Water not circulating through top hose

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.

drain the coolant from radiator remove upper hose from thermostat housing clean housing and block install new thermostat with the spring end toward the block pointed to radiator use a new gasket and a small amount of gasket sealer when tightning the bolts back on the thermostat housing be sur to run them down evenly or you will crack the housing reinstall hose add coolant start and check for leaks

the side without the spring towards the rubber hose/rad

Do you know if the radiator is full of coolant ?
Does the gauge on the dash show the engine temp to be cold after you run the engine ?
Could be the thermostat is not closing.
If the heater hoses are getting hot, could be a blend door problem under the dash.

Thermostat REMOVAL & INSTALLATION CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old. E-Series Engines NOTE: The engine thermostat is housed in the water outlet casting on the cylinder head.

1. Open the draincock on the radiator and drain the coolant into a suitable drain pan.
2. Remove the upper radiator hose from the water outlet side and remove the bolts securing the water outlet to the cylinder head.
3. On E16 models, remove the exhaust air induction tube clamp bolts, then the water outlet bolts.
4. Remove the water outlet and thermostat. To install:
   
5. Clean off the old gasket from the mating surfaces with a razor blade or equivalent.
6. When installing the thermostat, be sure to install a new gasket and be sure the air bleed hole in the thermostat is facing the left side (or upward) of the engine and that the spring is toward the inside of the engine. Also make sure that the new thermostat to be installed is equipped with an air bleed hole.

CA16DE, CA18DE and GA16i Engines Fig. 1: Always make certain the jiggle valve is facing upward when installing the thermostat

1. Disconnect the negative (-) battery cable and drain the coolant from the radiator and the left side draincocks on the cylinder block.
2. On GA16i engines, disconnect the water temperature switch connector from the thermostat housing.
3. Remove the radiator hose from the water outlet side and remove the bolts securing the water outlet to the cylinder head.
4. Remove the thermostat and clean off the old gasket or sealant from the mating surfaces. To install:
   
5. Install the thermostat with a new gasket. When installing the thermostat, be sure to install a new gasket or sealant and be sure the air bleed hole in the thermostat is facing the left side or upward on the engine. The jiggle valve must always face up. Also make sure the new thermostat to be installed is equipped with an a ir bleed hole. Some thermostats have the word TOP stamped next to the jiggle valve. Again, the word TOP and the jiggle valve must be facing up. NOTE: When using RTV sealant instead of gaskets, make sure the surface you are working on is very clean before applying the sealant, then apply an even bead. Allow the RTV to dry slightly to form a thin skin. The component MUST be tightened before the RTV dries completely. The bolt torque should be checked again after RTV has completely dried.
   
6. Install the water outlet and upper radiator hose.
7. On GA16i engines, connect the water temperature switch connector to the thermostat housing.
8. Fill the cooling system and connect the negative (-) battery cable.
9. Bleed the cooling system as outlined in this section.

1.6L (GA16DE) and 2.0L (SR20DE) Engines Fig. 2: Thermostat and housing — SR20DE engine
Fig. 3: Thermostat and housing — GA16DE engine
Fig. 4: Always make certain the jiggle valve is on the top side — GA16DE engine shown NOTE: The thermostat is housed in the water outlet casting on the cylinder head on most models. On the GA16DE engines, the thermostat is housed in the water outlet casting attached to the water pump.

1. Disconnect the negative (-) battery cable.
2. When cool, open the draincock on the radiator and drain the coolant into a suitable drain pan.
3. Remove the upper radiator hose from the water outlet side and remove the bolts securing the water outlet to the cylinder head and any other components in the way.
4. Remove the water outlet and thermostat. To install:
   
5. Clean off the old gasket from the mating surfaces of the thermostat housing and engine block. NOTE: When using RTV sealant instead of gaskets, make sure the surface you are working on is very clean before applying the sealant, then apply an even bead. Allow the RTV to dry slightly to form a thin skin. The component MUST be tightened before the RTV dries completely. The bolt torque should be checked again after RTV has completely dried.
   
6. When installing the thermostat, be sure to install a new gasket and be sure the air bleed hole in the thermostat is facing upward and that the spring is toward the inside of the engine.
7. Install the water outlet and tighten the bolts.
   • GA16DE — 13–16 ft. lbs. (18–22 Nm)
   • SR20DE — 60–72 inch lbs. (6–8 Nm)
8. Install the remaining components in the reverse order of removal.

the water pump and thermostat should have solved it. an air pocket can cause that but usually not to that degree.

don't get one of those cheap *** plastic impeller water pump for sissies. Get the metal impeller one. get a cool running thermostat and drill two 3/16" holes in it 180 degreess from each other. you may have installed the t-stat backwards.

follow the top radiator hose from the radiator to the engine, the spout the hose hooks to on the engine is the thermostat housing, you unbolt it, pull the old thermostat out, clean the joining surface of the thermo housing and the engine block of debri (old gasket) install new thermostat making sure the spring mechanism on thermostat is installed towards the engine, put the new gasket in place and reinstall the thermostat housing.

Explorer Thermostat LocationHere is advice for finding the thermostat:

• Follow the upper radiator hose from the radiator to the engine and there is a housing that houses the thermostat. Take it off and when you reinstall the thermostsat, make sure the spring goes toward the engine.

• The thermostat is located on the motor block under the three bolt flang that the top rediator hose connects to. Remove the three 10MM bolts and the thermostat can be removed for replacement.

How to Change an Explorer Thermostat

• 1. Remove the air cleaner air duct from the throttle body and air cleaner.
• 2. Follow the upper radiator hose to the engine to locate the thermostat housing. The housing is located at the front of the intake manifold.
• 3. Loosen the hose clamp, then detach the hose from the fitting. This can be difficult. If it's stuck, grasp with a pair of adjustable pliers and twist to break the seal. Then pull it off.
• 4. Remove the bolts and detach the housing cover. Be prepared some coolant may leak out as the gasket seal is broken. Remove the thermostat.
• 5. Install the new o-ring onto the thermostat (no gasket is needed) and install the thermostat into the intake manifold with the spring side pointing toward the engine.
• 6. Make sure the air release valve is in the up 12 o'clock position. Install housing cover and bolts. Reattach the hose fitting and tighten the hose clamp. Fill the cooling system with a 50/50 mix of coolant and water, and burp the system.

Follow the upper radiator hose back to the engine until you see a hose clamp holding it to the engine block. This is the thermostat housing and should have bolts to pull it apart. The new thermostat installs with the spring toward the engine. When purchasing a thermostat, if you get one with a jiggle valve (a little piece of metal on the top that jiggles) it'll help you orient the new thermostat as the jiggle valve goes on top (the thermostat and housing aren't perfectly round so you have to rotate it until the thermostat fits into the housing correctly). You can use some spray adhesive to keep the gasket in place while installing the thermostat. This helps, but it not necessary.

check to see if you are getting heat through the heater and then check and test your thermostat, if you require further assistance let me know. if this helps please take the time t rate this siote. and good luck.