My 94 Discovery is losing coolant. The coolant is leaking from the reservoir cap. The cap itself is not damaged (I already changed it), but after driving for a 20-30 minutes, the coolant spews out of the cap in a smoky white cloud. The temperature gauge stays normal and there is a bubbling sound coming from the passenger side dashboard. I already replaced the coolant reservoir and cap twice and now am out of ideas. I've been told it could be the heater core or head gasket, but i'm not sure. Any advice?

 

You need to have a shop perform a chemical block test or whatever test they do to verify if your head gasket is leaking exhaust into the coolant, I would bet you have a blown head gasket. By the way coolant bottles, if you are using the newer white one, don't just fail. Sounds like the cap and bottle are being over presurized by the exhaust.