strange, i parked my 1999 expedition on an uneven surface (banked 20 degrees left) and after a while of idling the temperature went up close to H and oil temp hot lamp went on. didn't panic as i know the ford expedition is smart enough to do cylinder deactivation to cool engine in case of cooling system failure. i moved to an even surface and shutoff engine. opened hood, coolant in reservoir was slowly boiling. waited five minutes, restarted and temp was back normal. continued journey with temp in normal range. no power loss, no knocking. my theory is hot coolant in the reservoir touched the cap (because of bank angle) and might have caused cap to expand a bit and let air in or out hence the boilover. coolant levels were normal last i checked, will check again in the morning.