Leaking intake manifold questions - 97 Bonneville

I removed the upper intake manifold from my 97 Bonneville today to replace the leaking gasket, and I'm a little concerned about all the gunk I found under the manifold. This is the first time I've taken an
intake manifold off (I knew it would be a learning experience), so I'm not sure if what I'm seeing is normal.
I have posted a pic at http://www.thezac.com/car /
Q1: Could someone comment on the sediment? The inside of the injector holes don't look too great either.
Q2: I have read that engine damage can occur from a leaking intake manifold gasket. What kind of damage?
Q3: I heard that sometimes the intake manifold itself on these engines can get "burned out" in a certain spot - where? Is it obvious if it has?
I hope I'm not pushing my luck - I'm DIY'er whose still learning... Thanks,
Joe
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Normal. Don't waste your time trying to clean it, it will gunk up again in short order. DO clean the gasket surfaces however...

Worst case would be a connecting rod hanging out of the engine block. Spark plugs, O2 sensors and the catalytic convertors can and do suffer damage also. Pull a couple of spark plugs, if you see darkish deposits, change them out and avoid the inevitable missfire codes.

Here is a picture of the bottom of the upper plenum, throttle body end:
http://ken-co.com/zoom2.asp?Link=manifold/images/3800-6a.jpg
The larger round hole is where the EGR pipe extends up into the upper plenum, the two smaller holes are coolant passages. Here is a picture of the throttle body end of the upper plenum:
http://ken-co.com/zoom2.asp?Link=manifold/images/3800-2a.jpg
There are three oblong shaped holes visible between the two lower studs, the two outside oval holes are adjacent to the EGR hole in the first picture. The two outer oblong holes connect to the two smaller round (coolant) holes in the first picture. Probe from either to the other ( EGR to coolant passage) with a small screwdriver or awl, you'll find soft spots and/or outright holes. Gone on long enough, the whole lower part of the throttle body end around where the o-ring fits around the coolant passages will be soft and crumbly.

I always do the lower intake gaskets when I find a leaking upper, I have yet to pull one apart where the lower gaskets aren't disintegrating also. Your picture shows fluid pooled in the lower intake, I can't tell if it is oil or coolant. If you DIDN'T find raw coolant laying in the lower manifold when you removed the upper, then I'd suspect that the lower gaskets are leaking and that this is where you coolant loss is. If it is oil pooled, the lower manifold bolt threads weren't/aren't sealed. Use thread sealer/locker on the lower bolts and pay close attention to the torque specs for the UPPER plenum bolts. You HAVE to use an inch pound torque wrench because the values are quite low, otherwise you'll crush the new upper plenum. Pay close attention to the O-rings in the PCV cavity, if you forget the O-ring around the base of the PCV valve, you'll set MAP sensor codes. Watch the connections to the purge solenoid, if you reverse them, you'll set EVAP codes. Connect them exactly as shown on the underhood vacuum diagram. If you decide to do the lower intake gaskets, you'll also want to replace the plastic elbow that connects between the right side of the lower to the alternator bracket, hell, I'd do the lower just to replace this elbow since they too are a weak point and prone to failure.
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Thank you the detailed response, I really appreciate it.
Joe
On Sun, 20 Mar 2005 08:11:23 GMT, aarcuda69062

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What type of thread sealant should I use for the lower manifold bolts? The GM parts guy told me they use a silicone liquid sealant. I bought some Permatex high-temp thread sealant, but it doesn't say anything about being silicone-based. The guy at NAPA (parts store - don't know if they're national) told me I could use plummer's thread tape.
Thanks,
Joe
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joeho wrote:

You don't use a thread "sealer", you use loc-tite of some sort. Medium strength works fine.
Ian
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I dont know if its normal or not but I am sure its one of the reason why GM is in the condition its in now, I had the gasket already replaced on my 3.1. Its been a common problem for years and GM has not addressed it. 3.1, 3.4, 3.8 and I just found out yesterday that it can also be a problem on the 5.7 V8!. I had mine replaced at the dealer at about 100k miles on my 97 for about $800. Its why I dont think my next vehicle will be a GM. The problem has been going on for years with no hint of a recall.
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Essb wrote:

AFAIK, head gaskets have never really been a problem with GM engines (except for one 4 cyl engine). For head gasket problems, check Ford and Chrylser.
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He said Intake gasket not head gasket.
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"Essb" <Billy Lincoln> wrote:

Also the 4.3 and 5.0
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Oh, yours is pretty compared to mine!
http://home.cablelynx.com/~zroger73/intake/intake.html
~Roger

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zroger73 wrote:

I'll one-up ya....here's a picture of some major coolant "pooling".
http://members.shaw.ca/ianrmac/Images/3800.JPG
Ian
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