3gmd overheating history

[hornby sailor]

checking out a boat nest week with yanmar mechanic. last year a reported overheat, po says she shut it down and got it fixed, blocked riser? new thermostat and impellor and motored lots afterwards says she observed the temp rising on guage, shut down before warning buzzer. her mechanic told me it seemed like she overheated the block pretty good. what tests should i do. how does one troll for filings with a magnet in the oil pan?

[hornby sailor]

1981 raw water 3gmd