I have gotten some great response from several of you ....but no bottom line found..

I have made numerous phone calls to Dayco all over the world and they no longer handle thermostats there are a few left in Australia but the freight charge is prohibitive
Their corporate office says they are working on getting them back but it's a minimum of six months away

The Tridon is also only available in Australia

So we have the Gates possibility...what is difference between their 33188 and their 33188S???

Some more feedback ...has anyone tested the Gates? Which one? Was a hole needed to be drilled....
Hopefully we are getting close to solving a long felt pain in the Southside for Jag lovers

 

I just put in the Gates, and it does need a small hole drilled, I used 5/64" drill. I tested it in a pan of hot water and it does move enough when hot to block off the bypass. It has not been hot outside enough yet for me to determine if it makes a major difference, but the temp gauge does sit lower then it did with the previous OEM Waxstats.

The difference between the S and non S is the spring and wax motor. See the description of it here: https://www.rockauto.com/en/moreinfo...366269&jsn=262 On Rockauto the difference in price was less than 10 cents, so I went with the S version.

 

Easy to send a Tridon over to you. (I am presuming it has the same Thermo as the 5.3L)

 

Buy a Stant Superstat and drill a small hole in it about half an inch inside the rim:

 

Just checked out the Stant Superstat 45398 that Greg suggested......They do list this for the v12 6L....as well as many other vehicles and it has great reviews.
It has a nonlinear v notch to expel air ...so it should not need a hole drilled for that purpose
Has anyone actually used this and what is consensus on hole or no hole???
BTW...my heater has stopped putting out heat during all this.
My coolant has all leaked out over this long down time. I ordered a new heater check valve for the firewall and will top off coolant and replace thermostat...hopefully when that is all done the heater will work once again. Any suggestion on anything else to check on for heater not working,?
.

 

The default position of the heater valve is open, it takes vacuum to close it. Is your coolant low enough that you are not getting enough coolant through the heater core?

 

I would NOT rely on that "V:"to bleed the V12, other brands I have seen over the years with that, did not impress.

Drill a 1/8" approx hole in the disc of the stat, and ensure that hole is at 12 o'clock on installation, then the guess work of air getting out is removed.

 

I have them, you DO need the hole, the V gizmo is to allow progressive coolant flow once the thing begins to open - it is nothing to do with air bleed when the stat is closed. Your engine MUST allow air to bleed when the thermostat is shut, that is the reason for the hole, and the hole MUST be at the top 12 o clock position when the stat is installed.