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[ford_doctor]

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Ford_Doc

Does coolant blowing out of the de-gas bottle usually signal a head gasket issue? It happened to me recently. Also, what does a dealer do to test for head gasket issues?

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To your first question:
Yes, but... if an EGR cooler has a large enough leak it too can cause coolant over flow from the de-gas bottle however symptoms like steam, hydro locking and unexplained coolant loss or more likely to happen first. Coolant overflow is caused by over pressurization of the cooling system. A 16lb cap cant hold the 40+psi of exhaust back pressure that is commonly found in the EGR cooler. Since combustion pressures are much higher than that, head gasket failures are more likely to cause coolant to blow out of the cap.

How do we test for this?
"We" install a pressure tester in line with one of the coolant return hoses and first pressurize the system looking for leaks. If no external leaks are found, the EGR valve is then removed and we inspect for coolant leaking into the intake through the EGR passage. The right exhaust manifold is also inspected for signs of coolant. A minimum of fifteen minutes is recommended for this procedure.

If that test passes, a road test is performed with the gage still installed. Full throttle accelerations and high loads are recommended conditions for this est. A rapid rise in cooling system pressure and or pressures above the system specification indicate a head gasket leak.