First I want to apologize for my poor English. It´s not my native tongue since I'm from Sweden.
One day in late June when cruising around a white cloud suddenly came out from the left exhaust pipe. Stopped the car. Tried to start it again and a white cloud came out again but after like 2 minutes it disappeared. Drove the car back home (10 minutes). Day after I checked coolant water level and it was empty. Then I checked the oil pan. It was full of water.
Broken head gasket was my first suspicion. Took the car to the workshop. They took the heads off. Gasket not broken. Heads looked OK. Water in cylinder 4. No visual cracks in engine block (not easy to check though)
Couldn't find any issue. Heads pressure tested with no remark. Decided to change gaskets, milled the heads (or whatever it´s called) and put the engine together again since we couldn't find any other issue.
Engine started as usual but after 10 minutes drive low coolant lamp started lighted up. Stopped the car and checked coolant water level. It was empty. Filled up and started again. After 10 minutes the lamp was lighted again. Went back to the workshop. Day after oil pan was full of water again.
Don't have any more ideas. Hope that someone in this forum have some ideas..... Kind of desperate now.
If not, I will dump the price and sell it as is or tear it apart and sell parts.
So please, if you have any proposals what it can be except cracked engine block let me know.

It´s a 1993 C4.

 

It would be a good idea to say what year Corvette you have as there are several possible engines you could be talking about, each with their own unique quirks.

 

Right! It´s a 1993.

 

Seems like it must be coming in from: gasket, head or cylinder wall...

 

Tossing this in just for my$.02 worth. The intake crossed my mind cuz the coolant flows through there on most of these guys but getting water in #4 from there seems to be a stretch. Hate to say it but... doesn't sound good.

 

The OP stated he has a '93- so it is an LT1 engine.
As I recall, the LT1 intakes manifolds do not have any coolant passages.
Now the throttle body does have coolant going though it, however the line to it is pretty small.

 

Put air pressure in the number 4 cylinder as if you were using air pressure to keep valves up to change valve springs. If you lose pressure you have confirmed there is a leak in that cylinder. If you can not find a leak in the head gasket it seems there is a crack in the cylinder wall.
With a bore scope inserted into the cylinder via spark plug hole, pressurize the cooling system with air and see if you can spot a leak in the cylinder wall. With the system pressurized you should see coolant seeping from wherever it is coming from.

Has the engine been rebuilt with boring of the cylinders or is it still the original bore size?