Caravan 3.8l. How did this piston crack?

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Mopar to ya

Mopar to ya

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Any ideas? It came in ses light flashing and running poorly. Misfire on this cylinder. The spark plug wouldn't come out. We warned the customer and proceeded to try and remove it. It broke off in the head. We pulled the head and saw the piston was cracked. And the broken piece is definitely angled down as if it was pushed downward. The valve is intact, as was the plug. Nothing in the cylinder that was bouncing around unless it went out the exhaust valve. Any ideas what might have made it break?
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Just a stab in the dark, but my guess would be that the piston got too hot or had too much pressure in it. Perhaps it was burning lean or detonating? It could have also been just a casting defect in the piston, assuming it is a cast piston.
 
I was thinking this was an act of god, giving a stern warning to those who choose to go the way of the minivan to make other more tasteful choices. but chained360 has a reasonable hypothesis as well.
 
They had it loaded down with 15 fat women trying to pull a hill with a fully loaded trailer of fat women. That'll do it every time.
 
I see two round holes right next to the crack. The last time i saw that a piece of something was bouncing around in the chamber.

This is how it looked upon head removal. No cleaning.
 
Do you have a picture of the head and spark plug? If something was rattling around in the cylinder, it may have left signs on the valves or chamber.
 
It is awfully shiny, did you measure how far down the hole it is compared to the other pistons at TDC. See if it bent the rod too. You'd think if it started to crack at the side it would have just followed along the edge of the thin part of the piston above the ring groove?
 
I'll bet it was running lean, that is why it is so clean, so it probably got hot. The other pistons look like they were running just right.
 
Sucked water or fuel got between the ring and land and ignited repeatedly from leaky injector.
 
I can get pics. The valves are perfect. The plug threads broke off in the head, but all pieces were attached to the plug. that is not a reflection, it is two round holes dented in the piston at the edge of the crack.
 
dano said:
Sucked water or fuel got between the ring and land and ignited repeatedly from leaky injector.
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I was thinking something along the same lines, like the ring getting too hot/being improperly gapped, but usually ring failures don't produce cracks that shape. I'm not sure how a ring/ringland failure would make the piston crack like that. I agree with the fuel buildup and ignition though, because excessive cylinder pressure is the only logical cause (in my tiny little head) outside of a casting defect.

Were there any other stored codes in the vehicle's computer aside from the cylinder misfire? Lean/AF errors? Knock sensors?
 
Thats a saturday night engine.
Piston broke.
That vehicle have more than one driver? I’m thinking rev limiter.

97 intrepid near new came in with cracked pistons. Grandson borrowed car and loaded it up with diesel fuel. Worse it ran, harder he drove it.
 
Got it out, replaced one piston. The connecting rod cap is attached to the rod in such a way you have to loosen the cap bolts and use an exhaust pipe expander to break the cap and connecting rod apart. Runs good now.
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Dude, you dont mess around!
Nice thing about caravans is the pan comes out without a fight.
 
Man, that dude ate something! I melted a pair of pistons once from inadequate fuel and they just melted! No ping, no noise, just smoke. It was quick and painless too; matter of a couple of seconds.

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I am guessing it was on the front bank? That back bank is a pain to work on. Just about to roll over 400,000 km on our 96 gran voyager 3.3. The 3.3 and 3.8 are fantastic engines.
 
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