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So, got my car today with the new thermostat. Sadly I wasn't able to get info regarding the old one. Now the car is heated up in 3kms, roughly.
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2019 Mazda3 AWD AT
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Nice! so it's only me with the thermostat changed twice that doesn't warm up properly.
 

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2020 CX-5 GT 2.5L 2011 3i 2.0L
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I have got the "B" revision one.
Good to read that the new part resolved the problem with your vehicle.

According to the latest version of the TSB, the new part number is supposed to be PYFD-15-16ZA. You wrote 'B' version, so does that mean there was a different part number than that one listed on the paperwork they gave you?
 

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Good to read that the new part resolved the problem with your vehicle.

According to the latest version of the TSB, the new part number is supposed to be PYFD-15-16ZA. You wrote 'B' version, so does that mean there was a different part number than that one listed on the paperwork they gave you?
In the European TSB is version "B" used for MT. I do not have AT. I have got "A" from the factory and this got replaced in 2020 by "B" in the production.
 

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Ah yes, MT. Thanks for that info.
 

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I've booked another service visit this year for an oil change and I'll report again the coolant issue and see what it would do as it's fairly unlikely to get two new bad thermostats (even if old part).
Now it's ~35-40F and I would need more then 25 miles to get to normal operating temperature so would be "easy" to troubleshoot and validate the fix.

Hopefully next year the chip shortage will get better and I would be able to get rid of Mazda (just before my 3y warranty expires).
 

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Something else worth mentioning that I noticed today: after 10 miles, having the climate on Hi, that’s the best it ca do: barely any heat (fan speed stays on 2nd bar).

I then pushed the car harder to get the temperature up, idle and manually put the climate control on Hi with fan on max speed and this is a timelapse of the gauge (this is at 42F):
Idling more than 2-3 minutes (long traffic light or catching the same light twice) would barely provide any heat; it's been now 1 year since I'm facing with this problem, changed thermostat twice under warranty and with the current market, flipping the car for something else would cost more than I want to spend.

Does anyone have experience with lemon law? I'm trying to see if this qualifies for it.
 

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I've seen on a YouTube video from Europe how temperature decreases on the gauge during engine brake after pushing the car at 220km/h on a 2021 model with SkyActiv-X engine.
Either that car has a faulty coolant control valve or I'm just super picky with mine, monitoring and reacting to these changes (as none of my previous cars had that needle move)
(watch from 3:30 to 4:00)
 

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... or I'm just super picky with mine...
Based your post just before this one, I don't think you're being picky at all, because IMO there is definitely something wrong with your vehicle's cooling system. One thing I don't understand is why the ECU is not setting a P0126 code, as a result of the temps in your video. In any case, I can't imagine Mazda telling you there's no problem when they see those temps on your next visit to them. But if they replace the coolant valve with the new part number, and it's still having this same issue, then I guess the only solution at that point would be for you to drive it off a cliff:rolleyes:
 
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Based your post just before this one, I don't think you're being picky at all, because IMO there is definitely something wrong with your vehicle's cooling system.
I did the same test on the 3-Series and the result is the same: at 35F, idling with max heat on for 3-4 minutes will cause temperature to drop. (video)
I had to wait for 35-40 minutes in a queue for a drive-in covid test, moving very slow and mostly indling and had time to experiment in Mazda3: with climate control at 70F, turning off A/C compressor will bring the needle where it's supposed to be and stay there; turning the A/C compressor on, will cause temperature to drop.

I think that's... normal? because A/C compressor will also start the fan and take heat out of the radiator.
 

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I did the same test on the 3-Series and the result is the same: at 35F, idling with max heat on for 3-4 minutes will cause temperature to drop. (video)
I had to wait for 35-40 minutes in a queue for a drive-in covid test, moving very slow and mostly indling and had time to experiment in Mazda3: with climate control at 70F, turning off A/C compressor will bring the needle where it's supposed to be and stay there; turning the A/C compressor on, will cause temperature to drop.

I think that's... normal? because A/C compressor will also start the fan and take heat out of the radiator.
There should be no coolant moving from thermostat housing to the upper hose of the radiator until circa 80 degrees celsius. Btw guys, My M3 got the problem back only after few days of the "new" thermostat installed. It is supposed to be that updated one. Dealer told me that they will try to "reinstall" the software. I doubt it will work. My car has 2.0 G European market. MT.
 

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Damn. First time when Mazda replaced my coolant control valve (as they don't like to call it thermostat), they also called me one week later for a "software install" as that's what Mazda have told them but the same issue after that.
I'm wondering what is going on there and if the problem is actually solved immediately after the coolant control valve is replaced (so per the dealer tests, it's fixed) but comes back soon after.

I've kept saying to my dealer that they didn't do proper testing after changing the coolant control valve but maybe they did if there is something causing the issue to come back after a matter of days.

Having two coolant control valves changed, I don't believe the issue is there for my car at least.
 

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.... My M3 got the problem back only after few days of the "new" thermostat installed. ...
That amount of time and drive cycles sounds a bit to me like adaptive values that were modified by the ECM, which then resulted in the valve being incorrectly controlled. I'm not sure why they would even want the cooling system to have adaptive capability, but perhaps it has something to do with trying to improve the warm-up cycle (which I guess would be a good thing if done correctly).

You might be able to prove this theory by disconnecting the battery overnight, in order to reset all of the adaptive values back to the original settings from the factory. After doing that, if you subsequently see the same 'good' behavior from the cooling system again for another short period of time, IMO that would go a long way to proving that some 'learning' by the ECM is causing this issue. And if that did happen, and you could repeat the same sequence of events every time, that would completely confirm 'learning' as being the culprit.
 
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So, news today. I have been to Dealer to ge the ECU "restarted" as the disconnection of the battery will not make any difference (Maybe Hybrid battery keeps it alive, dunno). It has reseted the adaptation values and on the way back it went from cold to the OT in 4-5 minutes. I will keep eyes on it. It seems the problem is the ECU and it's adaptation values it saves over time.
 

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So, news today. I have been to Dealer to ge the ECU "restarted" as the disconnection of the battery will not make any difference (Maybe Hybrid battery keeps it alive, dunno). It has reseted the adaptation values and on the way back it went from cold to the OT in 4-5 minutes. I will keep eyes on it. It seems the problem is the ECU and it's adaptation values it saves over time.
Sounds like @edmaz might have nailed it. I don’t think adaptives are hybrid battery related as my previous Kia had to have them reset by the dealer too. Of course now the risk is that the maladaptive behavior is relearned and comes back, unless Mazda provides a more permanent software update to the faulty logic. Will be interesting to see if “resetting adaptives” fixes for everyone.
 

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So, news today. I have been to Dealer to ge the ECU "restarted" as the disconnection of the battery will not make any difference (Maybe Hybrid battery keeps it alive, dunno). It has reseted the adaptation values and on the way back it went from cold to the OT in 4-5 minutes. I will keep eyes on it. It seems the problem is the ECU and it's adaptation values it saves over time.
Quite an interesting and potentially very helpful result there, and thanks for sharing it! Unfortunately, if your vehicle's issue really is being caused by adaptive learning by the computer, then a software update from Mazda will be required to fix it.

Is your dealer on board with what we're discussing here? You would need them to communicate with Mazda Corporate, so that they can get to work on the required change that will fix this problem. If not, do you know if there's a way to contact Mazda Corporate directly yourself in your country? Here in North America, we can open a case with Mazda and communicate with Corporate directly ourselves. If your dealer isn't going to carry the ball for you on this, you might need to find out how to contact Mazda directly yourself.

And of course now we're also wondering if this adaptive learning thing might also apply to our vehicles, particularly the non-hybrid models. In any case, I hope Mazda will be able to get this resolved for you, and the sooner the better because vehicles should not have the engine running colder than it was designed to, for any significant length of time.
 
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My Mazda is at the dealer for the past 2 days with my list of issues, including (again) the engine temperature.
I don't know details but I've seen on MyMazda that my tire pressures reset and that they put 4 miles on it so hopefully they are doing some testing there.

Btw, not sure how related it is but for me, the issue seems to have happened (or I've started noticing) since I moved and Mazda sits in garage at 55-60F (12-15C) even if outside is 25-40F; I start the car in the garage at 50-60F and seconds later the car is put in a different temperature range; if there's such a thing as ECU adaptation taking place, it could be that this change in temperature that my car gets at start-up might confuse the algorithm (unless was accounted for).
The engine bay is probably even warmer than my garage during daily-drives as this is the garage temperature when I bring the car in (garage heats up from the heat while engine cools down).
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If the ECU is the one that is commanding these values, it would make sense than why no fault code.
 

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Quite an interesting and potentially very helpful result there, and thanks for sharing it! Unfortunately, if your vehicle's issue really is being caused by adaptive learning by the computer, then a software update from Mazda will be required to fix it.

Is your dealer on board with what we're discussing here? You would need them to communicate with Mazda Corporate, so that they can get to work on the required change that will fix this problem. If not, do you know if there's a way to contact Mazda Corporate directly yourself in your country? Here in North America, we can open a case with Mazda and communicate with Corporate directly ourselves. If your dealer isn't going to carry the ball for you on this, you might need to find out how to contact Mazda directly yourself.

And of course now we're also wondering if this adaptive learning thing might also apply to our vehicles, particularly the non-hybrid models. In any case, I hope Mazda will be able to get this resolved for you, and the sooner the better because vehicles should not have the engine running colder than it was designed to, for any significant length of time.
My dealer is very helpful and there is no problem contacting Mazda Czechia directly. If this ECU "reset" will not help, another step is contacting Mazda directly and wait for an response. I see the problem in the TSB itself. There is no mention about a "reset" of the ECU, so dealer will not do it. I have driven a few separate journeys today and everything seems to be working again, so it must be software related.
 

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... Btw, not sure how related it is but for me, the issue seems to have happened (or I've started noticing) since I moved and Mazda sits in garage at 55-60F (12-15C) even if outside is 25-40F; I start the car in the garage at 50-60F and seconds later the car is put in a different temperature range; if there's such a thing as ECU adaptation taking place, it could be that this change in temperature that my car gets at start-up might confuse the algorithm (unless was accounted for).
...
Now that's a really interesting piece of information! Yes, it's easy to imagine someone making a design mistake by taking the first ambient temp value and not understanding the need to possibly subsequently adjust it. If the stealershp doesn't come up with a resolution for the coolant system issue, you could probably determine if that's the case by leaving your vehicle outside the garage for a day or two. A bit annoying for you, but a big plus if doing so actually confirms what we're speculating here.

Now having said all of that, I seem to recall you posting that your vehicle failed to warm up properly on your way home from Mazda, immediately after they did the last coolant valve swap. If that's correct, it would tend to eliminate the adaptive learning theory being the root cause, at least in that particular instance anyway.
 
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