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2004 chevy trailblazer_lt
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Discussion Starter · #1 ·
Hi guys,
There have been many threads about cracked exhaust manifolds and lots of information and advice about how to replace them. I'm currently mid process, and wanted to share my experience and hopefully someone will benefit from it.

In the spring in New Brunswick, Canada there is a lot of flooding and sometimes there is 12-18 inches of water across the road. I think this is where my problem originated, by going through the flood waters a little too fast and splashing the manifold. The first noise that I heard was a low tick in the engine, and only under power. Eventually (over 6 weeks) the noise got louder...it sounded like an old truck that needed a serious tune-up...and the truck began to lose power. My highway cruising speeds began to get lower when towing...and you just know when you are not running at peak power.

I popped the hood and listened for the ticking, but it was hard to hear unless under load....reving helped a bit and I was able to tell where it was coming from....the exhaust manifold. Since parts are more expensive in Canada, I wanted to make sure that was it before ordering, so I removed the three nuts on the heat shield and took it off. Sure enough, there was a small hole smiling back at me about 3mm long and 1mm wide. I now knew the truck was going to be parked until I replaced it.

I bought some Gunk Penetrating Oil and soaked the 11 manifold studs and three downpipe nuts three times that evening, about two hours between applications. It gave me an excuse to sneak off to the garage and have a beer. The following morning, I put another spray on and then in the early evening I was ready to take them out. I read alot about people snapping the bolts, so I started with the ones that were clearly visible in case I messed up. I put the ratchet on, and made sure the socket was square on the bolts. I tightened it first, then loosened, then tightened, then loosened, then tightened, then pop....it came out. Some of the studs popped when it broke free, but I still worked it back and forth just to be sure.....you need to be extremely patient. I continued with the other bolts that were clearly visible, since I wanted to make sure that my technique was going to work again, and that it wasn't just a fluke. It worked....so I continued all the way to the front, and then made my way to the back and all eleven came out without issue.

I then needed to tackle the three cat nuts on the downpipe. Even though they were well soaked with penetrating oil, there was no moving them. I needed heat...and lots of it. I've got a plumbers torch with a push button flame, so I was able to get it on the nut, then click it on for the heat. I was able to heat two of the nuts by going in through the wheel well and I would heat it up until it was cherry red. I then put the closed end of the wrench on and snap them free. The third nut was harder to get at, but you can get a torch on it from underneath. Once cherry red, the third nut came off with an electric impact and three extensions.

So....the job is almost done...all of the studs/nuts are off, but there isn't much wiggle room to get the manifold out. I'll need to remove a couple more parts to give more room, but I expect it'll be out tonight. I'll be sure to share my progress....and thanks to everyone that provided such great advice.

Jeremy
 

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2003 chevy trailblazer_ls
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5,268 Posts
that reminds me not to drive thru any sudden puddles of water that may form during any rainy season here in CA...
 

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2004 chevy trailblazer_lt
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9 Posts
Discussion Starter · #4 ·
I finished up the job last night...here's what I encountered.

The O2 sensor was completely stuck...so I put it on my bench vice and torched the manifold until it was cherry red. Remember....you aren't going to burn anything, and the hotter it is, the easier it comes out. A little help from my pipe wrench and a five foot bar and it came out effortlessly. After it cooled, I cleaned the threads and reinstalled it into the manifold.

The hardest part about the reinstall of the exhaust manifold is the torqing and the need to do it three times. I've seen people on here indicate 15ft/lbs, but I followed the specs that came with the manifold, which indicated 17ft/lbs. The first pass was the hardest, the second pass, all but two took more turns and on the final pass, it was only two that took more turns. So it's very important to do three passes.

Everything else went back together very easily....the hardest part of the job is getting it unbolted without breaking the bolts.

I took it for a test run, now I can hear all of the other noises that will require my attention. Overall, I was a medium difficulty for a backyard mechanic, just because of the patience needed.

Cheers...and thanks to all those that have given details in the past.

Jeremy
 

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2003 chevy trailblazer_ls
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do you live in an area with alot of salt on the roads?

When I replaced my O2 sensor it came out with ease. I actually had more trouble unclipping the sensors connector than I did unscrewing the sensor...
and this was done at about 130,000.

I live in so cal- no salt here.
 

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2004 chevy trailblazer_lt
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Discussion Starter · #6 ·
Yep...definitely lots of salt here in New Brunswick. The truck I bought came from Boston and I've had it for about a year and a half...so, it's pretty clean compared to other TBs around here.
 
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