racecar

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.

vettenuts

iTrader: (4)

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.

96capricemgr

iTrader: (1)

Going to have to pull it apart to find out.

farmington

iTrader: (14)

might want to do a leak down on it before you tear into it to pinpoint which cylinder has the issues

64post

iTrader: (5)

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?

racecar

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.

gagliano7

Its simple but make sure your radiator cap is working correctly.

BlwnLs1GTO

iTrader: (12)

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.

racecar

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.

Taxman20

iTrader: (11)

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.