Neither am I (an engineer,) but it doesn't take a genius to know that something causes that fatigue and from what I have seen of/from you, you are NOT stupid either.
Also from your posts and what I know of you, you are concerned about the reliability of the car and do not take chances with it. It should not have failed under those circumstances.
I would be asking for further information from those that would/should know. That's why the comment I made.

 

That is a damm good point.
I don't think anyone at Mazda corporate good give me a straight answer but, like you said, it bares investigation.
I don't "hot-dog" with this Mazda, I have my R/Tfor those times when I feel like putting the pedal to the metal so, the Mazda would never come close to the abuse it would need to crack a motor mount.
I think I want to look into this a bit more.
I am going to call the dealer and see if they still have the one they removed.
I would like to see it's condition.
Bob.

 

If they replaced it under warranty they will not return it to you, as it is property of Mazda Corp. You may only request the return of parts replaced that you pay for and only before the repairs are done, not after, so don't waste your time.
However, you might still ask for a better explaination of the cause of the problem. Be nice and say, "Could you explain to me why a mount would fail under these conditions? I want to understand it better, and how I might avoid such problems in the furture." Play up to them, if you get my drift?

 

Well in another life, I WAS an engineer, so I might be of some help.
The 3 is the descendant of the Protege line; I have a '99 LX (i.e. an SE) 1.8L FP engine, 5 speed manual trans. with 14in. wheels. Compared to the 3 it's lighter, noisier, and bumpier, downright crude, but it is one tough little puppy.
The 3 is the Protege biggerized and gentrified, hence more attention has been paid to vibration and noise deadening. Furthermore, with more use of recycled material, non-critical rubber parts (meaning anything that's not a tire or hose) is likely to have been made from rubber which once upon a time had been a tire or a hose (tire most likely), and been salvaged and recycled.
This means there is a bigger variation in the engine mount, bushing, hanger etc. rubber compound than would have been the case if recycled stuff had not been used.
The result is that while the deflection, damping coefficients, and initial proof loads might have been to spec., the capacity to withstand repeated load and temperature cycling over time can result in the rubber to metal bonding (still half art half science) shearing rather unpredictably, usually by cracking about 1/4 to 3/4 in. away from the bond.
That's what happens when you trade ZOOM ZOOM for SMOOZ SMOOZ and go green I guess.

 

Ya know, I never did ask what part of the mount cracked.
I just assumed it was the metal part, when maybe it was the rubber that cracked.
I will take the advice and ask them what part cracked, and under what condtions do they think would cause this mount to crack.
This was warranty work, so I guess I will never get to see the broken mount.
Speaking of warranties, mine is up in December, and I may want to invest in an extended warranty but, all the plans I have looked at cover $hit that would proably never ever fail.
I don't see one company offering an extended warranty that covers things like brake pads, rotors, exhaust systems, radiators etc.
These are the things that wear out, not crankshafts or camshafts.
When was the last time you had a piston go out?
These are covered by extended warranties.
Most people don't hang on to a vehicle long enough to have these engine parts fail.
Bob.