I was going to recommend AMSOIL coolant boost for this, but running your engine for half an hour and needle still being on cold? Sounds like the thermostat is stuck open.
That is, unless the heat was on max with recirculate off. Then, the heater could literally cool the engine down. Not sure if it would keep it that cold though.
That is, unless the heat was on max with recirculate off. Then, the heater could literally cool the engine down. Not sure if it would keep it that cold though.