Drive Belt Snapped, Engine Overheated (2018 CX-5)

[andwhatarmy]

As the title says, the drive belt for the coolant pump on my 2018 CX-5 snapped, and my engine overheated. Now both belts and the auto tensioner are being replaced under warranty because I had them put on less than 8 months / 10k miles ago. That replacement was mostly preventative, there wasn't a catastrophic failure like this or anything, but the shop was telling me then that the factory original tensioner was leaking, as the TSBs say can happen.

This is a question about what to do next.

The shop showed me an image of coolant leaking from a small-ish hose clamp. When the engine overheated, there was a lot of coolant splattered all over the engine compartment, I suspect the pressure caused the reservoir to overflow and splatter. It seems reasonable to me that some hoses would leak a bit in that condition, but should be fine otherwise, I would think. The shop wants to replace the "coolant control valve" (if this could refer to multiple components, I don't know which one they mean by its full name, but it is pictured) and do a coolant flush.

Is there any reason to think that the control valve actually needs to be replaced? The engine was only overheating for a brief time, I pulled over immediately and got a tow truck.

If I do not get the control valve replaced, does the 2018 CX-5 have an indicator light that will reliably tell me if my coolant gets low? Or would I need to check the coolant level on a cold engine regularly? I am not sure how full or how low the coolant is in the reservoir. I am going to ensure that the shop tops it off before I pick up the car regardless.

Ninja update: As I was writing this post, the shop called to say that they are only replacing the belts under warranty, not the tensioner. Two hours after they sent me the estimate, suddenly it is no longer leaking. I guess when they thought I was going to pay for it out of pocket, it was leaking, but now that it's a potential warranty replacement it's actually working fine.

 

[cz5gt]

I would rteplace the valve. Now is the right time since coolant is changed too. there is tsb for it also. See if you can go through warranty.
Since tensioner got replaced recently , no need to change it. If I am reading your post correctly.

I would be more worried of the overheating though. That can cause other sort of problems down the road.

Was your water pump belt replaced too recently? Its quite strange for it to snap out of the blue. That belt is so simple and almost no tension there, so it should last a lot of time unless there was other reason.

 

[andwhatarmy]

@cz5gt Is 01-011/21 the TSB you are referring to? I haven't had those problems with my car. The dealer shop has not explained to me why the valve needs to be replaced other than "leaking", but they pointed at a hose with the leak, not the valve. My car is just over 90k miles, very much out of the factory warranty, so getting a replacement by just citing this TSB might be difficult. Unless there's a different TSB you were thinking of?

Yes, you read my post correctly. They are not replacing the tensioner today at all. But I'm irritated that they wanted me to pay for it at first, before I pointed out this was a warranty problem.

I hope the overheating was minor, it only happened once, for very short time before I was able to pull over and turn off the engine. But the temperature indicator was definitely maxed out when the error went off.

Both of the belts and the tensioner were replaced in April 2023, less than 8 months / 10k miles ago. Yes, I agree it is very unusual for a belt to fail like this. In August 2023, the dealer replaced a cracked cylinder head - this has not been my year for saving money on car repairs. My theory is that during that major repair, the drive belt was damaged or not put back on correctly. But that's just a theory.

 

[cz5gt]

Yes this one and I think there was another one.
The newer valves are revised.

the whole valve concept is stupid and its because of the cylinder deactivation feature. On mine it lags to open so sometimes the car goes to higher temp before it fully opens.
If you are out of warranty (assuming valve is working as expected) then it may not be worth it as you have to pay for everything. Its costly from what I recall.

Sad to say but if the car overheated badly may be its worth thinking about tradein to a new one at some point.

 

[edmaz]

IMO your most important consideration at this point is grilling the shop to identify why the belt snapped. It's hard to imagine even an incompetent shop making a mistake on the install, but perhaps they left a tensioner bolt lose, or some other stupid thing. Or it could be a case of them using an incorrect replacement belt, which you naturally would not want to be repeated again.

Right behind that concern is the potential damage to the engine from the overheating. the usual suspect when an engine overheats is a head gasket failure, so you need to monitor your oil and coolant (in both places) very frequently. This shop would be on the hook for any engine damage as a result of the overheating, but getting them to agree to that might be another story.

The coolant control valve TSB is actually related to the mechanical failsafe thermostat opening prematurely, resulting in the engine not heating up quickly enough, which has nothing to do with your situation.

You probably just didn't notice the red battery light coming on after the belt snapped, correct? Also no CEL, or audible warning during the entire event?

 

[Silly Wabbit]

Could you specific if the replacement parts were OEM or aftermarket? I ask because in my experience, "new" aftermarket parts can still be a gamble.

 

[stickerbush]

You probably just didn't notice the red battery light coming on after the belt snapped, correct? Also no CEL, or audible warning during the entire event?

Doesn't the water pump have its own belt with the alternator etc. being on the serpentine belt?

 

[edmaz]

Doesn't the water pump have its own belt with the alternator etc. being on the serpentine belt?

My bad for misinterpreting what the OP wrote. Reading the part about both belts being replaced, I just assumed that one belt whipping around took out the other one.

 

[andwhatarmy]

@edmaz I would love to get the shop to explain why the belt snapped. They are not forthcoming with any explanation unfortunately.

When I posted on Friday, I didn't explain what happened when the belt snapped. It was completely without warning. I was on the highway, and suddenly the dashboard lit up with warnings. The red thermometer light went on solid, not flashing. An additional engine overheating message appeared on the dash, and the ECU cut the engine power to limp mode. I was able to pull over immediately, and I switched the display to show the thermometer indicator which was constantly jumping around between just-below-red-zone and max-of-red-zone. At that point I got a tow truck. I never heard any sounds coming from the engine, even when the tow driver started my engine to get onto his flatbed.

In the image you can see both belts on the engine, with the water pump belt just hanging out. And next to it, you can see how the water pump belt was fairly shredded.

Thanks for the advice. The shop filled the coolant before giving me the car back. I am monitoring my coolant to see if there appears to be any leak. I am thinking that at minimum, getting a coolant flush is a good idea in the near future, since I have heard that after overheating there is a risk of the coolant becoming acidic?

@Silly Wabbit The replacement parts have all been OEM. All the service has been at the dealer. Only exceptions are the wipers and battery. And I replace the air filters myself, but with OEM parts.

 

[yrwei52]

@edmaz I would love to get the shop to explain why the belt snapped. They are not forthcoming with any explanation unfortunately.

When I posted on Friday, I didn't explain what happened when the belt snapped. It was completely without warning. I was on the highway, and suddenly the dashboard lit up with warnings. The red thermometer light went on solid, not flashing. An additional engine overheating message appeared on the dash, and the ECU cut the engine power to limp mode. I was able to pull over immediately, and I switched the display to show the thermometer indicator which was constantly jumping around between just-below-red-zone and max-of-red-zone. At that point I got a tow truck. I never heard any sounds coming from the engine, even when the tow driver started my engine to get onto his flatbed.

In the image you can see both belts on the engine, with the water pump belt just hanging out. And next to it, you can see how the water pump belt was fairly shredded.

Thanks for the advice. The shop filled the coolant before giving me the car back. I am monitoring my coolant to see if there appears to be any leak. I am thinking that at minimum, getting a coolant flush is a good idea in the near future, since I have heard that after overheating there is a risk of the coolant becoming acidic?

@Silly Wabbit The replacement parts have all been OEM. All the service has been at the dealer. Only exceptions are the wipers and battery. And I replace the air filters myself, but with OEM parts.

Your experience is very strange especially when you said the belt replacement service was done by a Mazda dealer with all the OEM parts.

I was worried about the filling up the coolant part but your Mazda dealer should have used Mazda FL22 coolant which is pretty expensive and most indies may not want to use it. But yes, once you have lost factory FL22 coolant, the manual says the replacement interval will be cut into half. An earlier engine coolant flush with fresh FL22 coolant should be considered.

I do have overheating experience a couple of times on my 2000 BMW 528i. The first time the plastic water pump disintegrated into piece at 28K miles. The second time the serpentine belt snapped due to an idler disintegrated which damaged the belt. Both times the car got driven for several miles to get home, and the engine is still fine so far even though the engine temp gauge was in the red zone. Of course different engine may have different results. And the use of Castrol full synthetic oil on the 2.8L I6 could have helped too.

The invoices from your Mazda dealer should tell more stories. Do check your invoices for these services and if you can post them here that would be great!