Phillip,
Excellent timing!!! Just went through this exact thing today. 216, fresh rebuild, drained the coolant to switch from a 160 to a 180 thermostat. Buttoned it up, filled it, started it. It was warming up fine, when BAM, it started puking water violently, out the overflow, AND from under the cap (non-original cap, by-the-way).
Problem was Vapor Lock.
My understanding is that air collects underneath the stat, and prevents the water from circulating. Not sure of the science behind it, BUT . . .
Tried an old mechanic's trick: removed the stat again, DRILLED a
1/8th inch hole in one side of the flange, away from the edge so it's within the circulation pattern. This allows air to escape to the top of the system (upper radiator) even though the thermostat is closed.
Yeah, I guess it defeats the purpose of the thermostat to a VERY small extent, but practically speaking, it doesn't make a difference in warming up. Just ensures the coolant can all circulate when it has to!!!
Won't hurt to give it a try, AND it's a CHEAP FIX!!!
-Michael
