Help solve the mystery

Me (original owner who has always provided timely, proper car care), my dealership svc mgr, & the CA B.A.R. Agent are wondering… How can a botched transmission repair job caused the pistons on my 2003 Mazda 6i automatic w/127K mi) to get burned-out?

How it unfolded: The tranny guy got my car after (1 dy out of the blue) “D” gear wouldn’t engage. There were NO prior tranny or engine problems, both were fine.

Although the tranny mech denies it I know there shop damaged the engine because

a) (after 3 rebuild attempts) the mech admitted, he couldn’t get the repairs right & I would immediately need to take it to another mech. Took it to the dealership for diagnostics ($160) & they found

a) the engines pistons are toasted.

b) the engine had been filled & overflowing w/ brand new crystal clear golden yellow motor oil. (nonauthorized)

c) the tranny fluid was overfilled & overflowing

d) the tranny vent hose was disconnected.

Please help me solve this mystery.

By the way The tranny shop was sited by the B.A.R for doing unauthorized work on the car & trying to charge me for it.

Shoot! they even replaced the CV boots for some unknown reason & put it on the invoice as “No Charge”.

Ref: My car was driven by shop for a total of 16 mi. over a 2 mo period.

So what do you think guys?

Perhaps the shop did more than a trans job, perhaps they did a motor switch? Can you document the motor in the car now is the original motor? Something very fishy going on.

About all you could do to damage the motor in 16 miles would be to take the car to Laguna Seca for racing or track day.


Wrong fluid drained while working on the car, and engine started with no oil in it.

Poured in new oil after clanking noises heard.

CV Boots might have been torn while removing and replacing the transmission.
That’s a not too expensive freebie.


That sounds like a great educated guess to me. I second the motion!

I like Bladcutter’s theory.
In fact, no other explanation makes sense to me, given the circumstances.

I’ll pose an alternate theory: if a 2003 Mazda uses a vacuum modulator, the clown plugged the vent and overfilled the tranny, allowing tranny fluid to be forced into the engine’s intake and burned. Tranny fluid in a cylinder will preignite something awful, and could easily burn holes in the pistons.

The pressure probably blew the seals and required replacement of the seals…and that may be why they put in new half-shafts…

I’d be interesting in hearing Transman’s thoughts. Hopefully he’ll stop by for a visit.