scaled and partially blocked.