Very easy to do. This is how I've don't it in the past. Drain coolant from radiator ,engine block and where ever you can. Fill with water and some dawn soap if coolant is nasty. Start truck and get up to operating temp for 10-15 min. Shut off Drain water. Fill again with just water and run for a bit. Drain again and open cock on bottom of radiator and fill with water and start truck and let it run and cycle water through system. Let it keep draining during this time. Then change thermostat and fill with coolant and you should be good. That's how I've done it in trucks gas/diesel farm equipment and heavy equipment. Never had any issues.
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