Mazda Repair: 1991 Miata coolant leak back of engine, crank angle sensor, coolant leaks

Question
1991 Miata no leaks at idle. When pressure builds coolant leaks through what appears to be vents on the bottom of bellhousing.Could there be freeze plugs on the back of the engine block?

Answer
Yes there is a freeze plug on the rear of the block.  Though not common to fail.  If you have an excessive amount of corrosion in the system them it is possible.  More common though would be one of the heater hoses, a rubber pipe plug (accessible passenger side) below the crank angle sensor.  Other than those the rear cover gasket that the heater hose fits to, and two heat gauge sensors, one head mounted (below the pipe plug) and one mounted to the rear cover though rare.

I would clean the area well, let it dry and use a solvent spray (such as brake cleaner) to remove and oil/coolant residue and degrease the area.  Pressure test the system to 12 psi and watch for the leak to manifest itself.  The rear freeze plug equals major component removal to access.