Overheating Issue - PLEASE HELP

87jacobsen

Member
:
Mazda 3 2004
Hello All,

I am new to the community, but have searched up and down and have a unique problem with my Mazda 3. Hoping you guys might be able to share your suggestions.

Vehicle is a 2.3L 2004 Mazda 3 HB - I purchased the vehicle recently and since have faced several issues with overheating. Here is what I can tell you:

The Issue:
- At stand still the car cools very well. Temperature gauge reads directly in the middle. I can rev the engine and hold at various RPMs and I do not have any issues at all.
- When the car is driven and at speed (usually about 35mph plus) the temperature guage increases quickly. It does seem to drop a bit at times to an acceptable range, but then returns to hot. Turing heat on in the car helps to cool a bit.

What I can tell you:
- The car has strong heat insdie (the heater core is getting some flow)
- The lower rad hose seems to be cold (which sort of contradicts the above I know), top rad hose is hot
- Coolant overflow is at max level when cold and doesn't seem to fluctuate at all (even when car reaches operating temperature).
- The fans come on at operating temperature

My current diagnostic:
- The fact that the top rad hose is hot and the bottom rad hose is not would lead anyone to think that it could simply be a thermostat getting stuck closed or perhaps just partially opened. The question that I have though, is that if this were the case would the car not overheat in all conditions? (at idle as well as when driven)
- Along the same lines as above, it seems that this may be a coolant flow issue, so I suppose it could be an intermittent water pump? Or, maybe it is supplying enough flow to cool at idle but not enough flow to cool at operating speed / under load?
- Again along the coolant flow issue, it could be any of air in the system, or a clog somewhere in the flow somewhere like the radiator, block, etc.
- Outside of this, I suppose its always possible it could be a head gasket or a crack in the head, or something along those lines which is causing an issue. I just dont see much that would point me there yet, the oil is completely clean, there is no evidence of oil in the overflow tank, no white exhaust, the car runs well, and usually when you see compression pressuring coolant system you would see bubbles forming in the overflow tank, no?

Anyhow, hopefully some wiser folks can point me in the right direction based on the information that I have provided.

Thanks all, and glad to be a part of the community.

87Jaocbsen
 
If your thermostat were not open all the way, coolant flow at idle could be sufficient, whereas driving at road speeds would require greater flow through that smaller opening. The first thing I would do is check the thermostat by dropping it into boiling water to see if it opens all the way.
My MX5's thermostat did something similar, a couple of years ago. Luckily I noticed the ScanGauge readout and temp gauge climbing well above normal as I was driving to the gym.
 
I was having the same issue as you. I don't know if your check engine light is on cause mine wasn't. As the other guy said check the thermostat but as for me my thermostat was fine. I finally got the idea to just change out my temperature sensor and that fixed the problem for me.
 
Might want to get your radiator checked. Sounds like enough flow at idle, but when demand is placed on the radiator for more cooled water it can't oblige.
 
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