Automobile(s): 2002.5 F55 STS/64500mi, 2004 Ford F150 SuperCab4x4
MD Eastern Shore - Kent Island
Re: Blown HG?
Depending on what car year, model, and RPO you own, you might have a leaking engine oil cooler or transmission fluid cooler. That is a more common failure which puts oil in coolant or vice versa. The head gasket problem generally causes coolant loss due to overpressure in the system caused by exhaust gas blowing into the coolant.
The exhaust gas test measures gasses in the airspace over the coolant in the surge tank, not the coolant itself.