Losing Coolant from Resevoir overflow

[MiaRover]

My 2001 Discovery II keeps ejecting coolant out of my overflow resevoir thru the overflow discharge hose. There seems to be a great deal of pressure
built up and there is a hissing noise from the top of the coolant resevoir around the spout that the cap is screwed into. I purchased a new resevoir cap but that was no help and there is still the hissing. The overflow hose will discharge coolant at a rate that will deplete my coolant within a normal daily commute, which is about 20 miles.

Has anyone experienced similar problems and what can I do about it.

[John C]

Looks like you have a blown head gasket. Does the coolant smell like gas? Is the oil contaminated with coolant?

[ArmyRover]

x2 on the head gasket make sure to check the oil for coolant. It looks like coffee with creamer if it's contaminated.

If the oil is contaminated stop driving her until you replace the head gaskets or have it towed to a shop for the replacement.

[XtremeMarine]

X3 on the gasket. Sounds like what mine did before the whole engine fried. YOU MUST STOP DRIVING THE TRUCK!