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I've just recently had my 428 Cobra Jet engine rebuilt. I went through the 2 to 300 mile time on the brake in oil. It did run pretty hot because it was a new motor and it was summer time. But it was under 180 according to the infrared scope. I
Drained the break-in oil and installed all synthetic Valvoline race oil. After the oil change it started running cooler. More within the Comfort Range. I've been driving it and noticing a little bit of leakage out of the water pump. I had to fill the coolant up occasionally because of the leaky water pump. made sure that I had water in it before taking it for a drive. I decided to play around with it a little bit and ran it up on the RPMs for short bursts. Came to a stop at a light. Then started forward as normal. Then poof a bunch of White Steam came blowing out the tailpipes. When I let off the throttle going only like 20 or 10 mph there was less Steam. Then when I throttled it lots more Steam. Of course it started heating up but I shut it down before it got over 180. It started pouring out the Overflow unlike it's done before when the temperature got to that. So I know I have a blown head gasket. But what are the chances that I also have a cracked head? There is no water in the oil. And I haven't done the coolant pressure test on the engine yet. I was thinking of filling the radiator. Water and seeing if there was bubbles. I'm sure there would be. But I haven't wanted to run the engine to see. I'm hoping I didn't crack a head. Is there any way to tell before I pull them? And if there was a slight crack would it be noticeable? Or would I have to have it magnaflux?
 

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somebody smarter than me will be along shortly...
until then:

there's a head gasket on each side of the engine. its unlikely you blew both at the same time, which means you should only have steam/coolant coming out of one tailpipe (i'm assuming you have "true duals", one pipe for each side?)
 

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Discussion Starter · #3 ·
somebody smarter than me will be along shortly...
until then:

there's a head gasket on each side of the engine. its unlikely you blew both at the same time, which means you should only have steam/coolant coming out of one tailpipe (i'm assuming you have "true duals", one pipe for each side?)
I'm very mechanically inclined and I know there's two head gaskets. Yes very unlikely both of them blew out at the same time. The steam's coming out both tail pipes cuz it's got crossover dual exhaust two and a half inch pipe. It's coming more out of the passenger side so I'm pretty sure it's a passenger side gasket that blew out. But my question is what is the likeliness of the head being cracked. And is it most likely that a head will crack before a cylinder wall cracks?
 

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I'm very mechanically inclined and I know there's two head gaskets. Yes very unlikely both of them blew out at the same time. The steam's coming out both tail pipes cuz it's got crossover dual exhaust two and a half inch pipe. It's coming more out of the passenger side so I'm pretty sure it's a passenger side gasket that blew out. But my question is what is the likeliness of the head being cracked. And is it most likely that a head will crack before a cylinder wall cracks?
Impossible to know what cracked (if any) without a teardown.

Likeliness of one or the other cracking first?
Your guess is as good as anyone's

Those heads are known for cracking at the exhaust seat... sometimes...
Does it penetrate water?.... sometimes...

Do the blocks crack?
Well, they are a thin wall casting and if it's been over bored and not sonic checked, then all bets are off.

"Some" of those blocks with a mere 0.030" over bore...
stick a light in the cylinder and it glows thru the water jacket like a Chinese Lantern.

Others can take a 0.060" over bore and be solid.

Has it been over bored?
Did the shop that did the work, sonic check the cylinders?

Sonic check on old FE blocks is a MUST, otherwise it's just a crap shoot if the block hangs together or not.
 

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If you put in hardened exhaust seats , that is the usual area for a problem, The other area for cracking is between the intake and exhaust valves, I doubt it's a head gasket but I've been wrong before.
Randy
 

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I would pull them for sure and probably go with the spare set. They DO NOT need hardened seats installed. The exhaust seats have "work hardened" to the point where they will not have seat recession.
Randy
 

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I've just recently had my 428 Cobra Jet engine rebuilt. I went through the 2 to 300 mile time on the brake in oil. It did run pretty hot because it was a new motor and it was summer time. But it was under 180 according to the infrared scope. I
Drained the break-in oil and installed all synthetic Valvoline race oil. After the oil change it started running cooler. More within the Comfort Range. I've been driving it and noticing a little bit of leakage out of the water pump. I had to fill the coolant up occasionally because of the leaky water pump. made sure that I had water in it before taking it for a drive. I decided to play around with it a little bit and ran it up on the RPMs for short bursts. Came to a stop at a light. Then started forward as normal. Then poof a bunch of White Steam came blowing out the tailpipes. When I let off the throttle going only like 20 or 10 mph there was less Steam. Then when I throttled it lots more Steam. Of course it started heating up but I shut it down before it got over 180. It started pouring out the Overflow unlike it's done before when the temperature got to that. So I know I have a blown head gasket. But what are the chances that I also have a cracked head? There is no water in the oil. And I haven't done the coolant pressure test on the engine yet. I was thinking of filling the radiator. Water and seeing if there was bubbles. I'm sure there would be. But I haven't wanted to run the engine to see. I'm hoping I didn't crack a head. Is there any way to tell before I pull them? And if there was a slight crack would it be noticeable? Or would I have to have it magnaflux?

exhaust gas test on the radiator, and get a regular radiator pressure tester , pull all the plugs get a borescope or a cheap little lizard cam and start looking in cylinders for the coolant
 
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