On the drive home I got stuck in a busy intersection that took several lights to get through. It got up to 240 before i cranked up heater to help draw down heat then I pulled over and let it cool before I finished the drive.

Checking exhaust gas in the coolant sounds like a good next step. There is a warranty on the replacement engine, but it has some time restrictions on it that I'll have to review. Basic compression check on all cylinders looked good, but I did not do a leak-down test.