JCL what sort of tests could the OP ask for of his shop? What's the list? Can he ask for numbers/written report on a leak down test or any other appropriate test? I drove it around, to me is not a test. Am I wrong?

If this were mine I would want to know that list and approach the shop or my own diagnosis, and say here are the tests I want you to run. Please give me written reports of your results.

So far the OP hasn't convinced me that conclusive test results were given to determine that the engine needs rebuilt or replacing.

OP all those codes may be the minor fixes that will make your engine good again, maybe not/ I'd be spending a few hundred on tests before I just capitulated to a $6000 plus repair.

The problem is that we don't know what the shop tested, just what their apparent conclusion was. We have partial information and some of it seems to conflict. So we have all this random internet diagnosis going on, and it is very unlikely to help the OP, IMO.

Troubleshooting is a methodical, step by step process. This thread is the opposite of that, with lots of random suggestions.

Time to go back to basics.

1) Is there a coolant leak? Has there been a leakdown test?

2) What is meant by 'pressure in the system'? Pressure from the rad cap? Pressure from combustion pressure leaking into the water?

3) 'Engine is toast' means nothing without knowing the why. But it suggests block or head damage, possibly a leak between one of more of the combustion/oil/coolant circuits. Something caused multiple shops to conclude that the engine was toast They could all be shysters, or we could be missing some key piece of the puzzle that is causing all this guessing and accusations of them being shysters. Could be something as simple as bubbles appearing in the coolant from a crack.

4) Is the thermostat operating correctly?

5) Is the water pump operating correctly?

The OP appears to require a shop to do the repairs. If so, then that shop also has to agree with the diagnosis. It is expensive to tell a shop how to do the diagnosis, it is better to let them do it and have them explain their conclusion (or suspicion, if they can't conclude for sure what it is). This assumes the shop is competent, and that the OP trusts them. If not, time to find another shop.

Well put JCL.

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Heres a starting point hopefully that can help:
Car acting normal and driving ok. Pressed a/c button and turned down temp while in a drive-thru. Within under a minute, temp gauge shot over almost instantly, and steam came from under hood. immediately pulled car to the side and shut off. turned on 5 min later, temp gauge in the middle, car acting fine. Drove directly to the first mechanics shop, which luckily was only three lights away. by the third light, temp started to bobble towards the right a bit. didn't hit red. got to the shop, left it with them for the day. they said, need a new radiator. asked if it was drive-able for a couple days, because I had meetings to attend to that could wait (Senior at the Univ. of Miami). He said yes, just add water to the rad. I did so.

Time for new rad to be put in. Had it towed, just to avoid any possible overheating. car started and drove onto flat bad 100% fine.
get a call later saying they put the new rad in, drove it around the block, it overheated again. Was told there is now smoke coming from the exhaust, have yellow goop under oil cap. Told that the engine was done, and I need a new one.

With the 3rd shop I had it taken to, they said as a final diagnosis that there is compression in the cooling system. He was very stumped as well, said it was very weird. Couldn't give me an exact reason. He also said there was loss in compression in all cylinders.... which I don't get.
Said possibly, that when I had my #6 piston replaced (DISA valve broke, flew into cyl. 6, etc etc), that they might have either not torqued the head bolts down enough, or might have overtorqued them and stripped them, and the engine couldn't handle the stress from the long drive from new york.

However the car wont start what so ever. won't even crank or try to turn over. Seems like an electrical problem of some sort. Lights flicker, interior lights are very weak, the lock-beep is faint. Is it possible at all that during the course of things steaming and spraying, the alternator might have been effected?

Allstardt, Sorry you are having such a bad go of it. I am ready to throw in the towel on this engine. Regardless of the other symptoms you are still getting coolant in your oil. could be coming from a broken head or a broken block or something else that would render the engine toast.

I would shop the junk yards locally and online to find a used engine or a rebuilt one depending on the prices, mileage etc. Get one of your indies to install it. I shopped rebuilt engines a few months ago They have 4 to 5 yr warranties and come in between $2700 to $3500 for a 3.0. Used can be had for around $2000 plus shipping. probly $2000 to install.
If you like the car and the rest is in good shape... its decision time.

sounds to me like cylinder pressure is leaking into the cooling system, possibly blown head gasket , cracked head, cracked block.

you already got the cooling system pressure tested, so next i would have the cylinders pressure tested see what the cranking pressures are and that they are all equal.

based on the outcome of this and especially if 1 or 2 are low i would be removing the head for a visual and then crack testing.

if the motor starts and runs fine with a good idle and normal power it can not be to big a problem

BigWave, That's good advice if the OP can take it apart and test it himself or take the head and the block to a machine shop. If he can't do the work himself then, the labor to diagnose is going to dig the hole deeper.

4 mechanics say the engine is done. I translate that to mean that the cost to diagnose, Test and repair (what if you spend that money on diagnosis and the engine is found to be irreparable) the existing engine exceeds the cost of swapping out for a rebuilt engine with a 4 or 5 yr warranty, labor considered.

I would tackle a tear down because I would do the work and I would learn something new, but not everyone is like me.

blue juice
 

napa sells a kit to tell if co2 is coming out the cooling system its seals the over flow tank and You pass the air off the coolant and it changes color I would try that ?