Q: Top water hose gets hot with new thermostat

Hello. This is completely normal operation of the vehicle’s cooling system. The top radiator hose should always be warmer than the bottom. As coolant flows through the water pockets in the engine it picks up heat, and it is then transferred back into the radiator through the top hose. The coolant is cooled off in the radiator and then is recycled back into the engine through the lower radiator hose. Hence, hot on top, cold on bottom. If your symptoms were opposite, you would have more serious issues. The thermostat’s job is to hold the coolant in place until the engine is warm enough to need allow the flow of coolant through the system. Once the engine is warm enough to warrant coolant flow, the thermostat opens to a degree corresponding to the engine temperature.