Two days on a phantom coolant leak in a 2008 F-150, turns out it was the heater core bypass hose
I chased a slow drip on a customer's truck for two full afternoons, pressure tested everything and even swapped the water pump out of pure frustration. Finally caught it on a hot engine with the cab heat on full blast, coolant was weeping from a tiny crack where the bypass hose meets the firewall, hidden behind the blower motor housing. Has anyone else had a leak that refused to show up until the system hit operating temp, or am I just the lucky one who wasted 14 hours on a $14 part?
14 hours on a 14 dollar hose sounds about right for a 2008 F-150. Those heater core hoses love to wait until the thermostat opens and the pressure builds before they show their hand. At least you found it instead of throwing a head gasket at it like some guys would.