2 Donuts and a leak

[BIG BLUE]

no it's not a "pit" stop on a road trip, it's the latest in the "monthly" fix-it log for the wife's Sub.  Ok guys, here is the cliff note version;

 

97 K1500 Sub. Had the whole converter/crossover assy replaced last spring (17K miles ago). Replaced both donut gaskets at the ex/manifold, and flange gasket after the cat at the same time. Well yesterday the wife goes on a 3hr trip and returns to let me know the truck is "loud again". WTF, now what, so I crawl under and with the truck running I feel exhaust coming from where the crossover head pipe bolts to the ex/manifold.

 

Must be the donut gasket is bad again, so I take it back to the muffler place and they tighten the 3 bolts and say there is still a bit of a leak so go get the "dealer only" part and they'll replace. Next stop, GM parts were buddy works and pick up 2 new donut gaskets (ceramic in design and too brittle if you ask me). Also pick up a new starter for the Sub since that will be this weekends project too. Anyway, return to the muffler shop and have them replace both donuts to the tune of $40 total.

 

I pull out and accelerate to hear just about the same exhaust sound as when I brought the thing in in the first place. Disgusted, and running late for work, I stop and get gas and pop the hood, well NOW it seems to be coming from the passenger side (driver's side when I took it in was leaking) So, I gracefully SLAM the hood and proceed to work.

 

One thing the guy at the muffler shop mentioned was that if the new gaskets are installed and the sound is still there, it could possibly be a warped exhaust manifold. Not sure if he means where it bolts up to the block, but assume where the pipe meets the crossover and the donut does not seat properly. Anyone with any ideas would be helpful. I'm tempted to try and "tighten" the bolts another 1/2 turn or so but realize stripping is a worry. Oh well, looks like the weekend is already filling up with this and the starter replacement job.

 

Venting,

BIG BLUE

 

P.S. Even "cliff" get's long winded sometimes ;)

[01z71]

Wow, Big Blue sounds like you gotta busy weekend coming up.  Sorry to hear about your problems.  If it was me I would try tightening the bolts another half turn or so (carefully) and see if the exhaust leak goes away.

 

Best of luck.

[95Yukon]

Mine were of the softer material from the factory. The hard ones won't seal as well if there are any clearances from a slight warpage, but the softer ones should. I would replace them both with the ones that have a bit of a softer sealing lip, and use a light coating of permatex ultra copper on all the surfaces. The ultra copper is sensor safe and will help keep leaks from developing. Also, have them "double nut" the studs if they are loosening up at all.