Head Gasket or Cracked Head ?
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TECH Resident
Joined: Aug 2004
Posts: 875
Likes: 2
From: Portland Oregon
Head Gasket or Cracked Head ? Track day today, was going out for the 5th session when my engine started blowing white smoke out exhaust. Smells like antifreeze. LS6 CNC ported GM heads, on a 4.07 bore LS3 block, flat top pistons, road race car. About ten track days on this motor. What is your best guess?? Cracked head, or head gasket. Have not checked compression yet. I did see that the plastic radiator reserve tank has overflowed, so the water is pressurized. 
I wouldn't think block, my suspicion would be gasket and then head since you have ported LS6 heads. Might have cracked through the head casting. I would think the LS3 block would be pretty tough.
If the coolant reservoir is over full then it's not likely a crack in the exhaust port, (guessing) your coolant level would be very low. It took some pressure to get a lot of coolant past the radiator cap if that is the type system you have and into the reservoir. Head gasket?
Thread Starter
TECH Resident
Joined: Aug 2004
Posts: 875
Likes: 2
From: Portland Oregon
Yes, going to check compression first to see what hole is bad. I just wanted to see if anyone has cracked heads, or blown gaskets in a NA motor. 11:1 compression, it's not a radical motor, made 480 RWHP.
Cracks or blown gaskets, is this a common problem.
Cracks or blown gaskets, is this a common problem.
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Leak down each Cylinder.
I was pushing a crazy amount of water our of the RAD cap on the dyno during WOT with a brand new engine. I reused a set of CNC'd 317 heads from my previous engine.
I blew out the #7 cylinder on the next run after dialing it back a little bit.
During engine teardown, I later found a pin hole leak/crack in the head casting right were they CNC'd the runners. (Machine shop confirmed with Vac test) I believe it was just cut too thin and caused this area of the runner to crack, pulling water into the combustion chamber.
I also noticed water in the tail pipe, confirming my suspicions.
Just do all of the necessary checks before running that engine any more. Better safe than sorry IMO, even though it costs a few bucks to do this.
I was pushing a crazy amount of water our of the RAD cap on the dyno during WOT with a brand new engine. I reused a set of CNC'd 317 heads from my previous engine.
I blew out the #7 cylinder on the next run after dialing it back a little bit.
During engine teardown, I later found a pin hole leak/crack in the head casting right were they CNC'd the runners. (Machine shop confirmed with Vac test) I believe it was just cut too thin and caused this area of the runner to crack, pulling water into the combustion chamber.
I also noticed water in the tail pipe, confirming my suspicions.
Just do all of the necessary checks before running that engine any more. Better safe than sorry IMO, even though it costs a few bucks to do this.
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TECH Resident
Joined: Aug 2004
Posts: 875
Likes: 2
From: Portland Oregon
Thanks BlnGTO, that is the kind of experience that I was looking for. What kind of freaky thing could happen. __ Pulled the spk plugs, all look the same, no foul or water. Compression check, all the same, very close on all.
Drained the catch cans, nothing in there to my surprise. How could a steam cloud come out of the exhaust when I started it up ??? A crack in an intake port? Wow, That almost makes sense. Probably time to pull the heads, it's sure not going to fix itself.
Drained the catch cans, nothing in there to my surprise. How could a steam cloud come out of the exhaust when I started it up ??? A crack in an intake port? Wow, That almost makes sense. Probably time to pull the heads, it's sure not going to fix itself.
Yea, I cant offer much more advice than what you already have. Test it, find the cylinder, which tested all good. Now just pull the heads and check the gaskets. If they look good then have the heads pressure tested. If it were the block you would most likely have water in the oil. Which it doesn't sound like you have. So its gotta be a gasket or head. And since yours are ported, they may have a pin hole somewhere.