In the winter. But keep in mind he's talking about a stuck open t stat. Flow will be restricted somewhat. If you just removed the t stat on a D1 it would more than likely overheat.
A stuck open thermostat will cause overheating? Really? The ONLY purpose for a thermostat in a water-cooled, internal combustion engine like in a DII is to regulate the MINIMUM operating temp. It blocks or restricts coolant temp until its specified temp is reached. IT DOES NOTHING to manage temps above its operating range! Two people weighing in on one thread with completely bass-ackward opinions. Sheesh! This isn't rocket science!