Hello All -

Owner of a 2019 CX9 with 35.5 k miles (that will be important in a minute).

Love the car have had zero issues. Got 35k service a couple of days ago - totally routine.

this am, I pulled into the work garage and noticed that the check engine light was on (yellow/orange). Car felt fine up till then. Drove it to Mazda dealer, felt fine. Assumed it was a minor problem.

Dealer said code was "cylinder four misfire"; and that the problem was probably an ignition coil or fuel injector. I get a loaner and drive to my office. An hour later I get a call saying THE CAR NEEDS A NEW ENGINE. It will take a minimum of 30 days and maybe longer given, you know, supply chain issues. The service writer couldn't tell me why a new engine but would call me when she had more info.

I searched the forums and found zero info on anything like this. Is this a thing? I thought this model and this year have had exemplary reliability. Thank got it happened now, and not 501 miles from now.

Thanks -

-Alan

 

Our US members may have more info than me, but I believe they can have a head stud issue that snaps or cracks damaging the block. +/or head.

 

Thank you. I looked back at CX5 posts and now see the problem. FYI to those that are interested, this is the 2.5T motor; the earlier posts seemed to talk about the "plain" 2.5 liter.

I'm not so sure that knowing others have had this issue, makes me feel better. My wife has a 2017 2.5L so I hope we do not become a two-problem family. . .

 

I wouldn't worry about the wife MAZDA! Its well into a weathered or season engine now so any hardcore mechanical engine issues are not likely to occur.

I am curious how your engine went from a misfire to determine a hard part breakage like a head stud?? I would defiantly ASK!

 

Yes; I will. I went back to the dealer today to pick up a loaner (a sweet 2021 CX5 signature; guess they are treating me well), and got some additional info from the service rep. There is no TSB or recall. His understanding is that the problem is not in the head itself, but an erroneous instruction to tighten the studs too firmly. Of course, paranoid sort that I am, I suppose that the factory could be trying to tighten the studs more to counteract the warping tendency, and the problem really is in the heads, but this is all just conjecture on my part.

He also told me the problem is principally in the 2019's thru 2021's, and not the older models; and that this dealer (very busy; perhaps #1 in the state of CT although not sure of that either) had had less a dozen instances of this in total. Make of that what you will.

They replace entire engines when this happens, and Mazda supplies new and not rebuilt engines.

As for your question. I don't know; I drove it directly to the Mazda dealer as soon as the check engine light came on (yellow). The car drove and felt normal on the way, through traffic and highway portions of the trip. I suppose it's possible that I had just caught the first inkling of trouble (occasional misfire in cylinder 4) and bad things might have followed quickly had I not acted quickly. Given that the odo read 35,500 miles, I was not taking any chances!

 

There is some problem with a relatively small number of CX-9 2.5T engines with failures as far back as the 2016 model. I have not heard the precise cause, it might be that incorrect tightening spec causing a fatal coolant leak. I have not heard of anyone who did not get a free new engine. I think the coolant leak goes outside the engine, not into the oil sump, so watch coolant levels (check at a consistent temperature) and look for a coolant puddle where you park. That cylinder #4 misfire could have been due to coolant leaking into the combustion chamber...we don't know.

 

Just some information about factory assembled engines. The head bolts are torques in one step all of them at once. The machines that do this have several redundant warning signals if anything is off specifications. Most all the machine I am aware of from the major auto manufactures will shut down the continuing process until the problem has been resolved in the control unit and program.
Generally those engine will be pulled from the line and NOT used by at least the top auto manufactures!

coolant leaking into the combustion chamber enough to cause a DTC would have also caused erratic engine operation and a power level drop. I routinely inject combinations of straight water, water/ isopropyl alcohol, and water/methanol in my intake system and even for fun have increased the water at idle to the point of erratic engine idle ,stumbling and even the engine shutting off and never experienced a DTC.
There is a video I posed doing exactly what I just mentioned.

This is why in another response I was curious how the shop deduced from a DTC misfire that it was a bad engine? Nothing explains or makes sense?

 

There is a history of a small number of these engines having the same failure. While the factory torquing is to spec, if either the spec is wrong or if the materials around the stud to be torqued are wrong (wrong dimension, wrong alloy, etc.), then serial failures can happen.

 

I understand your logic, but if this were the 80's or older sure, not really anymore . I might suggest looking into how engines are assembled in the last 3 decades and specifically in the last 5 years regarding specifically MAZDA's.
The fact that MAZDA has not determined the cause as per TSB.

It is next to human impossible to build a stock engine with all factory parts as good as that assembled using computer controlled assembly machines. Specifically the head to block torqueing because of only one pass on all the head bolt. Humans and most every independent engine machine shop must do multiple steps on single bolts at one time.

I might also toss into the thoughts that most engine parts are produced in large numbers and are not usually tracked. So when a single part may be suspected of the cause like a head bolt it could be tens of thousands of engines effected and not a few again as the TSB suggests.

 

Good info. This is the first thread I have seen about an issue with the 2.5T motor in the CX-5. The NA motor has had issues in some '18 and '19 CX-5's. FYI -you mentioned the mileage being so close to 36k, but the issue you had is drive train so would be covered out to 5yr/60k. Here's to hoping for a speedy fix. If you are really getting a brand new motor that is great news. Enjoy your '21 loaner.