2006 coupe AT. Replaced radiator, no leaks at idle, temp range normal, hot cabin heat, but lower radiator hose cold.

Few weeks back, car overheated and dumped all the coolant, about 30 seconds from home. Pulled over, waited a bit, then drove it home. Was at top temp for ~10 seconds.

found a bunch of fluid dumping out of the top of the radiator on the passenger side. Figured the plastic top had cracked went I ran over a particularly tall parking lot curb earlier that day. Replaced the radiator and burped the system. Car has the front end jacked up, used the lisle no spill funnel, made sure to release air from the back heater hose cap, ran for 20+ mins, cabin air hot, fans spinning. Yet the lower radiator hose is stone cold.

Is this likely a thermostat? Something else? Maybe the water pump? Is there an easy way to check the water pump? Oil isn’t milky, so I don’t think I blew a head gasket.

 

Pumps don't typically have catastrophic failues, they usually just wear out very slowly over a long long time.

Thermostat on the other hand, they die rapidly when people use regular water in the system instead of distilled+Nissan coolant.

First thing is to pressure test the system to ensure it's actually holding pressure.

There's a REALLY good chance there's just an air bubble on the back side of the thermostat, I've switched over to using a coolant airvac system to fill coolant but the MOST IMPORTANT THING is to add coolant VERY VERY slowly (unless using the airvac). You should be pouring in coolant at a rate of no more than 1 gallon per minute. Not "dump in 1 gallon and wait 1 minute", the flow rate needs to be NO MORE than 1 gal/minute or the bubbles get trapped behind the coolant pouring in.

The airvac has been super easy though, suck the system down to -20psi or as far as your air compressor will take it. Suck in coolant. open the heater core purge valve a little to make sure it's solid coolant, heat cycle the car with a spill free funnel, win.