The piston design is so cool.

 

TL;DW version: He tore the engine down and suspects an overheat that damaged 2 of the pistons and bores. A bit of coolant in the oil. But, pretty perplexed by it still. Not fully sure what happened.

 

Overheat? I wonder if it was caused by the head casting defect TSB much bantered around on the forums.

 

This is all guessing from just watching the video and having personally R&R a 2.5 skyactiv head.
Coolant entered the combustion chamber (unknown from the video or not real clear why ) but it really does indicate excessive carbon built up on the sides of the piston that the scrapers could not clear out which locked the scrapers and compression rings . I am sure had we seen the compression test it would have confirmed this? I would also mention that a lot of the sludge (black not the light brown) in the oil pan had sludge build up form most likely going to many miles between oil changes. So you all just keep following that Mazda oil filter service schedule. lol Oil Analisis I am sure would have confirmed that. Or next time you DIY do your own oil change take a rag and stuff it up in the oil drain hole and twist it around a few times pull it out and see what you find.
The carbon in the intake indicated that there was excessive oil vapor entering the inductive system more than normal. This would have also caused the ring sizers caused by excessive carbon build up on the ring area. The side sckirt damage clearly shows that someone raced the sheeet out of this engine no debate or guessing there.
Remember this is a good video but unless the head is pressure tested no one can guess its true condition. I would have at least run a straight edge across it just to see if anything was measurably off?

I did notice several other things that were either not commented on or over looked but all in all I liked the video!

 

LOL
well nice GUESS but not the same type of overheating that was caused in that TSB. That is why TSBs are not for general public use, you all ( none authorized users of TSBs and or DIY) speculate without enough information and very few have ever built an engine . LOL

 

Hey Callisto, in that video the exhaust ports in the head appear to be smaller then the openings in the header. I say this because of how much of a carbon ring there is on the head.
Have you had the header off, and confirm the header openings are larger then the ports in the head?
Did Mazda do this as anti reversion for exhaust pulses back into the cylinder?

 

See if CS will give you any insight if not then we are all keeping some things proprietary for a little longer.
I will say that the MAZDA exhaust manifold that is so wonderous is not as it seems. But I suppose it does a great job to meet EPA requirement's?

 

Are they trying to do anti reversion?

 

nice try! But guessing is not going to give you any answer right now from me.