HELP Engine Overheating Coolant Boiling Can't Figure it out
Hi guys, I recently bought a 2007 Mazda 3 with 135000 miles on it from a family friend for a very good deal cause there were some minor issues with it. The original owner said there was a problem with the lights flickering and the AC not working all the time. I drive for work all day for work so it puts a heavy load on the car. The first day I drove it I noticed the flickering lights and it seemed like a relay was wiggin out cause it kept clicking under the glove box and the lights would go on and off during the day while I was driving, with out having the lights switched on. I noticed that the AC worked most the day but after a while it stopped working. Original owner tried to address this and mechanic he took it to said it was the thermosat so they replaced that, along with refilling the AC compressor with fresh coolant. Well towards the end of my day something smelled burning and I looked down and the temperature gauge was all the way to red so I pulled over turned off the car and popped the hood, the coolant was boiling and spewing out the side of the reserve tank, don't know if there is a release valve on this or if it just created its own hole due to the pressure in the system. After letting it sit for a while, I proceeded to drive it home bit by bit with heater on full blast, seemed to help keep the gauge at the middle level, so it wouldn't over heat again and I refilled the coolant. When I got home it was boiling again, I have never seen this. I took it to a trusted shop they took a look at it and said it was the engine coolant fan, which I told them to hold off fixing. They looked at the electric and said they fixed a ground wire from the transmission but after looking at the electrical they said it wasn't the engine cooling fan it was the alternator. I got in touch with original owner and he said the alternator was fixed 3 months ago. So I took the car home cause i didn't fully trust the shops diagnosis. So I pulled the alternator and had it tested at two different auto parts stores and both tests said it was bad. So I put in a new alternator, which helped the electrical light issue but didn't fix them, they still flicker at night on the interior. I drove it yesterday for work and towards the end of the day the engine started to overheat so I let it sit for a while to cool down and when I looked at the coolant level it was almost empty, I had been checking it religiously the past few days since i got it back from the mechanic. So I filled it up and when I got back home it was spewing out the reserve tank again.
Need some help her, I checked the oil cap to see if it was milky and it wasn't, same with the engine oil it was milky either, just to try to rule out a head gasket failure.
Also the coolant doesn't stay green, I checked and it doesn't have oil in it but after a day it is almost brown, is this normal.
I'm thinking it has to do with the radiator and or the water pump. What would make coolant boil, aside from coolant coming out the reservoir there are no leaks in the system and the pressure is there when the engine has been running.
Do you think it could be the water pump not working correctly so coolant is not recycling through the system.
Could it all be connected to an electrial issue?
Some advice would help, thanks