Been under the weather for a week now and going stir crazy :( We have also had 90km/hr winds howling by our house along with heavy rain at times.

Wife went out, so despite her instructions to forget about the car until I am better, I went out and finished job (car is in garage)

I had front of car jacked up and temperature switch out of tstat housing. Just filled through overflow tank until a/f gurgled out of switch socket. Screwed temp switch back in. Ran engine for a while. No leaks, no belt noise!
Took car for short drive to get fully up to temperature with heater blasting. Heater worked well, no change in coolant level and no leaks.

Summary: This job started out as - find the mystery noise. That turned out to be alt belt slipping. Changed belts. Noise gone. BUT, noticed AF dripping on belt from tstat housing. Drained rad and changed tstat and seal, but found pitting in casting. JBweld fixed that. Re-installed rad plug, but broke it :( Bought a couple of spares and finished job today!

Back indoors trying to shake off flu.

PS: I have the FSM but don't have a torque wrench that can measure 1.5-2 Nm!

As for torque setting... I use a 1/4" ratchet and grip only the head. Tighten that way then push a bit on the handle.

Just use a coin to tighten the radiator drain plug. That's all you need.

The FSM says that, but then also specifies the torque!

After breaking the old plug using a large screwdriver, I tightened the new one with my thumbnail!

Those plugs get brittle from heat, I guess. According to Dupont, if they used modern engineered plastics like Zytel, they would last for 3000hrs. Sounds like we should be changing the plug each time system is flushed or say every 150k miles.

if that plug is getting hot... there's something wrong with your engine or cooling system... the lower tank should have the coldest coolant. often ambient temp...

Nothing wrong with my engine or cooling system that I know of!

For a rad to work, it needs a substantial temperature difference between coolant and incoming ambient air at both inlet and outlet. Temperature drop of coolant across a rad would likely be in the 10-30F range. Say 20F on average. So if hot coolant is at 180F, then bottom of rad would be at about 160F.

160F is still pretty HOT!

Above is theoretical based on some guesses of heat load and coolant flow. It would be interesting to measure actual temperature using an IR gauge.

That's normally true, but the 617 uses a high capacity bypass system. Only a small amount of coolant is sent to the radiator, and the output back to the engine is barely warm. When the system is at full capacity, then the bottom of the radiator would be warmer. On my signature car, I can hold on to the return elbow going back to the t-stat housing on all but the hottest days.