Good discussion, Matt!

Failure into the coolant passages (instead of, say, into the dead space between the coolant passages on the UIM) may have more to do with the fact that the cooling system exerts a mechanical force at those areas in the form of pressure. If there is no coolant in those passages, we have gas under 15 pounds of pressure looking for a way to get out. Knowing how easy it is to trap air in these engines, and knowing the location of these passages in the system, it is easy to imagine how the perforations occur where they do.

The stovepipe is deeply embedded in an enclosed space. The air being pulled in through the throttle body is cold compared to the temperature of the stovepipe. And while there may be some mixing and turbulence at the top of the stovepipe, it is easier to imagine a partial vacuum, or slow moving air around the base of the pipe, neither of which provide for the conductive heat transfer of heated air from a 1000F gun. This has made me wonder if the highest heat conditions and the most damage occur on a hot shutdown, where the pipe may be hot, but the cooling air flow is suddenly gone.

My suspicion is that if the temperature of the composite could be held at the temperature of the coolant, and if coolant were continuously present in the passages, that few if any, failures would occur.

Finally, let me say that at this point in time, I honestly believe we have this problem solved, so there is little incentive for additional research. Now, if we see sleeve and small pipe systems failing in the future, it may be worthwhile to go back and revisit some of these interesting questions.

I would have liked to have been party to the discussions and research at GM when they found the first failures in this poor design.

Me too, me too.

Given the lack of data, I think we'll have to leave this lie where it is, but it'* been a good chat - if I have some spare time and money, I might look in to it some day, but probably not. The increased air gap (and physical barrier) should protect these engines longer than we really need to care about

IF it helps at all a motor recently swapped at my house had it'* TB pulled off and I looked at that EGR bore for a long time. It looks good w/o pulling the motor. It'* not coked up and cruddy. The car was a 2000 with 200,000 miles on the clock and the intake was dated early 2000.

ok guys, got some really really bad news here. My buddy swapped the intake out with a bone yard one (he works at this one) we changed the gaskets, torqued all the good stuff down, time to fire it up right? wrong!! I replaced the coolant elbow, it has a slow leak, and also, when i tried to start the car up, gas started pouring outta those vacuum lines that run to the throttle body :( D*mn it!! this car is really screwing me

There is a good chance that the gasoline from the vacuum line is from a bad fuel pressure regulator. The leaking coolant elbow may be from a bad o-ring or a corroded or just dirty bore in the LIM or the tensioner assembly. You could try to carefully clean the bore where the o-rings for the coolant elbow sit with a toothbrush-size wire brush followed by steel wool and finally brake parts cleaner. If the surface looks good, you should only need to put some silicone grease on the o-rings to prevent tearing them when you install them. If you find pits in the metal where the o-rings sit, you might be able to seal them with RTV silicone. Try to first fill any pits that you find, then put a light coating of silicone seal on the o-rings before you install the elbow.

Prior to these repairs, did you have an internal coolant leak? If so, have you changed the oil? And have you read the Techinfo articles linked for you?

i bought the new by pass hose and installed it when i put the new lower gaskets on. I dont really believe i had a lower intake leak. The car is actually doing the same thing it did before when it actually left me straded. When i turn the key, nothing outta the ordinary. But when i try to start the car, all the vacuum lines start leaking coolant I dont know what to do. The car acts flooded nearly. Do I have to remove the lower manifold for the coolant elbow?? I did check on all the links, (thank you all for sending them) sorry, all the vacuum lines start leaking gasoline

As Bill mentioned, the fuel in the vacuum lines could be a bad fuel pressure regulator. Pull the vacuum line off it, and see if the is fuel in it. If so, replace it, and don't try to start the car until you do. If it backfires, you'll have an explosion that will blow apart your upper, and probably start a fire.

If you remove the tensioner, you can replace/repair the elbow that way, instead of taking off the LIM again.

Well, there'* the obvious question - why was the car at the 'yard? It'* very possible you grabbed an intake that has failed. On many failures, you can't see a passage at all - you need to probe (pick) at it with something sharp - if the nylon starts breaking away, you've got a bad intake.

The plenum i got from the bone yard came off a wrecked 2000+ 3.8 that had low mileage on it. So hopefully, thats not the case. I took a poke stab and poked the inside walls and it was solid so i should be good there. The gaskets were all new, replaced the uppers and lowers with the TB as well, so right now i think the whole gas leaking outta these vacuum lines is whats killing me. The gas is coming outta the little circular thing on the top of the fuel rail. Thats the fpr right? Can i switch it out or do i need to replace the whole rail?

You can just replace the FPR. If you look at it, you'll see a snap ring that holds in it, and has to be removed.