Mechanics

CHEVY UPPER INTAKE MANIFOLD (PLENUM) KEEPS CRAC

2001 Chevrolet Malibu

Engine Mechanical problem
2001 Chevy Malibu 6 cyl Front Wheel Drive Automatic

Hi, I am trying to reinstall my upper intake manifold, but it keeps cracking. I've replaced it 3 times already with manifolds that I've been able to find at LKQ (junk yard). It always cracks in the same place. I am going by the Haynes torque specs at 18 ft/lbs.

Could the lower intake manifold be warped? Maybe the Harbor Frieght torque wrench is to blame?

Any ideas?

Much Obliged,
Thomas


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Tomshanty
June 12, 2010.




I've never really heard of that. Those are 6 mm bolts so I would lower the torque and see what happens. Also if you have replaced the intake gaskets and they gave you new bolts there is a tsb that says these bolts shold only be torqued to 13Nm=115in lbs. For the vertical bolts and 25nm=18 ft lbs for teh diagonal bolts. But check to see if the lower is warped or square. It may be your problem especially with 3 uppers replaced.

Hmac300
Jun 15, 2010.
Thank you for responding. I'm aware of the TSB for installing a new lower intake manifold gasket and used the new bolts and updated torque sequence. I should have also mentioned that I replaced the head gaskets and had the heads machined. Haynes says, " If the heads are resurfaced, the intake manifold flanges may also require machining.&Quot; I mentioned this to the machine shop and they said they don't take that much off to require that. I'm starting to think otherwise. Could this be my problem? Thanks again.

-thomas-

Tiny
Tomshanty
Jun 19, 2010.
I would think it would. Especially since having the heads shaved. If they were taken down.010" that could do it because teh aluminum heads move around so much from heating and cooling. Now what you might do which I forgot about is put two sets of gaskets between the upper and lowr manifold to make up the difference. That would be a cheaper fix and might just work. It would be worth a try anyhow.
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Hmac300
Jun 20, 2010.
I'm gonna give it a shot and use 2 plenum gaskets. In my head, it makes sense for why this would fix my problem, but i'm not getting my hopes up. I'm thinking worst case scenario I'm going to have to remove the lower intake and have it resurfaced. If this is the case, will I still be able to use the lower gasket? This is not something I want to buy twice for 90 bucks. Thanks again for your help and for not giving up on me.

Tiny
Tomshanty
Jun 21, 2010.
I'm not sure what type of gaskets you have on your car so I really can't say. If they are the newer style and are rubber, as long as you see if the rubber isn't broken loose I would think you could reuse them. If you do get the lower resurfaced, ask the guy who did the heads on how much he took off. You don't want to take off more than he did you would want to take off the same amount to keep thing correct.

Hmac300
Jun 21, 2010.
Just out of curiousity, if I were to use the cracked intake plenum, what's the worse that could happen? The crack isn't all the way through to the other side.

Tiny
Tomshanty
Jun 28, 2010.
If you got it welded up I imagine that the worse that will happen is a vacuum leak and the computer may take care of that but your gas mileage would suck. But you could get it welded up and it may even strengthen it.

Hmac300
Jun 29, 2010.

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