No thermostat but you do need to slow the flow down so that it remains in the block long enough to absorb the heat and stay in the rad long enough to dissipate the heat. That's where a restrictor comes into play. Moroso sells a kit with different sizes but 3/4" is a good starting point.

In the pits during cooldown between rounds, using an electric water pump and a thermostat to cool the engine doesn't always work. As the coolant temp decreases, the thermostat closes and coolant flow stops going through the rad. A simple fix is to drill a couple of small holes around the thermostat which will still allow some flow through the rad even if the thermostat is closed.