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I'd be also curious to see how many actually have this problem and are not aware.
I started a thread on reddit earlier this year and most of the replies were that if I don't have a check light on, I shouldn't worry and that I should treat it as I would have no temperature gauge (my previous Mazda car didn't had one).
 

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2020 CX-5 GT 2.5L 2011 3i 2.0L
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I'd be also curious to see how many actually have this problem and are not aware.
I started a thread on reddit earlier this year and most of the replies were that if I don't have a check light on, I shouldn't worry and that I should treat it as I would have no temperature gauge (my previous Mazda car didn't had one).
Yes, the majority of owners don't pay attention to stuff like this, so there could be quite a few vehicles with this problem now, or will have it sometime in the future.

Taking into consideration this new information that you found from the Russian, here's a question for you. Based on what he wrote (and the pictures), we're now thinking that the coolant valve seals can potentially be damaged by higher coolant temps. And you have confirmed via testing that 3 of these valves in a row have not performed correctly on your vehicle. So the new information suggests that maybe all 3 of those valves experienced damaged seals, instead of having that 'hollow area' manufacturing defect described in the TSB from Mazda.

However, your driving pattern that you mentioned earlier sounds like the vehicle rarely (or never) sees coolant temps get over 200F. Is that correct, or is there perhaps something that you didn't mention, such as some fairly long period of idling of the vehicle while parked, or very long steep uphill climbs after being warmed up?

It takes a number of minutes of idling in place (or a long steep climb) for the temp to get over 200F, depending on ambient temp. So things like waiting at traffic lights won't be long enough to send the temp up that high. And the coolant should always stay under 200F while the vehicle is moving, even on very hot days. So can you think of anything else which might have caused the coolant temps to get up into that higher temp zone?
 

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I believe if those seals break, it will break in time; when I got my thermostat replaced, the problem was not fixed the moment I took it out from the dealer. (the dealer is 14 miles from my place so plenty of time to see if it will reach operating temperature or not)
 

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Here's something else for you to consider. You mentioned previously that you had contacted Mazda Corporate about this issue with your vehicle. How do you feel about sending them the information from the Russian? It would be certainly be very interesting to see what their response to that would be. It's hard to believe they're not already fully aware of the problem with the seals getting damaged, but I guess there's no way to be sure of that either. Lots of questions and no answers at this point.
 

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Customer support ended up being crap; initially they said they will contact the dealer, make the service manager aware, they will send a Mazda tech there also and all will get sorted; I waited one month and got no calls/emails and reached back to Mazda support which said to go to the dealer as they made the manager aware.
I went to the dealer with printed TSB and they had no clue what I am talking about (they did not get any notification from Mazda or any note in the system).


I already sent them the TSB for reference and my measurements and customer support replied: "I think the technician at the Mazda dealer can shed more insight in the question and your findings about this TSB. I wish I could provide more information, however as I mentioned TSB are more so guidelines for repairs for the dealership"
 

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Well they're certainly not providing any extra help on this one, which unfortunately leaves us lost in space right now. And it's particularly bad for folks like you, who have the issue currently happening on their vehicle. We really need to know if the later coolant valve has the correct seals for this application, IF the problem with the seals is as bad as the Russian claims it is. Nothing but a crapshoot right now.
 

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If they will replace my thermostat again, I'll ask to see if they can give me the old one and I'll be more then happy to ship it to anyone on this forum that has more mechanical engineering knowledge and can open something without breaking it :)

1600miles or January 22nd until my next maintenace so it would be right in the middle of winter where it should be cold enough for them to easily test the car.

A bit offtopic but cars are getting so complicated now (and they are kinda on last-mile with electric cars) that is difficult to troubleshoot.
Take for example SkyActiv-X from Mazda (not sold in US) which is kinda of a unicorn with SPCCI combustion, a mechanical compressor, mild-hybrid, brake-by-wire, etc.

Attached engine bay on my two cars.
BMW is not mild-hibryd but has two batteries (a normal one in the trunck and a Li-Ion one in engine bay), two cooling circuits with two expansion tanks that are black and you can't even check the level, no oil dipstick (only electronic measurement) and no easy way to check brake fluid.
I just trust Toyota when they said they tested this engine very well when thy put it on their Supra.
Car Vehicle Hood Automotive lighting Light
Hood Light Car Motor vehicle Vehicle

Also BMW complicated stuff even more: they installed QR code on tires and somehow is able to "automatically detect them" and I don't know how they do it.
Vehicle Motor vehicle Automotive design Tire Wheel
Motor vehicle Light Automotive mirror Vehicle Automotive lighting
 

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At this point the only way to see is take one apart like the Russian guy did.....
And it would need to be the latest version of the valve, in order to find out if they've switched to something better than those seals made out of ice cream:(
 

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Every time I've heard of someone with any brand car wanting the old part back from warrant work, the answer is essentially: Nope, it's going back to corporate to see what failed.

We'll see what Mazda says if you do ask for it back.

Great post sequence. Thanks for the effort!
 

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European version of the TSB for reference:
Thanks for posting this doc, and it's surprising to me that there is so much of a difference between this and the North American version. First off, this European TSB does not revolve around the P0126, and is focused instead on the underlying problems that owners experience. So in Europe, anyone having slow warm-up and/or heater issues can bring their vehicle in for diagnosis, regardless if the code is present or not. That's quite a bit more owner friendly on the part of the European Mazda organization IMO.

And even more importantly, the European version provides some key diagnostic troubleshooting information that's nowhere to be found in our TSB. And although 2 of those diagnostic steps require the proprietary Mazda M-MDS, the third one does not. It's very much a DIY type of test, and is simply to check if the upper radiator heater hose is hot when the temp from the OBD ECT is in the range of 50-60 °C {122-140 °F}. The upper hose should not be hot when the vehicle in that ECT range, and if it is, that would be an indication that the mechanical thermostat inside of the coolant valve has opened when it should not have done so.

Very helpful to have the temp range for that test identified so clearly, and it's disappointing that Mazda NA is not helping their owners in the same way that the European Mazda group is. Same automaker, same vehicles, and same issue. But definitely not the same degree of effort on the part of those two organizations.
 

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From the European TSB:
4. By monitoring the PID “ECT” using data monitor function of the M-MDS, warm up the engine until the ECT reaches to around 50-60 °C {122-140 °F}
5. Check if the radiator upper hose is hot. If radiator upper hose is not hot, this Service Information is not applicable. Diagnose the heater system according to the instruction in the workshop manual.
NOTE: When the ECT is around 50-60 °C {122-140 °F}, the coolant should not be running into the radiator. The hot upper hose is most likely caused by the open thermostat in the coolant control valve.
My car has been sitting in my garage at ~65F for several hours as a baseline: took it out for 1 mile drive at 30mph constant (exactly 2 minutes drive), stopped, opened the hood and checked the upper hose which was pretty warm (the gauge on the dash was still in the blue area); it wasn't hot that you couldn't put your hand on but it was fairly warm compared with other hoses in that area.

Since my thermostat was replaced twice (although not with the latest revision of the part), can it be ECU just command it to open before it reaches ~190F/90C?
 

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From the European TSB:


My car has been sitting in my garage at ~65F for 3 days as a baseline: took it out for 1 mile drive at 30mph constant (exactly 2 minutes drive), stopped, opened the hood and checked the upper hose which was pretty warm; it wasn't hot that you couldn't put your hand on but it was fairly warm compared with other hoses in that area.

Since my thermostat was replaced twice (although not with the latest revision of the part), can it be ECU just command it to open before it reaches ~190F/90C?
There are no specs in the Mazda FSM related to how the ECM controls the coolant valve, so there's no way to answer your question based on any information that I'm aware of. However, you can plug in your live OBD data reader and see what happens when the ECT value is in the temp range provided by that European TSB. They're saying that if the upper rad hose is hot when the ECT temp gets into that range, then the coolant valve is definitely defective, due to the mechanical thermostat inside the valve opening too early.
 
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