My 1991 mazda mx-6 resevoir coolant tank boils and spills out .

check ur switching box make sure is turning the ac off disconnect form the switching box inside and see if ac goes off if so control box is at fault repair or replace. Good Luck

Sounds like you need a thermostat. Check your anti freeze level.

If no heat from heater its likely low on coolant, and antifreeze in cab on the floor means its probably leaking from the heater core.

YOUR ENGINE TEMPERATURE SENDING UNIT NOT WORKING.ANY TIME COOLANT BOILS OUT OVER FLOW JUG.YOUR ENGINE IS OVER HEATING.REPLACE RADIATOR PRESSURE CAP AND THERMOSTAT.THERMOSTAT LOCATED IN CYLINDER HEAD FOLLOW RADIATOR HOSE IT WILL TAKE YOU RIGHT TO THERMOSTAT.THE THERMOSTAT IS IN THE HOUSING.

Check the air intake tube that goes to the throttle body, Check for cracks or leaks, This can cause unmetered air to get by the mass air flow sensor

I had the same problem with my 199 cougar 2.0 4 cyl.
The problem was air in the cooling system.

I had to bleed the air out of the system, and now the heat
works much better.

I put a flushing tee between the back of the thermostat and
the heater core, and made sure that water flowed out of there.
Then I disconnected the small hose from the top of the coolant
resevoir, and poured water into it using a funnel until the coolant
level started to rise in the coolant resevoir. Then started the car, left the radiator cap off, and let it come up to temperature (thermostat open)
then over a period of about 5 minutes, periodically "goosed" the engine to clear any remaining air bubbles.

The heat is MUCH better now.

If car heats up quickly and overheats , the problem is the thermostat. The thermostat stays closed and traps coolant in the engine untill it reaches about 185 degrees , than the thermostat opens and allows coolant to flow to the radiator where it is cooled by airflow. ( airflow while driving is usually sufficient ) while idling , or in slow trafic , the fan keeps air moving through the rad. The heater core is strictly for heat in the winter inside the car. The thermostat is the most likely cause of the problem , and even if it was good before , the overheat / boil situation likely cooked it anyways. I am assuming the water pump is still getting turned by a belt. No water circulation by pump would cause same symptom as bad thermostat. Overflow and expansion bottles are designed several different ways on different cars , but the theory is that as the engine heats up and the coolant expands , it goes to the tank. Later , as engine cools down after being shut off , coolant contracts. Radiator is replenished by coolant returning from expansion bottle.

Hi!
It appears we have an Air lock scenario and you will need to perform a system Bleed.
Park the vehicle on level ground, when cold remove coolant filler cap, start engine and leave to idle, turn heater on full and blower to max. When engine reaches operating temperature watch and listen near coolant filler, keep clear as gurgling and hopefully a boil over should occur. Top up with very warm coolant and wait as it may do it again.
Check for heat inside vehicle if warm replace coolant cap but keep an eye on temperature gauge as the ~Air lock may have moved on from heater matrix/core so proceedure needs to be carried out again from COLD.
If persistent boil ups/over attention must made in the cylinder head
or gasket area, or possibly water pump?
Please press the Blue button to appraise my FREE Efforts, Thank You!
Paul 'W' U.K.

Hi!
Looking at your description I feel a Air lock scenario?
Have you tried a system bleed?
Park vehicle on level ground, when cold remove coolant filler cap, start engine leave to idle, turn heater to max and blower full. Wait for engine to reach operating temp, keep clear of coolant filler, listen as hopefully gurgling then a boil over will occur, top up with very warm coolant wait as it may boil over again.
Check for heat inside vehicle, if hot replace cap but keep eye on temp as air lock may have just moved out of heater matrix/core so boil up may happen again.
If the bottom hose continues to constrict and heat inside car then possible head gasket issues.
Good luck! hope I sorted it for you? if so press the Blue button please! for my FREE effort's I Thank You!
Paul 'W' U.K.

From Haynes Repair Manual #36071, Ford Ranger Pickups 1993 - 2005 and Mazda Pickups 1994-2005 B2300, B2500, B3000, B4000: (1)Disarm the airbag system; (2)allow the cooling system to completely cool down; (3)using a thick cloth for protection, turn the radiator filler cap to the first stop; (4)step back and let the pressure release; (5)once the pressure has been released, completely drain the cooling system; (6) working within the engine compartment, loosen the ****,ps on the heater hoses at the engine compartment side of the firewall, twist the hoses and carefully sepseparate them from the heater core tubes; (7)plug or cap the heater core tubes to prevent coolant from spilling into the passenger compartment when the heater core is removed; (8)place a plastic sheet on the floor of the vehicle to prevent stains if the coolant spills; (9)remove the instrument panel; (10)remove the PCM heat sink and ground strap; (11)remove the heater plenum chamber; (12)separate the heater core from the heater plenum chamber; (13)installation is the reverse of the removal with the following additions; (a)fill the cooling system; (b)run the engine, check for leaks and test the heater