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Old 12-01-2011, 07:00 PM
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Join Date: Dec 2011
Posts: 2
Default PO126 05 mazda3

PO126 - insufficient coolant temp

My 05 Mazda 3 is at 111000 miles bought used 3 years ago at 60000 and this the first issue I have had with it since before I bought it when they replaced a tranny mount. I've noticed all today that my car has been taking longer to heat up and the check engine light came on after driving a little over 100 miles. My fluid was at the "min" lvl and filled it up and issue still persists. I am not sure what the next step would be since there a few issues it could be. What would be the best next step? I was thinking of flushing my coolant system and replacing thermostat since the few forums I've read here have the thermostat going out at at 36000-101000 in the 2007-08 not sure what if any issues it had before I got it. Any help would be greatly appreciated.
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Old 12-03-2011, 10:21 AM
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Join Date: May 2006
Posts: 1,447

Yup it's the thermostat. The OEM one has a tendency to stick open. Since it can't close the coolant continues to cool when the car doesn't need it to and you say hello to Mr. CEL.

I actually just replaced my thermostat for the same problem a couple of days ago and it fixed the problem immediately (well after I reset the code). It came on at the very end of a 5-7 hour highway drive, but even after that the car ran fine and didn't appear to have an issue heating up. After replacing it the car clearly heats up more quickly.

If you have some standard DIY skills you can replace it. Getting to it's a little tight but is much easier from the top of the engine (plus then antifreeze doesn't spill on you). I recommend removing the tensionor pulley assembly from the engine block as the thermostat is right underneath it. You'll need:
-14mm socket
-12mm socket
-10mm socket
-8mm socket
-breaker bar
-socket wrench
-various socket extensions (it's tight getting the bolts holding the thermostat on)
-large pliers (for compressing hose clamps)
-container for coolant (plus funnel, etc.)
-ramps or stands/jack
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Old 12-03-2011, 10:23 AM
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Join Date: May 2006
Posts: 1,447

Oh and I forgot to add DON'T buy an aftermarket thermostat at an auto parts store. The consensus around the forums is they're all subpar and will require replacement again soon. The OEM thermostat (apparently an improved part) can be had for about $50 shipped from Online Mazda Parts
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Old 12-03-2011, 05:17 PM
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Join Date: Dec 2011
Posts: 2

Thanks, the help is very much appreciated.
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2006, bad, check, code, drive, ect, engine, installing, light, mazda, mazda3, mpg, po126, safe, thermostat

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