Brand new thermostat housing arrived without plug.

[2004mountaineers]

Brand new thermostat housing arrived without plug, as shown
in below pictures. I have the old plug and its spring-clip, but
it sets down into the hole of the new thermostat housing very loosely.
Also, I notice there is no O-ring at the top of the old plug.
Any advice ?

The old plug is much looser in the new housing than in the old
housing.

The old plug seemed to be where fluid was leaking from in the old
housing; so, I probably did all that work for nothing.

Will RTV solve this whole problem ?

Edit: Also, how many inch-pounds of torque should be applied to
the three 10mm bolts that hold the thermostat in ? Videos say
89-inch-pounds for the three 8mm thermostat housing bolts but
don't say anything about the three thermostat bolts.

https://imgdump5.novarata.net/pyw4pz.jpg

2004 Mercury Mountaineer, 4liter v6, 'awd'.

 

[2004mountaineers]

Well, I applied a generous amount of Permatex 81180 (500F) as shown below. But,
I doubt it will be leak-proof, given how ridiculously loose the plug fits in the hole.

https://imgdump5.novarata.net/j57b5j.jpg

 

[2004mountaineers]

Another thing I noticed: On both the old housing/sensor and the new housing/sensor,
I can easily spin the sensor with just two fingers. How is that EVER supposed to be leak-proof ?

 

[leadfootdriver]

My new Sensor moves freely also. It does not leak..

 

[2004mountaineers]

Well, with about 1.2gallons of coolant removed, it held 15psi for 10minutes. So, I guess
it is air-tight, surprisingly.
At steady-state, the temp-gage reads two notches lower than middle, even though I
re-used the old thermostat. So, I guess the new temp-sensor may be off in its reading ?
After a full hour of trying to purge the system of air with leak-free funnel, the fluid
level in the reservoir is still about 0.9inches above the top-line, where it was before. So,
I somehow have that much air trapped in the system somewhere and can't get it out,
because I only put the same coolant in that I removed -> air in system somewhere.

EDIT: UNLESS the engine being non-cold is why the coolant level is reading high. I
will let it cool down for about 11hours and then look at it again.

 

[2004mountaineers]

Yep, after the engine cooled down, the coolant level came back to the line.
Except for the issue that the steady-state gage reading is two marks left of
center (presumably due to off temp sensor), job is completed. I guess
I could try swapping the old temp-sensor back in, but not at this time.
Temp gage will just have to be off for a while.
Total cost: $18.26 (amazon).