I too own a CX7 March 2010 2.2, though with a 45,000 miles on the clock. we too brought from new and had it full dealer serviced every year (as you can see we do less than the "std" mileage assumed for the car).
My wife passed your thread on to me thinking I wrote it as your engine failure symptoms were identical; Minding my own business, dual carriageway, 60/70mph, no outward sings of any problems then I overheard a tapping sound, did as you did and with identical results.
The fact that I had only just collected the car from a full 50,000 (albeit at 45k) service 3 weeks before left me baffled.
After waiting for the AA to recover I checked the oil, curiously the dipstick showed no oil on it. I assumed the dealer had not carried out the task or re-filled insufficiently....Tried to restart the car and found it seized. AA mechanic some two hours later found the same.
Following this my car was taken home for further outward inspection and then (at my expense) to the Dealer (who had done all the services from new) for a more detailed inspection.
I was somewhat surprised to be told that it could be combustion gases migrating into the oil (by the way it did have oil in it) most likely from the injectors normally no1. a check for this is normally carried out at the 70k service as it can prove catastrophic to the engine if left unattended.
Sure enough with out going anywhere else on the engine the mechanic was 100% correct in his synopsis. No1 injector was caked in carbon (or black flakes just like lime scale) leaving all the others clean. I was then told that what happens is these "bits/flakes" get flushed with the oil into the sump and consequently block the sump pick up pipe mesh filter and ....... effectively cause the engine to have a heart attack.
Some 15 minutes later the sump was removed filter exposed......It looked just like my Nan's tea strainer with the tea still in it..... My poor engine must have been starved of oil because of this...... No oil light ever came on to warn me, changing the oil and filter at the service wouldn't overcome it and nothing far short of me being aware of this or have this part of the service can see how I could have prevented the catastrophic failure of the engine.
The final kick in the teeth was when presenting me with the possible synopsis the Mechanic said "there's a CX engine; same as your over there (6 feet away) with exactly the same problem" !!
My circumstances are similar to yours I would be very interested to know if you found the same reason and what outcome you had with Mazda as I have just stared the journey of recompense, as I am completely flabbergasted at the situation and hold them 100% responsible.
Regards
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