Hongstertruck

High pressure equals low flow, and in this case he lost 1 and 3/4 gallon, that tells me the pressure was so high, I don't think the coolant ever had a chance to circulate at all.
But then again, this is just my thinking. If I'm wrong then I agree with you that the OP will be in trouble.

VTX1800N1

As long as the water pump is working, the coolant will flow through the engine and heater core (assuming enough coolant is in the system to reach the core, which is higher than most of the engine). The thermostat only determines whether coolant flows through the radiator. High pressure in an overheating engine will be virtually the same pressure throughout the engine, so it won't impede flow. In addition, he started the engine from cold- that high pressure overheated condition wasn't there from engine start. The heat had to build up as the engine idled and then drove down the street. At some point, again assuming there was enough coolant in the system to reach the core initially, heat would most definitely be available to the cabin. That might change as soon as he has a major coolant loss.

lhfarm

Here is the report from the Ford dealer:

06F1: COOLING SYSTEM REPAIR
CUSTOMER STATES THERE IS COOLANT LOSS. REQUESTS
PRESSURE TEST/LEAKAGE DIAGNOSIS.
Work preformed by 1380
PRESSURE TESTED TO 15PSI WITH NO LOSS OF PRESSURE
MONITORED PCM COOLING FAN DEMAND FROM COLD TO
244 DEGREES. PCM MAINTAINS HEAD TEMP AT 224 WITH
ONLY 10% DUTY CYCLE. VERY GOOD, HIGH EFFICIENCY.

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Should have I asked for another test? What else should I be watching for? What sort of trouble should I expect?

Barry

Hongstertruck

Barry, just keep an eye on your coolant level diligently. If you're going to notice a significant amount lose then you address your issue with a mechanic. If no coolant lose let's say within the next 2 weeks. I'd think you're out of the wood. GL!

lhfarm

I plan to watch it closely from now on. Again thanks for the help.

Barry