Two cracked heads Merc 5.0L EFI

[capton1]

#4 and #5 cylinder heads, cracked thru the exhuast valve seats
very odd that both would be cracked, operated then when shut off, would not restart
due to hydrolock cylinder, drain, cylinder, would rerun until shutoff
what's the chances of cylinder opposite each other cracking and due to ?

 

[Scott Danforth]

Re: Two cracked heads Merc 5.0L EFI

chances are you lost the head gasket between the two more so then a cracked head

 

[PiratePast40]

Re: Two cracked heads Merc 5.0L EFI

Sounds like thermal shock. If the engine was hot and then you had water backing up into those cylinders, then cracking from the abrupt change in temp makes sense to me. I've seen heads cracked from the exhaust valve seat into the valve guide from an overheat.

 

[Bondo]

Re: Two cracked heads Merc 5.0L EFI

what's the chances of cylinder opposite each other cracking and due to ?

Ayuh,... As Pirate says, a short lack of water flow can cause hot spots, 'n when the water comes back, the castings crack from thermal shock...

Not at all Uncommon...

 

[yamatech43]

Re: Two cracked heads Merc 5.0L EFI

intresting thing here is he says "operated and turned off" then problem.....wonder if flappers are good and also headers are at proper height above waterline....

 

[Don S]

Re: Two cracked heads Merc 5.0L EFI

chances are you lost the head gasket between the two more so then a cracked head

'

cylinders 4 and 5 are on opposite sides of the engine.