Thermostat test from '97 & '98 Ford manuals:
"Remove the water thermostat and immerse in a boiling antifreeze and water mixture. The water thermostat should begin to open at 86 - 90 º C (187 - 194 º F) 2.0L engine, 84 - 88 º C (183 - 190 º F) 2.5L engine and be fully open at 102 º C (216 º F) 2.0L engine, 99 º C (210 º F) 2.5L engine. Install a new thermostat if it does not operate as specified."
Kinda makes you wonder why Ford would use a thermostat that only starts to open past the optimum you state of 180 F degrees.
Perhaps you should check your facts.
