I was about to say that the water pump is already busted but you said you already replaced it. You also removed the thermostat so there shouldn't be any obstruction of water.

Someone here might have a better idea on what to look next, so let's wait.

 

Thanks for your reply. I am thinking perhaps there may be an air pocket somewhere in the engine?

 

If you haven't tried, perhaps you can try to remove it. Remove the radiator cap then start the engine. Let it run for about 3-5 minutes until you see the water in the radiator "bubble up".

That is the indication that you are releasing air. Water level should go down. You now add water until the level stabilize.

Once you are definitely sure that you have removed all air pockets, the thermostat is running perfectly, and assuming that the water pump is working, then you can now replace the water with a radiator coolant and do the procedure for removing (again) the air pockets.

 

That's my thought. It needs to be burped.

Sent from my SM-G960U using Tapatalk

 

Thanks for your reply

 

Hello. If you did a heater core bypass it will never blow hot because you bypassed hot coolant away from it.
If there is not enough water the pump has nothing to circulate. This happened to my v6 as well.
My solution was to disconnect the hose from the overflow and use that to fill coolant. I would pour it down the hose towards the radiator and vigorously squeeze every coolant hose I hould get my hands on. The best were the upper and lower hoses. Squeeze them hard and fast...?

 

With the shot gun approach to trouble shooting the original problem will never be known. That said, with all those parts replaced, the only logical thing left is air in the system.
I looked up removing air in Ford V6 engine cooling system since this Ford V6 . Article said to fill system and leave cap "off" so air can escape while running the engine. After a bit the level should drop, top off the cooling system again. Drive the car with cap on and monitor the temp gauge. Recheck coolant system after engine cools off.
Before starting, know the cooling system total quantity, then add back that quantity. A bit less then capacity will go back in because not all may not drain out from the V shaped engine block. That way you know where you stand filling it back up.
If not servicing with 50/50, be sure to use distilled water with the straight coolant and not tap water in your aluminum engine!

 

... be sure to use distilled water with the straight coolant and not tap water in your aluminum engine!

I forgot to mention this, the use of distilled water. If I may ask, am I doing any harm if I were to use tap water just to flush the radiator? I did this to my old vehicle by running it at idle with the drain plug removed until the water is clear.

Afterwards, I stopped the engine and let it drain. That is the time I filled it up with a ready mixed coolant.

 

Some things I've found that help air get out of a cooling system in general - not specific to Mazda.
1. Make sure there is a tiny bypass hole in the thermostat. It there isn't then drill one. Make sure you use an OEM thermostat. I've used many aftermarket thermostats for older cars where there is no other option. In these cases the bypass hole would be missing. The bypass hole allows air to pass by the thermostat and a tiny amount of coolant to flow. This helps bleed the system. I don't know if Mazda OEM thermostats have bypass holes.
2. Squeeze the upper radiator hose by hand to try and get coolant and air to move. I've done this many times and can get most of the air to bleed out of the radiator part of the system.
3. Use a point and shoot IR thermometer to read temps around the engine. If anything gets too hot like over 100C then turn the engine off. Seeing what's hot and not is important to know what's circulating and what's not.

 

Be advised that if the coolant level is too low the temperature gauge wont read anything. The cylinder heads will be running dry and the temp gauge will say cool. The first sign things are about to go very bad is the smell and then very quickly the valves will start making a terrible racket as the vehicle starts detonating. At this point it usually a matter of seconds before all is lost.
See #2 above.

 

This is why I don't suggest doing drain and fills on your cooling system. Looks like you clogged something.

 

Not keeping fluids clean and fresh is precisely how things get "clogged". Coolant is a lubricant, heat conductor, viscosity modulator, and anti-freeze and important for keeping the moving parts operating freely as well as preventing corossion between different metal types. An impeller (water pump) is designed to move liquid and will not function in air. Any air pocket in the cooling system will result in lack of circulation and as a result overheating.
Change it out every 3-years