The procedure outlined in the service manual is very sketchy to say at least.
So I got a chance to practice it on the wrecking yard on the car without front end damage to make sure it is doable at home without extensive efforts. The main obstacle during this simple repair is to move a wire harness channel far enough to see the working area (I moved it almost 2 inches). It is particularly important because form in place gasket is used between coolant outlet housing and a cylinder head.
I am presenting procedure written based on hands-on experience (except the coolant outlet installation)
Before starting I've had:

• Battery removed (may not be needed)
• Air cleaner housing removed
• Radiator drained (about 1 liter of coolant)

All fasteners require 10 mm socket wrench

Per this procedure both radiator houses are staying attached while heater supply hose and throttle body coolant supply hoses are removed

1) Place 2 liter catch pan under the fitting; disconnect the heater supply hose at firewall

2) Drain the coolant




3) Unbolt harness channel bracket from the head (10 mm socket)



4) Unbolt harness ground terminal (10 mm socket)
5) Unbolt harness bracket from manifold (10 mm wrench)



6) Disconnect engine wire loom from the bracket



7) Separate ignition coil harness from the support bar (arrow)




8) Remove C103 shorting bar from the steel bracket
9) Disconnect coolant supply hose from throttle body
10) Unbolt A/T Line solenoid harness screw (10 mm socket) and separate harness from the metal bar. Pull out 2 wire bundles from the harness channel


11) Move harness channel about 2 inches away from the head and lift it up about ½ inch



12) Remove 4 screws (10 mm socket) attaching coolant outlet housing to the head



13) Remove thermostat and clean the mating surfaces

14) Place a new thermostat in the head

15) Apply sealant to the outlet housing (Ultra blue Permatex, Toyota form in place black gasket maker, or equivalent)

16) Install housing and tighten 4 mounting screws

17) Connect the heater hose; wait 30 minutes

18) Add coolant via filler neck and disconnected throttle body hose, then attach the hose to the throttle body

19) Pressure test system (10 psi for 15 minutes) and check for leaks at the joint between the outlet housing and head

20) Reinstall wire harnesses and mounting screws

21) Reinstall air cleaner (and battery)

22) Start the engine, bleed the air and check for leaks

 

Hi Doctor J,
Fantastic write-up! Thanks for taking care to photo and label the steps...very helpful. In doing the process, probably will replace all hoses. In your second photo, steps 4 & 5, do you know what is the hose shown there? Looks like a short hose, maybe 4" long +/-, curved about 90 degrees from one end to the other. Is it also a water hose? Looks like it may be just under the air intake....

 

Coolant hose (throttle body-return)
The installation of the harness bracket screw is challenging and may require use of magnetized socket
(another photo shows its location)

I took these photos when changing coolant (2x radiator drain and refill), was overdue by 1 year