HELP Engine Overheating Coolant Boiling Can't Figure it out - : The site for all your Ford Mazda and Volvo needs
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post #1 of 3 (permalink) Old 09-12-2018, 10:32 AM Thread Starter
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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
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post #2 of 3 (permalink) Old 09-12-2018, 11:54 AM
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Well, here is my two cents (and that's about all my advice on this topic may be worth).

I think the brown coolant is a huge clue. You may have hit the nail on the head with the radiator and/or water pump. I don't think the coolant has circulated on a regular basis causing the overheating. And the fact that it went stagnant (and may have been refilled a lot with just water by the original owner????) probably caused some rust issues.

It could be time to replace both the water pump and the radiator and get the cooling system properly flushed (with chemical cleaners). Or perhaps just replace the water pump first and get a flush done. I'm not sure if pulling the water pump to check it, but not replace it, is worth the hassle. Maybe. An OEM water pump is about $100.

The electrical issue, like with the lights flickering, worries me.
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post #3 of 3 (permalink) Old 09-12-2018, 03:45 PM
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BLUNT! You purchased a car for commuting..with known issues.... not the best idea?
IMHO please DONT take offense, but your are over your capabilities to diagnosis and resolve all the issues and there are a few and the battery is one that has been over looked.
My STRONG suggestion is to locate a service shop in your area that advertises employing ASE Technicians and have them do a basic diagnostic check and evaluation. This is an hour procedure that will run you about 75-100 bucks. These ASE service shops will find exactly the issues and give you choices on correcting them.

What I am very surprised is that you either did not mention or it was never checked by anyone is the DTC log and the monitors. I find it suspect that the check engine light never appeared?

This is all I can tell ya.....
Good Luck!

Last edited by M3RacerX; 09-12-2018 at 03:48 PM.
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