I was able to get some help, and dropped the Jeep off around 10:00 AM. I called Jeep Masters at 2:00 PM, and they had already completed a very comprehensive diagnosis to determine the engine condition, specifically looking for a blown head gasket or cracked head. They described several tests I was aware of, and a couple I had not heard of before. Hearing the descriptions, I was convinced they had done what they were telling me. They did determine the overheating was caused by the radiator cap not holding pressure, as I had suspected. They found a bad throttle position sensor that was setting the check engine light; the hot coolant had gotten into the wiring and shorted out the sensor. They also found a couple of other, non-related items that I optioned to go ahead and take care of, since they had access at the time (bad ignition cables and rotor, and throttle body contamination buildup).\r
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