Cylinder 6 Meldown

[Brian-17S550]

Looking for a little help on what could have caused this. Boosted 17 Coyote on 93 pump. (I know, I know). The night before I was going to install a Fore fuel system for E85, I decided to take the car out for a drive. A mile away from my house I did a good pull and the car lost some power. I pulled over and didn't notice anything major going on. I got it home and by the time I made it, I was pushing white smoke from the exhaust. I did a once-over and noticed that my intercooler overflow was empty. Pulled the lid and found that I had a leak in the intercooler core. Whipple replaced it under warranty. I installed my fuel system and got everything back together. On first startup everything seemed fine. But once it warmed up, it was billowing white smoke and I knew something was off. I ended up tearing it all apart after a compression test showed zero compression on #6. Once I pulled the driver-side head, I found the piston in 6 had melted and caused some pretty deep scoring at the top of the cylinder.

I am trying to wrap my head around what happened. I somehow got a leak in my intercooler and melted a piston at the same time. Could too much water going into the cylinder from the leak cause this to start? Maybe it messed up a ring and I didn't catch it in time?

Bad fuel is a thought, but that doesn't explain the leaking core. Fuel injectors were fine btw. I had them checked and they were not clogged. Also, it was not a tuning issue. I've been running the same badass tune for well over a year.

Any feedback would be appreciated. Currently getting everything I need to get it going again, but I was looking for an idea on what could have happened.

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[SheepDog]

What do the other pistons look like? That one has clearly seen some water/coolant considering how clean it is. Was the cooling brick leak directly over cylinder #6?

 

[Brian-17S550]

It was leaking from the top side somehow. But, when I first pulled the lid, the water seemed to be pooling in the #6 exhaust valve area. So I first guessed that I had an issue there. 5 & 6 in the first picture, 7 & 8 in the second.

 

[SheepDog]

Not much else could melt a piston like that, aside from going lean. What does the lower intake gasket/cooler plenum around #6 look like?

 

[Brian-17S550]

Under the head gasket on the block?

 

[SheepDog]

Under the head gasket on the block?

No, the gasket under the supercharger's lower intake portion that has the Cooling bricks in it. Where it meets the cylinder head, and intake port (what blower do you have?)

Im wondering if unmetered air was being sucked into cylinder #6

 

[Brian-17S550]

Ahh, gotcha. Gen5 whipple. I didn’t notice anything off there. I can double check it it’s buried in the garage.

 

[SheepDog]

Ahh, gotcha. Gen5 whipple. I didn’t notice anything off there. I can double check it it’s buried in the garage.

Look for a damaged gasket. Also look for a damaged injector o-ring, or any signs where unmetered air could have been sucked into #6.

Coolant/water in small amounts actually prevents detonation, and would have cooled the cylinder, so the melting you are seeing likely isn't a result of the coolant leak from the supercharger cooling system. Larger amounts would have hydrolocked the motor in that cylinder, but generally bends or breaks a connecting rod

 

[furdfan2018]

Lean condition. Could have been some bad gas, leaking gasket/o ring, too much ignition timing for octane provided, low fuel in fuel tank, poor #6 injector performance.

 

[HKusp]

#6 is a culprit many times. CoryS had #6 on two different builds. Mine was #6. Pull that piston when you get a chance and see if the ringland is broken. If you do long pulls, or back to back pulls on 93 and stock ring gap, that's what happens.

 

[GregO]

#6 is a culprit many times. CoryS had #6 on two different builds. Mine was #6. Pull that piston when you get a chance and see if the ringland is broken. If you do long pulls, or back to back pulls on 93 and stock ring gap, that's what happens.

It’s on the cold side, not a hint of damage on the hot side of piston.
How is the Roush SC avoiding this ? We know they’re not regapping rings, correct ?

 

[hlfbkd420]

#6 is a culprit many times. CoryS had #6 on two different builds. Mine was #6. Pull that piston when you get a chance and see if the ringland is broken. If you do long pulls, or back to back pulls on 93 and stock ring gap, that's what happens.

Yup.. Same thing for me. Roush P2 on my 2019 blew the ring land on cylinder 6 at 21,000 miles. Not sure when it started but I drove it hard on a Friday night and then to work on Monday and Tuesday. When I left work, I started the car and it immediately had a CEL. Drove it home and read the codes, it was misfiring on 6. If you took the car about 4,000 RPM it billowed smoke out of the exhaust.

Car is still on 91 but will be converted to E85 soon enough. Hopefully I don't kill my 2nd engine before then. I've put 7,000 hard miles on it since the swap.

It’s on the cold side, not a hint of damage on the hot side of piston.
How is the Roush SC avoiding this ? We know they’re not regapping rings, correct ?

See above. I doubt they are but I wouldn't know because my aftermarket warranty wouldn't allow the dealer to rip the engine apart to see exactly what was going on. Roush wouldn't cover it because of headers and a tune. I don't blame the tune. Roush's tune sucks. That's WHY they avoid it. They may be safer but the transmission tuning is awful.

 

[SheepDog]

The moral of the story here is this: Stock motor with stock ring gaps on pump gas = You're gonna have a bad time, especially with PD blowers where heat is already an issue.

 

[GregO]

Yup.. Same thing for me. Roush P2 on my 2019 blew the ring land on cylinder 6 at 21,000 miles.

Blew the ring land ?
Cracked and broke away or melted ? Same area as OP, intake side of piston ?

 

[HKusp]

Most of the regular posters have seen mine many times, but I'll put it here for the sake of having info in this thread as well.

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