Thread: Zips riser

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Don,
I'm assuming that you had the pressure cap in place for this test, right? What is the pressure rating of the cap? Regardless your answer, 205F is not hot enough to boil pure water with a 212F boiling point (you're very near sea level), and with a 50/50 mix your boiling point is up around 265F at atmospheric pressure. With elevated pressure (the cap) that boiling point increases. If you're seeing water blowing out of your coolant overflow tube at anything below a coolant temperature of 275F to 290F you have a pressure problem. I suspect you've got a blown head gasket. If not, then it may be worse, because somehow cylinder pressure is getting into your coolant passages, causing your radiator to over-pressure at near normal operating temperatures. Maybe you can do a cylinder leakdown test to see if one or two adjacent holes are losing pressure, and watch for bubbles in your radiator while doing the test.