Poll 2.5T Coolant Leak/Engine Replacement. What can be done to prevent?

Who is having coolant leak issues and have had their engines replaced?

  • Yes

    Votes: 13 28.9%
  • No

    Votes: 32 71.1%

  • Total voters
    45
:
2010 CX-9 GT
Looks like 2020 got the slight bump in torque on premium, so the 2016-2019 all had 310. I thought it was earlier than that. My mistake.

I think that change was actually made for 2021 model. I have a 2018 and it is advertised as 310 regardless of octane.
 
So to circle back to the short vs long block discussion, I just stopped by the dealer with my cx9, and they confirmed that the actual fix is to replace the long block — so their initial statement was wrong. They’re also still telling me it’ll be mid November before the engine arrives and then about a week to install it.
 
In 2018 and newer vehicles this is true. However, this is incorrect for the 2016 and 2017 models, which made 310 regardless of octane.
True on the torque number. As far as I know, there is in fact a difference in the horsepower from 227 to 250 using the different octanes of gas. There has to be at least some more stress on certain parts between the two variables.
Is it enough to make any difference in these particular failures, I do not know. One thing for certain, these failures should not occur no matter which of the octanes that we choose within the manufacture's given parameters.
 

far4ngn

2016 CX-9 GT
True on the torque number. As far as I know, there is in fact a difference in the horsepower from 227 to 250 using the different octanes of gas. There has to be at least some more stress on certain parts between the two variables.
Is it enough to make any difference in these particular failures, I do not know. One thing for certain, these failures should not occur no matter which of the octanes that we choose within the manufacture's given parameters.
The failure as described by the dealer for my engine was a warped head caused by bolts leaking coolant and therefore the head overheating. I've pointed out the bolts in the photo below. These are at the exhaust manifold, so I suspect they changed that part of the head and therefore needed a new exhaust manifold gasket for the redesign.

1634912712570.png
 
So, are you now saying that in addition to the redesign of the "head and exhaust manifold gasket", that there is also a change in the head to where a different configuration exhaust gasket was necessary to mate?
 

far4ngn

2016 CX-9 GT
So, are you now saying that in addition to the redesign of the "head and exhaust manifold gasket", that there is also a change in the head to where a different configuration exhaust gasket was necessary to mate?
I suspect that the modification to the head is related those leaking bolts/plugs and therefore requires a different exhaust manifold gasket. The exhaust manifold bolts on directly adjacent to those bolts/plugs. All speculation at this point.
 
The failure as described by the dealer for my engine was a warped head caused by bolts leaking coolant and therefore the head overheating.
This is interesting because my issue was not described like this. The dealer told me that the block cracked, and that's why I was leaking coolant. I never experienced any overheating, and it was found because I said "I smell coolant" and could have been potentially overlooked for a while longer. Does this mean we're looking at two distinct issues (with different root causes) that happen to have the same resolution, or just different symptoms of the same root cause?
 
This is interesting because my issue was not described like this. The dealer told me that the block cracked, and that's why I was leaking coolant. I never experienced any overheating, and it was found because I said "I smell coolant" and could have been potentially overlooked for a while longer. Does this mean we're looking at two distinct issues (with different root causes) that happen to have the same resolution, or just different symptoms of the same root cause?
I hope there's not more than one issue to bring about possible failure.
My guess is that the problem is not conveyed accurately to the customer.. Therefore we are actually telling different stories due to the inaccuracy of communication from one person to another.
 
:
2010 CX-9 GT
What is likely happening is that the head is developing hairline cracks at the holes where the exhaust manifold bolts/studs go, due to cyclic thermal stresses. That part of the head gets really hot when the engine is running, it is made of aluminum which expands quite a bit with temperature, the manifold is bolted to it and made of a different metal that's expanding at a different rate, and the holes act as a stress risers, so a lot of stress builds up in that area. When you shut it off, everything shrinks back to normal, ready for the next cycle; now repeat that 1000's of times. All that works together to cause fatigue cracks to form in the aluminum and grow. Unfortunately, in this case, eventually the crack reaches the coolant passage in the head and starts to leak.

There are other engines that are prone to cracking in this area, this isn't just a Mazda problem. However, in a lot of other engines the cracks don't make it to the coolant passages so you'd never know they were there unless you were digging into the head for other reasons.
 

far4ngn

2016 CX-9 GT
What is likely happening is that the head is developing hairline cracks at the holes where the exhaust manifold bolts/studs go, due to cyclic thermal stresses. That part of the head gets really hot when the engine is running, it is made of aluminum which expands quite a bit with temperature, the manifold is bolted to it and made of a different metal that's expanding at a different rate, and the holes act as a stress risers, so a lot of stress builds up in that area. When you shut it off, everything shrinks back to normal, ready for the next cycle; now repeat that 1000's of times. All that works together to cause fatigue cracks to form in the aluminum and grow. Unfortunately, in this case, eventually the crack reaches the coolant passage in the head and starts to leak.

There are other engines that are prone to cracking in this area, this isn't just a Mazda problem. However, in a lot of other engines the cracks don't make it to the coolant passages so you'd never know they were there unless you were digging into the head for other reasons.
This sounds like a very viable hypothesis. The original diagnosis I received from the dealer was also a cracked block. Not sure why they can't get their diagnoses straight. The final diagnosis was the warped head and they provided quite a bit of detail regarding it when I went to see the engine and car in many pieces.
 
The failure as described by the dealer for my engine was a warped head caused by bolts leaking coolant and therefore the head overheating. I've pointed out the bolts in the photo below. These are at the exhaust manifold, so I suspect they changed that part of the head and therefore needed a new exhaust manifold gasket for the redesign.

View attachment 304095
Now we are getting somewhere! Thanks for the pic and explanation!
 
I traded in my Focus RS riddled with headgasket recalls / issues - and got CX9 thinking I would have Japanese reliability (and parted with Ford properly with no FoCoMo parts)… I have only done 15000km and understand it will be only low percentage of failures - but truly annoying to hear this
 
:
‘16 CX-9 GT
2016, 80k Miles
I am outside of the factory warranty from Mazda, I do however have an extended warranty. The extended warranty ruled NOT to cover the engine replacement. Mazda USA has decided to cover all costs with the engine replacement even outside of the warranty. This includes parts, labor, and an enterprise rental.
I still do not have my car back from the dealer and it has been roughly 9 weeks, my engines ship date according to the dealer is 6/9/21.
Very glad to hear Mazda took care of you. If it hadn’t already been asked, which extended warranty did you have?
 
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Canada
:
2016 CX-9 GS-L
Maybe we can add an octane used field to this form. I really don’t think it should be a factor, but who knows.....

I think it would be well worth having that data. This would then easily prove my idea wrong once we receive data to the contrary.

Yes I see the value in that, but I think it might be too specific to consider at this point. Like if that's the case, we might as well include details oil and coolant. Unfortunately I also don't think the average owner takes note of those things (accurately) throughout the entire life of their vehicle.

My initial impression was it's a manufacturing issue. The basic questions might give us an idea where those units ended up and/or the relative age of the engine.
 
:
Mazda CX-9 Signature
What outcome are you hoping to achieve by reporting this to NHTSA? This is not going to be categorized as a safety issue. The engine doesn't fail catastrophically, leaving you in a dangerous situation.
Coolant loss -> overheat -> loss of power?
 
:
2010 CX-9 GT
Coolant loss -> overheat -> loss of power?

Let's put it this way: if Ford and Mazda were never forced to recall the V6 because of the propensity for a water pump leak to trash the engine, why do you think NHTSA will step up and force a recall for a cracking issue? I just don't see it happening.