Im looking for some advice on a bad coolant leak that Ive got on my brothers Jimmy.

Lets start with whats happening. I just did the intake manifold gaskets on this engine, I had it running for a few minutes with the radiator cap off so it could bleed out the air in the system, after it was full it ran for a bit longer and started to overheat, I figured no big deal there must be some air still in the system not letting it flow right. It was low on coolant, but I noticed there was a puddle under the muffler, I thought maybe there was still some liquid in the exhaust from before the gasket change, but after running it for a while more and checking the oil, I can tell that coolant is definitely mixing with the oil, the oil on the dipstick is like a milkshake, and the coolant level keeps going down.

OK sorry for the long story, but here is the point and my question to anyone who can help, is there a way that I can definitively diagnose where the leak is, without taking the engine apart again??
Like I said, I just changed both upper and lower intake manifold gaskets, so it is possible I screwed up somehow.(the reason I changed the gaskets was because it had coolant coming up through the seal on the front drivers side between the manifold and head with no pressure in the system, just as you filled the radiator that was enough to force coolant out, so it was a major leak.) And I do know that on more than one occasion before this, my brother let the engine overheat majorly so it is possible that there is a blown head gasket, a cracked or warped head, or cracked or warped block.

Is there a way that I can find out where the leak is without pulling everything apart? Im thinking maybe a compression test on the cylinder could tell me something, but dont know if that info would even help. What do you think is the most likely suspect, did I screw up the gaskets, I dont see how I could have, but maybe there is some trick I didnt know about??? If I somehow did the torque sequence wrong maybe? I know for sure all of the bolts were torqued to the correct specs. Well thats all, any and all help is apreciated. Thanks

If the engine has seriously overheated then you'll have to check the block and heads for damage/warping. This is the likely cause of the oil/coolant mixing. No choice but to remove your recently installed intake and pull the heads off too. A compression test might help locate which bank has the damage....unless it is obvious. Good luck!

If you didn't torque the lower intake right or in the right order you may have distorted the gaskets or even warped the intake. I highly advise you NOT to run the engine in this condition water and oil don't mix at alland that how i blew the engine in my van it was also a 4.3 TBI it started with a tick then a knock and ended with a snapped crank and a connecting rod threw the block and me stranded about 30 miles from home and pissed off.

take out the spark plugs and look at them all if there is a greenish tint to the plug ans the porcelin insulator is slimy you have a blown head gasket it there are two on the same bank right next to eachother you have a blown head gasket between the cylinders