Runs hot sometimes. Top radiator hose hot, bottom cold. What's wrong?

It would have been useful to know where the hose from the tee goes and what diameter as that is new to me. 50 years as a repairer and I have never seen a top radiator hose with a tee branch.

Usually the engine heats and the thermostat opens and starts coolant circulating through the radiator, up the bottom hose into the water pump to be pushed round again.
The volume of coolant moved by the water pump, even at idle should be far in excess of that circulating through the heater matrix ensuring adequate circulation through the radiator as soon as the thermostat opens.

The top hose must be hot because the thermostat is open so why doesn't the coolant go further and heat either the branch or the rest of the hose and radiator...
Sometimes a pump with a plastic impeller will lose a vane and overheating due to insufficient circulation is likely.

Other things are more common - semi-blocked radiator tubes restricting coolant flow.
Silt build up in the cylinder block causing hot spots in the cylinder walls.
Restricted air flow through the radiator.
Electric coolant fan not working.
Excess combustion gas in the cooling system interfering with thermostat operation.
Degassing system blocked with the same result.

If you changed the water pump and thermostat, all i can suggest is a very clogged radiator, assuming the coolant is at proper capacity and mixture, plus no air pockets no motor

Did you put the thermostat in backwards? If you did, it wont open when hot. Thermostats look pretty much the same - with some minor variations. It's important to note the the side with the spring should be facing the (hot) engine and the other side facing the (cool) radiator as shown in the image below. If the spring side doesn't get hot - it won't open to let hot water from the engine flow to the radiator for proper cooling.

this sounds like a coolant flow problem. possible rad plugged or water pump problem.

HI Anon.
Remove your radiator cap (WHEN ENGINE IS COLD), run the motor and let it warm up a minute or two, have someone rev the engine a little while looking into the radiator. If the water goes down and/or you see the water moving, your water pump is good. If not this means that your water pump is bad and is not moving enough water through the system. Try Removing your thermostat and run the engine without it. Keep checking the radiator hoses to see if they are the same temperature. If they are not the same temperature the water pump is bad. If they are the same temperature your thermostat is more than likely the culprit. Hope this helps.

Thermostat temperature senecer needs to be replaced

could be you fitted the thermostat in the wrong way around ,or the plastic impeller on the water pump with a steel drive shaft has failed they end up with the drive shaft spinning but the impeller is not turning ,go for the thermostat first though .

it may be a little off, but the lower water hose seldom gets very hot,, as its this hose that suplyes the engine with ""cold water"" the hot water comes out the top hose,, drains down the rad and cools on the way down then enters the engine through the bottom hose """if your engine stayes running in the normal place on the gage,,,and not over heating""" why are you spending money for nothing???""
you wont get the bottom hose to run hot unless the engine is cooking

Sounds like the water pump.Check if you see coolant or coolant residue behind the water pump pulley.

Hi, I think you have an airlock in the pump,You need to drain the water totaly when stone cold.Drain radiator and disconect hoses from waterpump and top hose from themostat. Reconect pump hose and add water slowly into radiator through top hose untill rad is full then squeeze bottom hose vigourously,You ll feel the water tension in the hose, Connect all hoses and top up water level. This must be done cold as hot and cold water will cause an airlock. Hope this helps you out.All the best.Phil