[2011]

Hey guys, new to the forum as its my first Mazda. 2011 Mazda 3 GX Sedan 2.0 L4

Currently have no heat at idle, only when Rpm's are above idle.

Just changed thermostat & coolant level is good; did the burping procedure for air removal. (2500 rpm cap off car jacked up) Also flushed the heater core, had clean water coming out. Still have the inlet hose much hotter than the outlet though.

Other thoughts on the problem:

Water pump bearing/impeller shot? Pulley doesn't seem to have wobble to it and is not noisy
Serpentine belt tension etc
Blend door or heater control valve ( I don't know much on these 2)
Degas/coolant fill bottle clogged/ or cap no good
System doesn't seem to build pressure even when hot
Air locked ? There is no bleed screw/rad cap or temp gauge makes it difficult

Any ideas appreciated, don't want to throw parts at it ! haha
Thanks

 

[GerryB]

Do you have a temp gauge? If so, how is the temp while driving? I'm leaning toward a lingering bubble in the system.

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[2011]

No temp gauge, just the blue light before engine reaches operating temp

 

[GerryB]

Ah, the damned blue light lol. Try burping it again. Sometimes there's a stubborn bubble.

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[M3Nitro]

You did not mention what were the problems that lead to making the service you did?

Name of thermostats used. This will tell me if it had a giggle valve?

Without accurate measuring of temperature by using a hand held tool like a Raytek MiniTemp it hard to accurately determine operating temperatures. I would also be inclined to do a OBDII direct access diagnostic check to see if there are any engine codes, even if you are not showing a light. If you have that kind of device you will be able to check other temperature areas that the sensors are sending information the the ECU.
The the air mix links and air mix actuator, may need to be inspected.

The "blue light" is set to go off @129.9F

 

[2011]

Ran OBD2 check no codes
The thermostat I installed is a Gates 34046 and has a jiggle pin

I believe it has a jiggle pin that only can be installed one way as the thermostat is attached to the housing