2016~2023 Engine clunk upon shutdown in cold weather

sm1ke

2018 Mazda CX-9 Signature
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Canada
I figured I'd post this since it doesn't look like anyone here has experienced this issue yet.

Since the car is going to the dealership for a coolant leak issue, I figured that I'd also ask the service manager to look into an engine clunking noise that only seems to appear when the car is turned off in cold weather. Since moving back to Manitoba, where it gets much colder in the winter than where I lived in Alberta, I've noticed that in cold temps (usually -20c or colder), the clunking noise appears. See video below (notice the odometer shows just over 17k kms, currently the car has over 65k kms).


The clunk may be a little hard to hear because I had the doors closed in the video, but it's much more audible with the door open or the windows down.

I have not noticed any significant changes in drivability or performance, so I've kind of lagged on getting this looked at until now. Anyway, as soon as I mentioned this issue, the service manager suggested that it's likely a frozen motor mount, which actually makes a lot of sense. He said that the CX-9 uses oil-filled mounts, and that they are prone to freezing up in extreme cold. We recently had a few cold snaps here (-35c to -40c), so it sounds like the mount(s) have just frozen up again.

We'll see what they find after they take a closer look.
 
@Glaucus, I know you have a 2017 and that you also live in the same city. Have you ever noticed this noise on your car?
 
sm1ke, have you been under the hood when someone else shut the engine off? Or the car on jack stands and you've been underneath when it was shut off? Something is loose & banging due to the normal (or maybe excess) shudder of the engine stopping. The cold changes dimensions, of course. Engine mount getting ready to fail? Exhaust hanger not tight enough?
 
sm1ke, have you been under the hood when someone else shut the engine off? Or the car on jack stands and you've been underneath when it was shut off? Something is loose & banging due to the normal (or maybe excess) shudder of the engine stopping. The cold changes dimensions, of course. Engine mount getting ready to fail? Exhaust hanger not tight enough?

Not quite, I've had the hood and door open with the engine running, and hit the engine stop switch then moved to the engine bay to try and pinpoint where the noise was coming from. I wasn't sure what it could have been until now. Exhaust hanger could also be the culprit, but I don't hear it banging around when I drive over rough or ice-rutted roads. The noise is only apparent when I turn off the car, otherwise everything sounds pretty tight.
 
Frozen active grille shutter maybe ? They go to the fully opened position when the engine is turned off.
 
Frozen active grille shutter maybe ? They go to the fully opened position when the engine is turned off.

The sound seems to come from an area closer to the firewall, not so much near the front of the car. But I'll take a look to see if anything is visibly frozen later.
 
@Glaucus, I know you have a 2017 and that you also live in the same city. Have you ever noticed this noise on your car?
Hey Smike. Ya, mine has endured the same cold as yours but no, I've never heard that. I will keep my ears open for that though. Is it just after you hit the engine Stop button?
 
Ok, I just listened to it now. Not sure how I'd categorize that sound, but it sounds like something that was spinning is coming to a stop after rubbing up against something. If it were a bad/frozen engine mount you might be able to feel it vibrate the entire car.

If you go for a long drive, so that the engine gets nice and hot, do you still hear that when you shut it off? If so, frozen anything is probably not the cause. Almost sounds like a fan or something that's off balance.
 
Ok, I just listened to it now. Not sure how I'd categorize that sound, but it sounds like something that was spinning is coming to a stop after rubbing up against something. If it were a bad/frozen engine mount you might be able to feel it vibrate the entire car.

If you go for a long drive, so that the engine gets nice and hot, do you still hear that when you shut it off? If so, frozen anything is probably not the cause. Almost sounds like a fan or something that's off balance.

Yeah that sounds like an accurate description. My drive home is usually 25-30 mins and I still hear it once I turn the engine off in the garage.
 
Tomorrow will be a lot warmer than today. If it still does that, with temperatures around 0C, we might be able to rule out cold weather.

What spins and only comes to a stop with the engine off that's located by the firewall? I can only think of the turbo. Other things it could be: some belt driven accessory. Maybe a bad pulley?
 
Tomorrow will be a lot warmer than today. If it still does that, with temperatures around 0C, we might be able to rule out cold weather.

What spins and only comes to a stop with the engine off that's located by the firewall? I can only think of the turbo. Other things it could be: some belt driven accessory. Maybe a bad pulley?

No idea, lol. All I can say is that the noise is quite noticeable in cold weather. In warm weather, when I turn it off, all I can hear is the electrical system humming until the lights turn off automatically.

The car is going to the dealership at the end of next week. Hopefully I'll be able to provide a better update when I pick it up.
 
Have you tried turning the AC system off? I agree with what @Glaucus mentioned it sounds like a fan or something coming to a stop after the system is shut off.
Possibly the interior HVAC fan?

It doesn't help that I have someone outside building a Gazebo and the hammering noise sounds almost exactly the same!
 
I haven't tried that yet. You guys may be right, could be a bad pulley or the HVAC fan. I'll try to remember to turn the HVAC off a few minutes before I get home to see if the noise is still there upon shutdown. Maybe the cold temps are causing some tolerance changes in a pulley or fan that result in the clunking 🤷‍♂️
 
I have a clunk but on the non turbo cx5. Anytime I stop the car in the garage when it super quiet. Sounds like a relay shifting after the engine stops but kind of metallic sound. Been like that since day one. Havent noticed if it happens only when its cold though and Not sure if yours is the same. Will start to monitor it and see if there is a pattern.
 
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