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Discussion Starter · #1 ·
Hello I own a 2007 mazda 3 manual vehicle. Couple of weeks ago I was ag McDonald’s in a drive thru lineup and my temperature was fluctuating all of a sudden. Gave me a p0117 code. My mechanic told me it was most likely thermostat. Had thermostat changed and the system flushed and new coolant put in. It was fine for a week and a half and again yesterday temperature wanted to creep up again waiting in a lineup. Any suggestions what the problem might be?
Thanks
 

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Per the service manual, P0117 had the possible causes:
  • ECT sensor malfunction
  • [Connection] or terminal malfunction
  • Short to ground in wiring harness between ECT sensor terminal A and PCM connector terminal 2AH, 2AK
  • Short each wiring harness ECT signal circuit and ECT ground circuit
  • PCM malfunction
Nothing about all that directs jumping to replacement of the thermostat... Did your mechanic do anything with the engine coolant temperature (ECT) sensor? You can check the connections for obvious damage or corrosion (and even clean the connections with electrical contact cleaner...):
("How to Locate and Replace Coolant Temperature Sensor 2004-2009 Mazda 3 (2.3L)"

Edit: to add, you said "fluctuating all of a sudden". In my experience, erratic or wild swings of a gauge -- especially with something that should be rather fluid or measured like a temperature gauge -- suggest an sensor or gauge issue. It's one thing for a slow climb, or high temp with evidence for actual high temp (e.g., high coolant temp with concurrent high oil temp, full-speed fan), but fluctuating, or erratic spikes seem contrary to the nature of the underlying systems. In my experience, I once had an unpredictably spiking temp gauge; it seemed to resolve with a complicated ritual of burping the radiator, but I eventually traced it to a loose connection at the back of the instrument cluster gauge connections. In another case, I had an erratic and spiking oil pressure gauge; the issue resolved after replacing the pressure sender.
 

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Discussion Starter · #3 ·
The thing is it didn't do an erratic spike. It gradually went up and when it got to hot, it gave me a check engine with that code. My fan never turned on and i have voltage through the fuse. I ordered a new fan with the control module. This all happened when i sas in idle. When i was driving the temp maintained itself.
 

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Discussion Starter · #5 ·
I did say fluctuating but what would of been more proper is "started gradually going up". It didn't shoot up like an arrow.
 

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First thing to do is change the coolant sensor. It isn't' expensive and many times that is the cause.

But, the fan not coming on is a bit strange. If the temperature is going up the fan should come on. Turn on the air conditioning the next time and see if the fan comes on.

Also mildly possible the coolant is so old that it has crud in it and is inhibiting good cooling.
 

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Discussion Starter · #7 ·
The coolant is brand new but i haven't tried to put the ac on. Any ideas what would cause the fan not to turn on?
 
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