[Blue Bowtie]

There may be an air bubble in the system. This would account for the lack of heat from the HVAC system and the wild fluctuation of the gauge. It would also explain the sludge creation in a DexCool system.

If there is a leak from the pump or the gasket, the pump would need to be removed to repair the leak. It would make sense to install a new or reman pump at that time just to avoid the possibilities of a shaft seal leak, slipping pump impeller, or failing bearing. The replacement pump cost is negligible.