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I live in Minnesota so it is a little cold out right now. have a 2013 Mazda3 Touring with 8k miles on it.
since last week the car heats up where the blue temp light goes off and there is decent heat. then after a few more minutes the blue temp light comes back on and the heat will be cool-warm and the light will stay on for around 20 minutes.

never had a 4 cyclinder car before so maybe this is somewhat normal?

got dealer to replace thermostat but that didnt fix problem.
 

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The thing could be that the coolant in the radiator is so cold that when it flows through it cools down the engine temps.

The engine warms up with the coolant in the engine, then once the thermostat opens, cooler coolant flows through the engine. It could be so cold that the coolant that is not in the engine is cold enough to bring the temps back down.
 

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a little under 176 degrees Fahrenheit = Blue light goes off. According to my android device.
 

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Id say its normal especially in Minnesota. My old Corolla would rarely get up to operating temp when it was in the 30s outside and if it did I could watch the gauge plummet when I got on the highway lol

Like others said, your heater is just a small radiator so that could be enough to cool the engine down in really cold weather. You could always try blocking the airflow to the radiator to see if that helps
 

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That seems pretty strange to me, but then again I just looked at Minnesota and some areas are in negative temps so maybe that is normal lol. Twenty minutes is quite a long time, and I'm not exactly sure why the thermostat wouldn't close again once the car sensed the engine temp was actually going down.

I will say here in Ohio where it gets cold (but by no means that cold) and I haven't seen mine do that. I think coldest I have had it out so far is 15-20 degrees though, it just rarely ever gets that cold here.
 

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Even with the thermostat closed there could be enough cold air swirling around the engine compartment to cool it down. Especially since these motors are all aluminum theyre great at shedding heat
 

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That seems pretty strange to me, but then again I just looked at Minnesota and some areas are in negative temps so maybe that is normal lol. Twenty minutes is quite a long time, and I'm not exactly sure why the thermostat wouldn't close again once the car sensed the engine temp was actually going down.

I will say here in Ohio where it gets cold (but by no means that cold) and I haven't seen mine do that. I think coldest I have had it out so far is 15-20 degrees though, it just rarely ever gets that cold here.
The thermostat will close again, but all that cold coolant already made it past and the engine has to warm it up again.

my car did it this morning and it was 8* outside
 

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The thermostat will close again, but all that cold coolant already made it past and the engine has to warm it up again.

my car did it this morning and it was 8* outside
Yeah I get what you're saying, I just am surprised it takes a solid 20 minutes to make the light go off (which isn't even full operating temperature) just because you now have some more coolant in the system (requiring extra energy to warm up, and having mixed with the warm coolant which has now been cooled down.)

I guess with running heat at the same time for the cabin that does help explain it more.

I am no thermodynamics expert per say, but I am certainly one in training and will actually be starting my first real job working in a similar field. So this topic interests me quite a bit :cheesy:

I find it a little annoying that this happens honestly, if you had a way to slowly let the coolant in the already warm coolant flow the engine temp wouldn't necessarily have to suddenly drop so low the the light comes back on. Perhaps this is something for me to learn and eventually design a system that behaves a bit differently at very cold temperatures :thumbup 1:
 

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Yeah I get what you're saying, I just am surprised it takes a solid 20 minutes to make the light go off (which isn't even full operating temperature) just because you now have some more coolant in the system (requiring extra energy to warm up, and having mixed with the warm coolant which has now been cooled down.)

I guess with running heat at the same time for the cabin that does help explain it more.

I am no thermodynamics expert per say, but I am certainly one in training and will actually be starting my first real job working in a similar field. So this topic interests me quite a bit :cheesy:

I find it a little annoying that this happens honestly, if you had a way to slowly let the coolant in the already warm coolant flow the engine temp wouldn't necessarily have to suddenly drop so low the the light comes back on. Perhaps this is something for me to learn and eventually design a system that behaves a bit differently at very cold temperatures :thumbup 1:
One way you can counter it is let your car warm up in the morning before you start driving. just let it warm up until the blue light goes away
 

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It's 9 degrees air temp here in Chicago. Started my stone cold car and watched how long it took the temp light to go out. I drove the car after about 30 seconds of warm up. I drove city speeds in stop and go traffic and it took just about 3 to 4 minutes for the light to go out. I didn't have the heater turned on during that time. I then blasted the heat for the rest of the drive home. I saw air temps drop to 7 degrees and then back up to 8 degrees while driving. The blue temp light never came back on in the 30 minutes it takes me to drive home from work. I will say my car has a very weak heater compared to other 4 cylinder cars I've owned. I'd put a scanner on your car and watch the actual temps your running.
 

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The blue light on mine kicks off at 128 deg
179-180 is normal temp but have seen 205-208 deg in the summer in traffic. ( no red light )

I have part of my grill blocked, well most of it. As long as it under 60-65 and not a lot of stop and go it stay around 175ish. But even with it blocked and no heat on I have seen it drop to 155-160 just by coasting down a hill. That is with temps in the teens.

I used coroplast, think plastic cardboard,zip tied in.
It shortened the distance till the blue light kicks off by almost a mile.
At about 20 degree without it took 7.5-10 miles to reach 170, now 3-5 miles.
 
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