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Seems that Mazda has upgraded this service alert to a TSB now, also interesting, now under "repair procedure" Mazda does not mention to check for the DTC, only coolant temperature data.
 

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I might try to go again with this TSB as for me the case "If it is at around 104-176 °F (40-80 °C), proceed to step 2" is still present even at outside temperatures of 77F (the gauge still fluctuates).

I think I might have got a broken thermostat for the second time when they replaced it.
 

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As I got asked by someone, I've done a video with the behavior of my car with the replaced thermostat that still has the issue.

Outside temperature: 65-68F
Start of the trip: 16151 miles (video starts after 1 mile of driving already)
End of the trip: 16162 miles
Total trip duration was 11 miles of driving on the back roads and the engine did not get to operating temperature. I stopped in between at a gas station and the road was uphill and downhill.
(needless to say the other car in the same conditions gets to operating temperature in 2 miles).

Please pay attention in the video at between 07:10 - 09:00 as you will see the temperature needle going down around there. (slight engine brake)
 

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As I got asked by someone, I've done a video with the behavior of my car with the replaced thermostat that still has the issue.

Outside temperature: 65-68F
Start of the trip: 16151 miles (video starts after 1 mile of driving already)
End of the trip: 16162 miles
Total trip duration was 11 miles of driving on the back roads and the engine did not get to operating temperature. I stopped in between at a gas station and the road was uphill and downhill.
(needless to say the other car in the same conditions gets to operating temperature in 2 miles).

Please pay attention in the video at between 07:10 - 09:00 as you will see the temperature needle going down around there. (slight engine brake)
Did you have the climate control unit on during that period of engine braking?
 

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It was on auto but inside temperature was similar to outside and was on minimum fan.
I did some other tests with climate off and it doesn’t affect at all the result.
After about 20 miles of driving it gets to normal temperature and stays there as it should (and this is now in the summer).

I have sent the video to Mazda as well to see if they will do anything.
It will be much easier and obvious in a couple of months when it gets colder.


Sent from my iPad using Tapatalk
 
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Quick update: from the TSB mentioned above, Mazda fixed the thermostat on 16th of November 2020 and they provided a way to check that using the 2D code.
When I tried the first time, I was not able to read that 2D code as I didn't got a clear way of making a photo but today I tried again and finally was able to get the 2D to work.

First of all, these are the instructions from the TSB:
Font Circle Technology Rectangle Brand



What I have on my part (which was the part replaced in February 2021 for which I had to wait 1 month as it was on backorder): PYFD1516Z 201002 2000924
My part seems to be produced on 2nd of October 2020 and the modified coolant control valve is since 16th of November 2020. This confirms that the thermostat that I got, was also the old type.

I've sent the video above to Mazda customer service and they said they will get in touch with my dealership to book another visit and will also send one of their own techs the verify.
 

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...This confirms that the thermostat that I got, was also the old type ...
It will be interesting to see what your coolant temps are reading after they replace it with the newer part. I'm puzzled though why they need to send one of their techs, given that Mazda seems to have completely identified the problem and also the fix. Seems like all they should want to do is have the valve that's on your vehicle right now sent back to them, in order to confirm that it's defective as described in the TSB.

Anyway, hats off to you for hanging in there with this issue and continuing to following up with the automaker(y)
 

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Hopefully it will get fixed and this thread could be solved. Now that I was able to decode the part, I'm more confident that I have got another broken valve.
I think they are sending one of their techs because this would be the 4th visit to the service in one year and they wanna go above and beyond and fix this issue for good (or might be afraid of the possibility for lemon law).

Mazda Customer Support (which was great, btw):
I will recommend that our Mazda technicians get involved to attempt to shed some insight in this matter. This is going to require you to take the vehicle back to the dealer and I will assure that when your appointment is set, accommodations can be made for a loaner


A bit off-topic on why I decided to continue with issue to be fixed: it's an interesting car market now: I tried to do some trade-in for other cars but, even if my Mazda is worth more now than last year, so did the other cars I was looking at and the price delta is even larger than before (and on new cars, at least in my area, almost no discounts/incentives).
 

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Btw, as a comparison (and I know it's far from any precision) but I've done the same test with my other car and it took 1.1 mile and 2.5 minutes to get to operating temperature on the gauge and it didn't matter if it was engine brake as it did not move from there.
Also in this video, outdoor temperature was 61F (a bit colder than 65F with the Mazda).

In the video bellow, I was barely touching the throttle to try to avoid as much as possible to get warmed up quickly.
This is how I remember my Mazda as well from last year.


Before I'll be taking my car to the dealership, I will do a OBD recording with my current thermostat and repeat the route once the car is fixed and I'll post the graph here.
61F this morning and...... another heat-wave going up to 101F on Thursday & Friday :(
 

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I've done the base measurement test with the current thermostat on a route that I can easily repeat after they will fix it.
  • Outside temperature: 70F (21C)
  • Car was sitting in my garage at 80F (26C) (so best case scenario for my thermostat)
  • Elevation gain: 500 feet (170m) in 0.7 miles (pretty steep climb going half throttle and plenty of opportunity for engine to warm up; on the graph is between 07:38 - 07:41 (if curious about the road, it's this one))
  • Max speed: 50mph (80km/h)
  • Trip duration: 13 minutes
  • Trip distance: 5 miles
I will redo the test once they will fix it and add new measurement on the same graph.
283522

I have done the same road with my other car and here's how it looks (this is how I would expect Mazda temp to be as well)
283525

My Mazda thermostat seems to be under 180F which would be in the range of Mazda's TSB as the say the following:
Verify customer concerns and check the coolant temperature in the freeze frame data.
  • If it is at around 104-176 °F (40-80 °C), proceed to step 2.
 
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I wonder if it's this little motor that bad. You can see where it plugs in. From what I read, it opens up to send coolant to different parts of the engine, where the coolant picks up heat. So if it were prone to get stuck, I could see a scenario where the coolant only gets distributed thru the engine to gather heat when the car is on an incline.

283527
 

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I've done the base measurement test with the current thermostat on a route that I can easily repeat after they will fix it.
  • Outside temperature: 70F (21C)
  • Car was sitting in my garage at 80F (26C) (so best case scenario for my thermostat)
  • Elevation gain: 500 feet (170m) in 0.7 miles (pretty steep climb going half throttle and plenty of opportunity for engine to warm up; on the graph is between 07:38 - 07:41 (if curious about the road, it's this one))
  • Max speed: 50mph (80km/h)
  • Trip duration: 13 minutes
  • Trip distance: 5 miles
I will redo the test once they will fix it and add new measurement on the same graph.
View attachment 283522
I have done the same road with my other car and here's how it looks (this is how I would expect Mazda temp to be as well)
View attachment 283525
My Mazda thermostat seems to be under 180F which would be in the range of Mazda's TSB as the say the following:
Verify customer concerns and check the coolant temperature in the freeze frame data.
  • If it is at around 104-176 °F (40-80 °C), proceed to step 2.
To be honest, I have so far been very impressed by your efforts in gathering data, almost like how a test engineer would do... :cool:
 

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I wonder if it's this little motor that bad. You can see where it plugs in. From what I read, it opens up to send coolant to different parts of the engine, where the coolant picks up heat. So if it were prone to get stuck, I could see a scenario where the coolant only gets distributed thru the engine to gather heat when the car is on an incline.
In addition to the actuator that you mentioned, there is also a position sensor which monitors how much the actuator has opened the flap. So if the actual flap opening is not what the ECM commanded and is expecting, then an OBD code should be set and the CEL turned on. So if it was sticking, then the driver should become aware of it.

Mazda did say in their latest TSB that the problem with the coolant valve is caused by 'hollow' areas produced during the manufacturing process. And the hollow areas cause the mechanical thermostat inside of the valve to see hot coolant sooner than it should and open prematurely, thereby keeping the system cooler longer that it was designed to be. Now that's what Mazda says, and although it sounds reasonable to me, no one outside of the Automaker's circle knows if all of that is correct, and if this is the complete story. Time will tell about that.
 
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To be honest, I have so far been very impressed by your efforts in gathering data, almost like how a test engineer would do... :cool:
Thanks. Well, I'm an engineer (software) but that doesn't stop me from reading technical documentation in automotive; if there is a procedure, installation manual or in general any sort documentation, I will read it.
 

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In addition to the actuator that you mentioned, there is also a position sensor which monitors how much the actuator has opened the flap. So if the actual flap opening is not what the ECM commanded and is expecting, then an OBD code should be set and the CEL turned on. So if it was sticking, then the driver should become aware of it.

Mazda did say in their latest TSB that the problem with the coolant valve is caused by 'hollow' areas produced during the manufacturing process. And the hollow areas cause the mechanical thermostat inside of the valve to see hot coolant sooner than it should and open prematurely, thereby keeping the system cooler longer that it was designed to be. Now that's what Mazda says, and although it sounds reasonable to me, no one outside of the Automaker's circle knows if all of that is correct, and if this is the complete story. Time will tell about that.
It's def a wackadoo problem. I suppose you could park it on a steep incline and see if it gets up to operating temp and stays there while parked that way, but even that would provide limited insight. I do now agree this problem is potentially more serious than it first appears. For instance if the coolant is not getting hotter, then that might mean that the rest of the engine is getting hotter than it's supposed to, which would lead to faster degradation of engine parts.
 

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Normal for the 4th Gen to take a long time to heat up... bellow 0c it takes me around 15 min to get up to about middle of the gauge.. When i'm just driving in traffic around 50km/h..... If i'm on the hwy about 5min doing 100km/h with it bellow 0c outside... I know 3 other that have 4th gens and they act the same way... Nothing to worry about its normal..
... My 2006 Mazda3 is like this also. I have found if I do a little more spirited shifting, the needle will move up. And it is fun.
 

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... For instance if the coolant is not getting hotter, then that might mean that the rest of the engine is getting hotter than it's supposed to, which would lead to faster degradation of engine parts.
According to Mazda, this issue a result of the internal mechanical thermostat opening earlier than it should be. And that means that coolant is flowing unrestricted throughout the entire system, which includes the engine. So there's no chance of the engine being too hot as a result of this coolant valve manufacturing defect, assuming everything is exactly as Mazda described in the TSB.

However, the engine running significantly cooler than the design temp for extended periods of time can be just as bad, or perhaps even worse than if it were running hotter. And it's a potentially very serious issue, particularly for the models which don't have a dedicated ECT gauge on the dash. It's entirely possible that some of these engines having a defective coolant valve are running cooler than they should be - not enough to set a code or turn the blue light on, but harmful to the engine nevertheless. And in a case like that, the driver has no easy way to even be aware that the problem exists.

IMO Mazda should be doing a campaign to check the coolant temp on all engines with the older coolant valve installed, and perhaps one of these days they will do that. Meanwhile, I would hope that everyone on this forum seeing this thread, and who has a live data OBD reader, will check the ECT, if they own a vehicle with one of these engines.
 

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Dropped the car at the dealership yesterday, they did a diagnostics and the conclusion was: "looks like the part is starting to fail and we have ordered a replacement under warranty".
The good part is that my coolant control valve will be replaced again (and hopefully with the improved version); the bad part is that the coolant valve was broken from day1 and they did not tested the fix after replacement.
This time I don't need the car quickly so I'll let them replace the thermostat and then test the car before mark it as successful repair.

It will take several weeks to get the part in so expect and update from me late September/early October.
 
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