Hello everyone,

First time poster. I own a 2016 CX5 with 80k miles, AWD. The symptom started out with major oil leak. Went under the car and found out that the oil pan was leaking. The leakage was through a puncture/crack in the pan, like someone punched the oil pan from the inside out. With the oil pan off, it was evident that an engine block bolt got broken off and was sent flying around, smacking the oil pan on the inside in the process. As you would probably knew, the CX5 engine block is made up of 2 halves, the top half and the bottom half, mated together by 10 bolts.

This pic is the view of the engine looking up at the crankshaft.


Here is a pic of the bolt's head fished out from the oil pan, which is in the background



Here is a pic of the scorings on the crankshaft counter weight




I'm so surprised that a stationary bolt like this engine block bolt could be broken off. If anything I thought it would have been a connecting rod's bolt that snapped due to the reciprocal nature of the piston. Clearly this is a defective bolt. Has anyone heard of such an issue with the CX5? The car is at a dealer right now for assessment. The car drove just fine with that broken bolt. No vibration. We're thinking about reaching out to Mazda to see if they could give us some assistance. Planning for the worst, we don't want spend the $ to replace the engine so we are thinking about extracting that broken bolt and put a new one in its place (maybe going with a hardened grade bolt instead). Does anyone have the torque spec for these bolts?

TIA

 

Welcome to the forum..

 

Mazda , well based on the pictures and other information it’s well out of warranty. I won’t post further because I have been on both sides of similar engine situations over the years. So I know from experience being in court how it’s will end up. Let’s say no settlement.

As for removing that stud without doing it the proper engine tear down, well you will get one chance of extracting it. So hopefully the person doing it has done them before. At least with experience it is 50/50.

The fastener being defective, I can tell from the pictures you posted of the oiled saturated bolt head. Nor is the mounting areas clean enough to make an assessment either. But if I were a to defend at 80k miles if the machining was faulty it would have been on more then one engine and as those bolts in that area are all installed and torque in one step by a machine the monitors close specification it would be difficult to defend. And as pointed out that areas unless the engine was used for competitive spores or run at very high frequent RPM that can distort an engine block then it’s another not so in favor of manufacturing defects.
But I do hope that you get a sympathetic reader at Mazda corp that may give some form of any compensation.
Please keep us up to date as this kind of threads are always of interest
BTW the Torx head bolt is a harden bolt that exceeds 10.8 / grade 8 specification
Now as a former owner and builder of a performance engine machine shop….building a better mouse trap to prevent “cap walking” would have used high strength studs and nuts like through ARC . And possibly a custom girdle or at least a few added Tig welded braces.

 

Have you owned this car from new?

 

We bought this car new and it has been driven by a HS girl, now in college/post grad school. She doesn't race or abuse the car and the car is well maintained. The puzzle is how could this bolt/stud break of like that???

Knowing that this car is out of warranty and a slim chance Mazda will replace the engine at no cost, we do not entertain litigation. But hopefully if we could convince them of their defect, perhaps they could offer us some kind of compensation as a goodwill gesture.

As I've mentioned, since the car drove fine even after the bolt broke off, we're willing to go the path of installing a new bolt. Hope by chance someone on this forum knows the torque spec for that bolt.

 

Honestly sounds like you guys got really unlucky with that bolt failing. If it were a defect issue, there probably would've been a lot more bolts doing that at the same time.

 

Sorry there is a big reason why I will not provide that info....
I recommend you should use a Mazda or ALLData service guide or a universal torque fastener chart for that part is because the proper install is all with a specific pattern torque setting sequence. Technically speaking on that specific part you could create a problem instead of curing one.

At any rate its your engine.

ALLData has the correct factory specification for that part but it is a small fee which IMHO will have more valuable service information about your service project.
Single Vehicle Subscription | ALLDATA


You first challenge is to remove the stud to replace it!

 

I found a Facebook post that also detailed the same problem I have, the broken bolt. Not the same bolt but a similar one that was more toward the middle of the engine. The poster replaced the bolt and continued on with life. The post was made in 2024.and the poster said that apparently the bolt was no longer available from Mazda. This matched with my experience yesterday when I stopped by a local dealership. However, the poster said that you could buy a replacing bolt and the spec for that bolt is M10-65. Also from my visit to the dealership and asking them about the torque specs, I came to know that the torque spec is 75 foot pounds.

Not sure if anyone has posted this but in my search for the torque specs, I came across this post on another site. The post has a link to the repair manual for the CX5 with torque specs as well! Too bad it doesn't have the information I was looking.

https://mazdas247.com/forum/t/free-w...-kf.123878000/

 

That's really helpful info!

 

The one thing about forums and DIY serving in any capacity is that when you find a member on any given vehicle forum post a less then the proper way to do something and claiming it worked you almost NEVER find them posting that that work, they did fail. So, the other DIY readers think that it worked, and they should follow the service.

In this thread it's a no brainer .... talk to any good quality engine machine shop see if first if they would do what is thought to be a sound repair face to face and see if they are going to guarantee it will work.

As for Mazda and another auto manufacture that sells vehicles in the USA it is required that they carry replacement parts for 10 years from the date of the VIN production date. The exceptions are parts like fasteners (considered universally and non-s[pecifc available) for internal engine replacements. There is actual a long-written explanation as well but anyone can find that info or pertaining to Mazda contact Mazda USA.