2016~2023 CX-9 Radiator fan issues

Winnipeg Canada
2017 CX-9 GT
So I've noticed that my engine temp tends to get a little higher than 90C when driving in stop and go traffic. On the highway it seems fine. I took it to a Mazda dealership and they replace my thermostat for $500, but it still does it. Today, it went up to 100C. I popped the hood with the engine running and noticed that the rad fan wasn't spinning at all, even though the engine temp indicator showed it was over 90C.

I fiddled around with what I believe is the ground cable (based on this post), basically just unscrewed the bolt and screwed it back in. I turned on the car and I heard the fan roar to life - something I haven't heard in a while I just realized. So, could it be that simple? A bad ground?

I'm gonna play with that some more tomorrow, but does anyone have any tips on diagnosing this? How to test the ground or test the fan or control module? Tomorrow I'm gonna clean that ground as best as I can, maybe take a photo and post it here. But it might not be that, it could be that fan just started for some other reason so I'm looking for any suggestions now. Thanks.
1) The ground wire connections need to be clean and tight.
2) The overheating could be caused by the wiring to the fan motor, the fan motor, the fan motor thermostatic switch, the grille louvers, the coolant thermostat, or a coolant leak (hopefully not, that would probably be a cracked cylinder head).
3) Make an appointment with the service manager (don't just drive in and talk with one of the service writers) to discuss you paying them $500 for failing to correctly diagnose your overheat problem and failing to fix it. Does Manitoba have any laws about auto repair shops charging for unnecessary repairs or failing to fix the customer's problem? Check that first. And, decide what you want back from the dealership. Your money refunded after they replaced a perfectly good thermostat? $500 in future work credits? Or? It does no good to complain if one hasn't decided what they can do to make it right.
Ya, I took it to the Mazda dealer with the hope they could rule out a cracked head. I have no evidence that the head is cracked, the coolant levels are steady, no coolant on the ground or rear of the engine, and a recent oil change showed no obvious signs of water in the oil.

I think this is just a fan issue, as like I said, it was not spinning at all until I wiggled the ground cable. I'm gonna clean that now and see if that helps. That's the easiest and cheapest fix so might as well try that now. Wish I knew about that before I went to the dealer. But ya, I should go back and demand something.
UPDATE: So I cleaned out the ground, put it back, cleaned up the battery -ve terminal. No difference, the fan will not spin at all. Why it was spinning yesterday for a while is a mystery, however, I notice one thing. If I turn on the A/C, the fan spins and blows a lot of air through the rad. With the OBDII I noticed the engine coolant was 96C before I turned on the A/C, it then quickly dropped down to 90C.

So it's not the power to the fan that's the problem, it's what controls the fan. So what controls the fan? @PTguy suggested a Thermostatic Switch, is that something I can access easy and test myself? A quick google search doesn't really turn up much for that, is there something else that controls the rad fan? Thanks.
Am I over reacting for nothing? Ever since I bought the car, under normal diving conditions the coolant temp never went over 90C, except once last year while driving through the Rocky Mountains and now all the time while driving in stop and go traffic this fall. Looking at the Mazda manual, 100C is "normal".

However, shouldn't the radiator fan be running when the engine is running but the car is parked and the engine temp is over 90C? Or does the fan only kick in above 100C?

Has your CX-9 actually displayed any engine overheating warnings on the dash or anything like that? In the screen Settings area, there's a section where you can see any warnings/errors that have occurred. It sounds to me like your CX-9 hasn't actually overheated.

90C is 194F and 100C is 212F. On CX-9s in the US, the engine temperature is displayed in F (freedom units...I mean Fahrenheit hehe) and 200F is right in the middle of the gauge which is normal operating temperature, so I think your car is actually fine and you got taken by the dealership.

The dealership's service department should know that 90C-100C engine temps are normal and should've told you everything's fine, but instead they used it as an opportunity to take your money by offering unnecessary service. Confirm that you have no overheating warnings/errors in the car's settings and go back to the dealership with the screenshot you posted of the manual showing that 100C is normal temperature and demand your money back.

Regarding the radiator fan, as far as I know the fan will always run when the AC is turned on regardless of engine temperature. I don't however know what engine temp the fan kicks on at if the AC isn't turned on.

Check your coolant level on the coolant reservoir when your engine is fully cold, like in the morning after sitting all night. If the level is close to the L for low, top it off near or at the F for full, but not over it. You can buy the OEM Mazda FL-22 coolant from the dealership and top it off yourself.

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Ok, so I kinda put this on the back burner as winter came around and the engine temp wasn't really an issue. Anyway, last fall I did take it to Mazda and they wasted my time replacing the thermostat which didn't solve anything. I took it back and they think that possibly the rad needs replacing (I doubt it) and that also they think the Engine Coolant Temp Sensor needs to be replaced.

The latter explains why the fan doesn't turn on even when the engine coolant is 100C. But since the fan does operate with the A/C on we can rule out the fan itself. The engine coolant temp sensor sounds like a likely culprit. I'm just not sure exactly where that's located on the engine. Is it next to the thermostat? Is there a way to test it on the car? Is it easy to replace? Any pointers would be helpful. Thanks.

For now I just keep the A/C on and that forces the fan on so I'm not expecting the engine to overheat, but I'd still like to solve this once and for all.

A dealership service department that has acted like a blind squirrel looking for an acorn. They have shown you that they have not earned your trust nor your business.

The engine thermostat is a modulating valve that controls how much hot coolant goes to the radiator to be cooled and how much is just recirculated in the engine to maintain a steady coolant temperature. It has nothing to do with the fan switching on or off. Neither does an (unlikely) clogged radiator. (If the radiator is in fact partly clogged with sediment a radiator shop can clean it, or one can clean it themself with a heavy duty radiator cleaning product and several flushes of water then coolant.) The engine thermostat is a US$29 part plus a US$10 gasket. I think the thermostat is made to begin to open at 88°C (190°F), but I'm not sure. On my car the panel thermometer is always steady just a needle's width to the right of the center line.

The engine coolant temperature sensor is a US$68 part, #SH01-18-840. I'm not sure if that sends the signal to the instrument panel display, which you say is working fine, or to the fan relay, or both.

I'd try a good local repair shop if they have the electrical schematic for your car. If you return to the dealership, use whatever credit you got for them replacing a good thermostat. Always require that they note the problem on the work order, not just the service writer's guess at what parts to throw at the job. Write on the work order that you will not pay if they don't fix the problem. And that you will pay for only the one part and its labor that actually fixed it (plus gasket or seal if needed). Don't pay for a list of parts & labor hours they may put in until the blind squirrel actually finds that acorn. Pay by check. That gives you a day to test the car and see if they fixed it. If not, you have time to tell your bank to stop payment on the check.

By the way, the coolant inside the radiator is supposed to have a temperature gradient from top to bottom. Hot coolant from the engine enters the top of the radiator and gets cooled as it flows to the exit in the bottom.

How about the air shutters in front of the radiator? Are they open when the engine is hot & running and the fan supposed to run? If not, there may be one problem that keeps the shutters and fan from running. And it is not a clogged radiator.
Ya, I'm not particularly eager to take it back to the dealer. I think the problem is with the fan only working when the A/C is on. So I think I found the engine coolant temp sensor, see below.

So I disconnected the cable leading to the sensor and got a P2185 code thrown (Engine Coolant Tempurature (ECT) Sensor 2 - Circuit High). So it seems that's it, but it only throws the code when I disconnect it. Also, when disconnected with the engine running the engine fan didn't turn on. I mention this because according to this video, most modern cars have a safety feature where if the sensor is not working the fan just stays on. So that's kinda interesting.

My question now is, what is that ECT Sensor connected to? I looked at the fuse box and didn't see anything labelled fan, but I'm pretty sure the cables from the ECT Sensor leads there. Any thoughts on that?

Are you reading the temp off the gauge on the dash or from OBD port?

My 2022 flips between centre and one notch past. It has always annoyed me to see it slightly past centre, but no other ill effects.

I just figured it was likely running in the normal range, but the gauge isn't ideally calibrated. Makes me want to use scan tool to monitor now!
Both actually. I know what you mean by slightly past dead center. I've seen it go well past that, and also with the OBDII sensor I recorded temps as high as 100C. But like I said, the temp issue goes away once the fan activates, problem is I can only activate the fan by turning on the A/C. Temp issue also goes away on highway driving as there's just enough natural airflow to keep the car cool.