Is Car Wizard full of it? CX9 head gasket job

It gets better. Did some more looking around. That manifold-as-part-of-head design is unique to the turbo engine. If you look here this is a 2.0L for sale in the ordinary NA configuration. The exhaust side of the head is conventional; there is very little head material exposed to the exhaust flow before it gets into the external manifold.


Here's the problem: By integrating the exhaust manifold runners into the head you now have wildly increased the heat loading -- and differential loading and thus expansion -- on that aluminum casting. You can't deliberately cool that part of it with the engine coolant either because you need the exhaust to be hot when it gets to the turbocharger since that's what you're extracting (the heat in the exhaust) never mind you'd have to wildly increase the cooling system capacity. But this in turn means you've got a huge problem with differential expansion (steel plugs into an aluminum cylinder head) along with heat tolerance in general -- aluminum is just not as tolerant of heating as is steel or cast iron -- and in addition any overheat condition, even a very mild one, is extremely likely to crack or warp the head. Perhaps worse that "runner" offsets the application of mechanical load outward from the edge of the gasket and the head bolts which means you have an even longer lever arm on the above-mentioned gasket, so the "working" potential for the turbo and such hanging off the end of it is MUCH greater.

I have a suspicion Mazda did this because they couldn't vertically fit the turbo into the car otherwise; the 4-into-1 header was too long with a turbo hung on the end so they integrated the runners up top into the head itself, eliminating that vertical space.

I had no idea they had done this although in retrospect it makes sense as to how they managed to fit the turbo in the vehicle. Given what I see there no way would I want one of these engines in my car.

tickerguy said:

IMHO its not fixable @tango

Click to expand...

This must be fixable. If it is not, then Mazda will fail as a company. I guarantee it. Word will get around and then they will fail to sell new, they will fail to sell used, and then they will fail to exist. And if Mazda throws their hands in the air on this then they would deserve to fail.

- particularly if the exhaust runner integrated into the head is part of it -- and I bet it is.

Click to expand...

It is integrated. The video shows this.

If you own a turbo SkyActiv engine vehicle I'd sell the car before the warranty expires. I expect every one of these to fail eventually. And the lever arm problem, while fixable, is not cheap to fix either becasue you probably have to rip all that stuff apart to get to where you need to in order to install a lower mounting brace, assuming the requisite boss to do so (e.g. a mount point on the turbo and the block) exists; I'd have to look at one in detail to have an idea if this can even be done.

Click to expand...

This is not a solution. All that will happen is that the person who currently owns the car can walk away and boast that it never failed while the person who buys it will be all over the forums trying to find a solution that will be solved with ForScan or a Sunday afternoon in the driveway.

Schlep said:

The issue is pretty significant, but Mazda is far from the only manufacturer facing engine problems.

Click to expand...

No, but unlike those bullshit BMWs and Land Rover engines that fail with incredible regularity, the public will not forgive Mazda the same way.

I just hope they do the opposite of what Kia / Hyundai does and actually ackowledge the problem instead of hoping it'll magically fix itself.

Click to expand...

That's some bad company for Mazda to keep, frankly. The idea is to prevent things from happening and take responsibility for poor engineering. Mazda has a reputation for some very interesting things, but for all the effort they put into these things, I don't believe the public is particularly convinced. Renesis, I-ELOOP, Skayactiv-X...all brilliant. But nobody gave a shit. In fact, I am not even remotely happy that Mazda is brining back the rotary engine at all. The inherent problems of that design can never be solved and it will never be as efficient as a conventional engine. But my biggest fear is this new inline 6. What does the head look like? Is the design similar to the inline 4? Will we see similar failures?

@tango what you want and dream of doesn't mean IT IS.

Now I've not examined one of these in detail nor taken measurements and done calculations. BUT -- the issues I see looking at that video are very serious and, from the failures that are happening, not a one-off either.

The two together imply that either (1) the calculations weren't done or (2) WERE done and ignored.

I am especially concerned about those integrated exhaust runners. They're not on the NA heads, and neither is the longer lever arm combined with the much-greater heat cycling problem.

How does Mazda fix it? Well, if there is a place on the turbo and block they can attach a lower support to the block then that's addressable, particularly if you can get to the two places required to attach it without dismantling things as shown in that video. If you have to drop the exhaust to get to it that's not a huge deal (couple of hours) but if you have to rip half the engine bay out its impractical. Assuming that's all there is this is addressable on a retrofit basis at reasonable cost.

The second part however is much-more serious; the exhaust runners in the head were clearly a function of fitting the required pieces in the space available. IF that's the prime issue here, and I suspect it is given that the plugs are reported as leaking too, then the only fix would be to figure out how to use the 2.5L NA head with an external header and the turbo, which would be a complete re-engineering of the turbo system -- an unreasonable ask on a retrospective, retrofit basis.