Unless you are a bit of a masochist and like swapping water pumps, it is a good idea whenever you swap engines to put a new water pump and thermostat on the new engine. It is cheap insurance for long-term reliable service. We went with a high-flow water pump from 4WD Hardware and a high-flow 195-degree thermostat that we sourced from Summit Racing. Be careful when you order your parts. Double-check them closely when they show up. There is only one number separating a Cherokee/Comanche pump and a TJ pump. Any wrong parts can quickly trip up a tight weekend swap schedule like this.