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Cooling System Problems

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#1
Bricks

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Ok, so my car has been overheating lately and I don't know what the cause is. The thermostat has been replaced the radiator has been replaced, the timing belt and water pump all new. What else could be causing the problem and would it be able to be fixed by me with little mechanic knowledge. I think it may be the overflow tank, but would that cause overheating? There is a constant leak and I have to put coolant in there regularly. Can anyone help me? And also is the Dorman overflow tank a good replacement?
Thanks for the help in advance.

#2
Bricks

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2001 Mazda 626 ES V-6

#3
m626er

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are you sure there is no air in the coolant system, if not you may have a craked head or head gasket

#4
Bricks

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I had the cooling system flushed about a month ago so unless air has gotten in it since then. And I don't think there is a crack in the head gasket because there is no coolant in the oil.

#5
Bricks

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Are there any other symptoms of a blown head gasket that I may be missing?

#6
djdevon3

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There are generally 3 things that can happen with a blown head gasket which will cause fluids to disappear.
Oil in the combustion chamber - hard misfires, oil on spark plugs, possible no-start conditions, thick blue smoke from exhaust.
Oil in the coolant (and vice versa) - reduced heat transfer cumulates in overheating, presents itself as milky goop in radiator cap and/or crankcase.
Coolant in the combustion chamber - majority will be burned away unlike oil so the car might continue to run without issue but coolant will mysteriously disappear, thick white smoke from exhaust, random overheating due to coolant loss.

Since we are in winter it might be harder to tell from the exhaust. If you notice your exhaust is unusually thick it might be an indication. Much easier to spot in warmer weather like spring, summer, fall just from looking at exhaust plume.

A blown head gasket can mean a couple of different things. It's not just oil that can dissapear or burn it's coolant too. So if you have to constantly refill your coolant levels and can't find any kind of leak it's possible that you have a blown head gasket and the coolant is being burned in the combustion chamber and shot out the exhaust as vapor.

#7
97Mazda

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"I think it may be the overflow tank, but would that cause overheating? There is a constant leak and I have to put coolant in there regularly."

Did you check it for leaks?...they were a known problem!

#8
djdevon3

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My suggestion on the blown head gasket only applies if you've already checked for and cannot find a leak anywhere. Most common is a leak and 97Mazda is correct. The V6 has an issue with that overflow tank. There might even be a TSB on it.

#9
Bricks

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When the car warms up all of the coolant comes out of the hose from the overflow tank that doesn't connect to anything. I drove it today, no problems I may go check in a lil bit after the car cools down to see if the overflow tank is leaking.

#10
Bricks

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Also, any tips for replacing the overflow tank? Do I need any special tools it looks pretty straightforward.

#11
JeffMerr

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Also, any tips for replacing the overflow tank? Do I need any special tools it looks pretty straightforward.


It's very easy, I just replaced mine yesterday for the 2nd time, seems like every year I have to replace it because of a leak.

All you need is a 10mm socket with extension and a pair of pliers to pull the hose clamps back.

#12
Bricks

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Ok, thanks I will try to do that. But no one ever answered could this leaky overflow tank be the cause of the overheating?

#13
djdevon3

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I don't know anything about the V6 overflow. If it's part of the pressurized system then my guess would be it's a symptom not a cause. Heat and pressure builds, blows a leak in the path of least resistance which should be the radiator cap. If the overflow tank is weaker than the pressure required to blow the cap then that might be a reason why so many people have issues with leaking overflow tanks. Like I said I honestly have no clue but it would explain a lot.

#14
woo7

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Is your overflow tank just getting too full? Or is it actually leaking where it should not be?

One thing I have noticed is that not all thermostats are alike.

Granted, my experience was with a 94, but I believe this should still apply.

The V6 uses what Mazda calls a two-stage thermostat. I don't exactly know what this means other than that your good ol stant thermostat is not the right one.

I went through three thermostats before I decided to get one from the dealer. As soon as I got the thermostat from the dealer I noticed a huge difference. The dealer part looked like the Rolls Royce of thermostats compared to what I had been using.

After I installed the dealer thermostat, no more issues!

I would not be hard pressed at all to believe that the thermostat being stocked by many parts suppliers is not of good enough quality compared to a dealer part.

Just a thought...

#15
djdevon3

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There's no mention of a two stage thermostat in factory manuals. :( It begins opening at a specific temp then gradually goes to full open as temp increases. Need more info on this.





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