me again
Also, the car runs rough. Won't idle at startup. Once warm it idles okay.
Thanks,
George

Sounds like more than 1 thing.
What does it take to over-heat the car?
Starting it in the driveway? idling?...Traffic?
Does it get hot enough to knock or clatter? or are you going by only the gauge?

With engine cold, stone cold, open coolant tank to equalize pressure,
tighten cap again,

now start the engine ,

after 30 seconds open the coolant pressure cap,
if theres any pressure the cylinder head gasket is leaking.

George, a simple test would be to remove the thermo all together, (make sure you seal the connection with silicone or something to prevent leaking while it is out ) see if it still gets hot, if it does youve probly got a failed water pump, which is a simple fix on the 700's,
Some others things you can check is the temp sensor on the head, i remember once the wire on mine had come loose and would ground itself out and cause a high reading, as for the running rough when cold take a look at your Idle Air Valve, if its stuck that would explain the hot/cold running issue.
a previous post on the other thread you made made some good suggestions and asked some questions, answering those questions would greatly help is getting you a diag on the issue. good luck