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So I did a little experiment today. It was a pleasant -27C showing on the dash(-17F). After a short trip I picked up my wife and dropped her off at the grocery store for a bit and said I’d wait in the car because it’s fricking cold. I went and parked the car and at this point the car was just above the blue cold range on the temp gauge. I had the heat on high temp and fan speed 4 and the engine temp dropped to JUST on the upper range of the blue zone after a few minutes. I went to fan speed 5 and it started to dip into the blue just slightly so I went to fan speed 3 and the temp started climbing slowly. Fan speed 2 and it kept climbing. So I turned the fan off completely. I’ve never seen my engine warm up this quick before. I watched it climb all the way to almost half on the gauge within a couple minutes then started playing with fan speeds again but it seems that 0-1 speed the engine will heat up in no time. Anything 4+ speed with a cool engine it does not like being robbed of all that precious heat. Anyways just thought I’d mention how HUGE of a difference putting the heat on 0-1 for a few minutes makes.
Tried this tonight, the engine did heat up faster. But didn't necessarily make the car warmer faster IMO but your mileage may vary. I've defaulted to relying on the heated seats most of and thick gloves during our extra cold week where it is negative fahrenheit temps most of the day.
 

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I believe I have an issue as well now at 35-40F outside temperature as it never gets to operating temperature (my car always starts from ~55F as it's the garage).
I drove today for 30 miles on the highway (15 miles one way, stopped for 4h and 15 miles back); there was a slight hill and temperature went to normal but seconds after passing that hill, it started to drop.

I turned off climate system to see if it would make any difference but when I got home, the temperature was like in the photo (after ~17 miles of driving 90% on highway at 40F).
I've booked it in with the service department to have a look.

I have a feeling the thermostat is stuck open (or almost stuck open).
When I got home and opened the hood, there was no "heat wave" to hit me as it usually did. The coolent level is at MAX.
 

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I believe I have an issue as well now at 35-40F outside temperature as it never gets to operating temperature (my car always starts from ~55F as it's the garage).
I drove today for 30 miles on the highway (15 miles one way, stopped for 4h and 15 miles back); there was a slight hill and temperature went to normal but seconds after passing that hill, it started to drop.

I turned off climate system to see if it would make any difference but when I got home, the temperature was like in the photo (after ~17 miles of driving 90% on highway at 40F).
I've booked it in with the service department to have a look.

I have a feeling the thermostat is stuck open (or almost stuck open).
When I got home and opened the hood, there was no "heat wave" to hit me as it usually did. The coolent level is at MAX.
Good luck, hopefully your service department diagnosis it better than mine did, or I should say they didn't. If I'm not mistaken, if the coolant is at MAX after a drive then that means it's not circulating right and should be warmer right?
 

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Ah yeah. I will tell them to do a check.This is my second Mazda that has a component failure in ~1y of ownership.

I already have a trade-in value for a Tesla Model3 ~4-7weeks delivery and whatever they do tomorrow might make me do the flip and I am also in talks with the same dealer for a MX-5.


~1 month ago at ~39F after ~12-15 mins of driving.
Screen Shot 2021-02-11 at 3.10.12 PM.png
 

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I am booked for this Friday with the dealer.
I have did a test with the scan tool and here's the results:

1. Outside temperature 42F-45F
2. Turned off climate control
2. Started the engine and drove until it reached to 160F on the ODB2 scan app, stopped the engine and checked the upper hoses from the radiator and they were warm
3. I went on a hill up & down twice in sport mode until temperature reached 195F and the needle was right where it needs to be on the dash
4. The moment I came down the hill, temperature started to drop
5. On the way home, the temperature was 170F, I turned on the climate control, got home and let it idle for 5 minutes
6. Turned off the car with the temperature at 165F


At 165F, the needle on the dash look like in the photo. Total distance of my test: 9.3 miles / 25 min.
No errors recorded.
I suspect thermostat valve partially or completely stuck open.

 

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Who doesn't like a graph? :)

I went out again and did some data logging. Bellow you can see coolant temperature on the left, engine load & speed on the right (outside temperature was 47F and total trip was 11miles).
  • 4:33pm -> enter the highway which is uphill and going up to ~70mph and coolant temperature gets to 192F
  • 4:37pm -> exit the highway and quickly drops down to 180F during braking
  • 4:38pm -> back on the highway where I accelerate again and going the other way which is a bit downhill and temperature drops to 165F.
  • 4:42pm -> get off the highway and drive in the city where temperature goes ~175-180F and ends up at ~175F when I get home.
Coolant temp vs speed:
280684


Coolant temp vs engine load moving average:
vs load.png


Graph with engine load (raw data):
coolant2.png
 

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I have this problem too. I first had CEL in November. I've cleared the code 4 or 5 times by now. Its only an issue below freezing. I plan to take the car to the dealer soon.
 

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I've been to the dealer. Before even looking at the car, the service advisor tried to explain how the thermostat works to suggest that it is normal. After insisting to take the car out on the highway for a test, they came back and said that the electronic part of the thermostat is bad; he said that the car doesn't have a classic thermostat but an electronic control module.
The part is on backorder and I'm the third car with this issue. They are going to call me once they get the part and the good news is that I can still drive my car.
It will be fixed under warranty once they get the part.

This is my second Mazda with engine issues in 1st/2nd year of ownership and will be my last Mazda.
 

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Wouldn't those readings make sense if the coolant at the bottom of the reservoir warmed up quicker than at the top, kind of like how the A/C can blow warmer air when you take a sharp turn?
 

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he said that the car doesn't have a classic thermostat but an electronic control module.
.
This is of concern. The new M3 is so loaded with innovative features that the conservative part of me start to think about long term reliability, and service costs. Years down the road, and out of warranty, what would the annual maintenance bill be like? Especially when these "electronic control modules" start failing, and only the dealers can fix them.....
 

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This is of concern. The new M3 is so loaded with innovative features that the conservative part of me start to think about long term reliability, and service costs. Years down the road, and out of warranty, what would the annual maintenance bill be like? Especially when these "electronic control modules" start failing, and only the dealers can fix them.....
You mean compared to, say, a BMW?
 

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Wouldn't those readings make sense if the coolant at the bottom of the reservoir warmed up quicker than at the top, kind of like how the A/C can blow warmer air when you take a sharp turn?
I don't believe it would make sense. My engine doesn't get to normal operating temperature if I do not go uphill or floor it multiple times.
Once it goes to the normal operating temperature (~195F) after let's say doing a 5 mile climb on the highway towards the mountains, all the coolant should have the same temperature as it's circulated in the system. The moment I no longer climb, the temperature goes down to ~170F in the next 15-20 seconds.

As long as I don't go uphill, my car on the highway won't go above 170F even after 50 miles in outdoor temperatures ~45F.
I observed this behavior in the past few weeks. Up until that point I experienced as low as 15F and it was fine.

You can see in the zoomed part how quickly it drops once I exit the highway (which was uphill); I could probably log the altitude which would be more interesting to see.
I could probably repeat the measurements once they change the thermostat (if it doesn't take more than 1/2 months and it doesn't warm up outside).
280755
 

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I don't believe it would make sense. My engine doesn't get to normal operating temperature if I do not go uphill or floor it multiple times.
Once it goes to the normal operating temperature (~195F) after let's say doing a 5 mile climb on the highway towards the mountains, all the coolant should have the same temperature as it's circulated in the system. The moment I no longer climb, the temperature goes down to ~170F in the next 15-20 seconds.

As long as I don't go uphill, my car on the highway won't go above 170F even after 50 miles in outdoor temperatures ~45F.
I observed this behavior in the past few weeks. Up until that point I experienced as low as 15F and it was fine.

You can see in the zoomed part how quickly it drops once I exit the highway (which was uphill); I could probably log the altitude which would be more interesting to see.
I could probably repeat the measurements once they change the thermostat (if it doesn't take more than 1/2 months and it doesn't warm up outside).
View attachment 280755
But you noticed this same behavior on more than one Mazda, right? Or did I misunderstand that earlier.
 

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I have not noticed this on any other car until 3 weeks ago on my car.
I had other issues with my previous Mazda.


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I did not. I am not sure where that confusion came from.


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I did not. I am not sure where that confusion came from.


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Ah ok my bad. Something that was said earlier on and the "until 3 weeks" part thru me. In that case it does sound like a possible issue. But then again if no error readings are going off, then why not just ignore it for now? I mean it's going to be covered if something does fail. And when you get closer to warranty expiration you can decide whether you want to sell or not. It is too bad though if you got a lemon of some sort. Hopefully things turn around for you one way or another.
 

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@iwolffy how did you log your data? I'd like to do the same and see if my dealership will look into it when presented with data. It was roughly 20-30s °F the last time I took it in for this issue and after driving on the highway (total trip was 15 minutes, on the highway for the last 7) to get to the dealership, I could see the needle drop while the engine was running in their drive up indoor service area! I was told this is normal. The manager was there right next to me, saw it happen, the car was blowing out warm air at max setting (not hot), and wouldn't look at it unless there was an error code or if the heater was flat out not working. Manager said I need to use re-circulate more often and not expect it to blow hot air unless I drive on the highway. Idk about others but in every car I had, using re-circulate causes the windows to fog up in the car within a few minutes in the winter. Even with the AC on. That's not a practical solution and this behavior is what I expect from my 20 year old honda accord NOT a brand new vehicle.

Edit: I've got a thousand-ish miles till my factory warranty ends and I have an extended warranty. But I also want a toasty car.
 

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But then again if no error readings are going off, then why not just ignore it for now? I mean it's going to be covered if something does fail. And when you get closer to warranty expiration you can decide whether you want to sell or not.
I do not want to ignore it; not driving with the engine at the normal operating temperature can increase wear and potentially get worse gas mileage.

@iwolffy how did you log your data? I'd like to do the same and see if my dealership will look into it when presented with data. It was roughly 20-30s °F the last time I took it in for this issue and after driving on the highway (total trip was 15 minutes, on the highway for the last 7) to get to the dealership
I've got this interface which was free last week (only needed to pay shipping).
After reading your post and how the dealer was pushing back, I have decided to get the interface, do some measurements and have a way to replicate the issue before going to the dealership.
I've told them that the easiest way to replicate is to take it on the highway and see the needle drop; they did that and I've seen the technician when he came back and went to the service advisor, he told him that he could see the needle drop and the thermostat needs replacing.
I did not had to show them the measurements; having a way to replicate the issue was enough.
 
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