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Well, if you, an aviation guy, or me, a nuclear guy, were doing the design, no way would *we* sign off on a plastic intake manifold...I mean no damn way would this kind of crap be done on an aviation engine or a nuclear plant's emergency Diesel...
No doubt the bean counters at GM were behind this...although even BMW have built some plastic intakes...they do have the advantage of light weight and are easily made very smooth internally - still I don't like them..
^Yeah....you'd have to know in advance that it's not going to last long. You'd have to. And you'd have to at least consider that in the life of any engine it will surely overheat at least once for one reason or another.
plastic intake manifolds are hardly anything new. pop the hood on any vehicle using a 2000+ Ford Zetec or Duratec (4-cylinder, at least) and you'll likely find one. heck, i'm pretty sure the intake manifold on my 04 GTO (LS1) was plastic or at least some kind of composite. granted it all depends on the type of plastic used and the heat it sees, but if you're melting the intake manifold you have other problems.
i believe your problem is actually just a gasket. i seem to recall this being a common issue on this motor in its later years, though i may have it confused with the 3.4L.
It's not that you would be at melting temp. It's that the difference in the coefficients of thermal expansion can be different enough between the plastic/composite and the aluminum/steel cylinder heads and and engine block that it has the potential to create a serious problem. The engineers may have designed it for normal operational heat but if you get too far outside of that you could have a serious problem on your hands.
...and I'd think the intake on your LS1 is aluminum that has a black coating....
The plastic part is the upper intake, also called a plenum. The lower intake that bolts to the heads is aluminum. EGR heat is what kills the plastic. GM's bulletin says to replace both pieces with a redesigned part. On the redesign, the EGR pipe is smaller and the passage for it is larger and that stops the plastic from melting. When it melts, it opens up a coolant passage and engine vacuum draws coolant into the plenum and eventually the cylinders. Not a pretty sight. And not a cheap fix.
It's not that you would be at melting temp. It's that the difference in the coefficients of thermal expansion can be different enough between the plastic/composite and the aluminum/steel cylinder heads and and engine block that it has the potential to create a serious problem. The engineers may have designed it for normal operational heat but if you get too far outside of that you could have a serious problem on your hands.
...and I'd think the intake on your LS1 is aluminum that has a black coating....
any Cte mismatch should be alleviated by the gasket acting as a buffer. i did forget about the EGR, but in general a LOT of cars run with plastic intake manifolds and have no issue.
Mike
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