Originally Posted by Nemmisis1
It's your tstat... Sounds like it get stuck and when your engine ges hot it builds pressure (higher) and blows open the stuck thermostat.. Replace it or open it up to inspect it.. Maybe corroded if dirty flush your whole system out
Originally Posted by eight-bit
They leak, let air into the system, causes gurgling noise. The noise seems to come from right against the firewall, slightly to the passenger side, right?
Notice your windshield fogged up from the inside in the mornings?
Massive fluctuations on the temp gauge are caused by the air in the system from the leaking heater core.
Source: went through the exact same thing with my '00 Dakota.
Both of these!!!! I'd do both being as you have to dump all your coolant to do the heater core anyway.