bubbling in coolant bottle?

[Boog]

I looked at and drove a 2006 GMC today with the 5.3 with 114,000 miles. Just after startup while leaving the lot it started missing a bit and the cel was flashing. After about 2 blocks the engine warmed up, the cel went out and the miss was gone. The truck ran great after that. However when I raised the hood I noticed the coolant bottle was a little low and there was steady bubbling in it. There is no evidence of external leaks.
Question is what are the odds it's got a bad head gasket or cracked head causing the bubbling in the coolant tank? The engine temp remained normal.

[clinebarger]

Get it tested for co2 being present in the coolant, IF there is co2 you have a blown head gasket or cracked head.

This is the type of tester I use http://www.ebay.com/itm/Car-coolant-...Levels&vxp=mtr

Did it ever get hot Anytime in the past? This doesnt usually come out of no where, And 5.3L arent notorious like the Cadillac Northstar, Chrysler 2.7L etc.etc.

The miss & low, boiling coolant sounds like a Gasket/cracked head.

Another way is to pressurize the cooling system to 10lbs, wait for the pressure to drop, Pull all spark plugs, Disable ignition, crank the engine over, If one or more cylinders spit coolant out...You get the idea?

[Boog]

Unknown of history. It's on a used car lot. Temp didn't go above normal while I drove it but after I got back to the lot I raised the hood again to have a look and it was still bubbling. Not boiling but air bubbles. I had hoped it had air in the system from a water pump or hose replacement or something like that and was purging air from the system but I'm leaning toward a head gasket or cracked head. I believe I'll pass on this one. Thanks.

[special-K]

It means compression is getting into the water jacket...blown head gasket or crack in head...or worse,the block. See if there's bubbles in the radiator and/or milky crud on the oil fill cap. It could be too early for either,though.