Head gasket seems ok, but coolant was bubbling...Why?
 

:confused:

Awhile back, I overheated my 96 LT1 because the splines on the WP drive dowel stripped. Trying to find the extent of the damage, I was noticing bubbles in the radiator with the rad. cap off, so I assumed I f***'d up the head gaskets. (No other symptoms of a blown HG though.) I pulled both heads, and the gaskets look fine...no signs of burn-through. I checked the heads with a straightedge, they are both flat to within less than .0015"...I counldn't get my .002 guage in at all. None of the spark plugs were white. Any reason why I would get bubbles in the radiator?

Keep in mind the water pump was not spinning at all when I was seeing bubbles.

Bubbles would only appear after the engine was about 200* or so, and would appear maybe 5 seconds after being started without the radiator cap and warmed up.

Do you think I had air in the system that was being forced out? If so, how would it have gotten there?

If the HG blew, why would I not see where it failed?

I want to get the car back together, but don't want to have to go through this again when I do.

Thanks again all.

Re: Head gasket seems ok, but coolant was bubbling...Why?
 

With regular coolant and no coolant circulation around the cylinders, coolant can boil. My guess is you were seeing bubbles for that reason. Usually when you see bubbles in the radiator it's becuase you blew a head gasket into a water jacket, but in your case I think you just have excessive heat in the coolant around the cylinders since it isn't flowing.

I dont know if you blew a gasket or not, but it's possible one was seeping a little bit. Also possible you have a slight crack in a head, though with alouminum I doubt it. If you hav the heads off already, you can have them checked for cracks and straightness, replace your head gaskets, and after you reassemble, have the system pressure tested. Some mechanics and shops have pressure testers they can use to test your cooling system for leaks.

Re: Head gasket seems ok, but coolant was bubbling...Why?
 

have you had the heads checked for cracks?

Re: Head gasket seems ok, but coolant was bubbling...Why?
 

Thanks for the reply.

No, I have not had them checked for cracks yet. There's a shop not too far from me that can check them. What should I expect for $$?

Re: Head gasket seems ok, but coolant was bubbling...Why?
 

Dont know what they cost up there, but down here it's roughly $35, unless the head are filthy then you need to clean them first. Another $35.

You can look for obvious cracks yourself. Look for coolant staining behind valves, large obvious cracks, and hairlines around exhaust valves, especially between the center 2 cylinders. Also look on the deck around the coolant passages and around the combustion chamber. Best way though is to take it to a shop and let them do it, that way you KNOW there aren't any you can't see.

Re: Head gasket seems ok, but coolant was bubbling...Why?
 

Usually if you have a blown HG that is venting to the coolant, you will have an ultra clean piston compared to the others. When the piston is drawing in air, it will usually get a little coolant in with it. When it combusts you get a steam claning effect, and the high pressure in the cylinder will then vent some gasses to the coolant system.

My guess is that what you were seeing is some steam bubbles.

If you overheated even once and you have the heads off, GET THEM MILLED. :alert: I made the mistake of not doing it, and the heads would not seal, they would seep some coolant under boost. I then rebuilt the motor and had them checked, and the machine shop took off .006 off to make them flat again.

Re: Head gasket seems ok, but coolant was bubbling...Why?
 

Thanks again.

I didn't see any super clean pistons, valves, etc...but I think I'll err on the side of caution and have them checked anyway.

For 40 bucks, it's money well spent.