cracked exhaust manifold

[BeenBlazin]

im in the process of replacing my cracked exhaust manifold and wanted to replace the bolts also. does anyone know what grade these bolts are? i was just gonna get new bolts from my parts house instead of the GM ones

 

[jbones]

Do you meet the criteria for free replacement from GM, for thier cracked manifold issue?

 

[BeenBlazin]

i doubt it. its an 04 trailblazer. i already have the manifold. a few of the bolts were broken so im deffinately gonna replace all of them.

 

[DJones]

I would recommend the GM bolts because they are all ready to go with threadlocker. Good luck getting the broken bolts out.

 

[BeenBlazin]

ya your right ill just order the bolts from GM next week. that way i can have the weekend off. good thinkin haha

 

[jbones]

i doubt it. its an 04 trailblazer. i already have the manifold. a few of the bolts were broken so im deffinately gonna replace all of them.

I dont' remember the years the GM letter applied to but I do recall the mileage was under 120,000 for free replacement. Had my "08' replaced for the cracked manifold (free of charage) at the dealership a few months back.

 

[BeenBlazin]

well thats too bad i would have just missed it im at 141000 miles. are they also fixing the broken bolts for free?

 

[coleman]

I think I have a cracked manifold as well. A couple months ago, I've noticed a very strong exhaust odor in the cab, normally when the engine is started and it's cold. Otherwise, I don't really notice it at all. If there is a crack, then perhaps it's sealing itself after the the engine heats up, and opens up more when the engine cools.

From what I've read, it doesn't look like a simple, DYI job. Best to take it to the shop?

What do you guys think?

Thanks.

 

[BeenBlazin]

doing the exhaust manifold swap isnt hard. the hard part is that usually a few of the bolts break off and have to be removed. then it turns into a real pain. some people drill the bolts and use an easy out. i started welding nuts to the broken bolts to back them out but ran out of welding gas. i already knew the tank was almost empty. when you remove the bolts you want to back them out about 1/4 turn then back in 1/8 then out another 1/4 turn and back in 1/8 and so on. its the high temp thread lock on the bolts that causes the problem.

 

[coleman]

doing the exhaust manifold swap isnt hard. the hard part is that usually a few of the bolts break off and have to be removed. then it turns into a real pain. some people drill the bolts and use an easy out. i started welding nuts to the broken bolts to back them out but ran out of welding gas. i already knew the tank was almost empty. when you remove the bolts you want to back them out about 1/4 turn then back in 1/8 then out another 1/4 turn and back in 1/8 and so on. its the high temp thread lock on the bolts that causes the problem.

You've convinced me. To the shop it goes. That kind of aggravation I don't need.

 

[BeenBlazin]

ya it is a deffinate pain in the ass just be prepared iv heard of a few situations where the bill got pretty high depending on how many bolts break. GM removes the cylinder head and charges i think over a couple of grand. what ever shop you bring it to make sure you discuss the chances of broken bolts and price beforehand so you dont get a big suprise. if you remove the heat shield from the exhaust manifold you can usually see where its cracked. theres lots of cases where people get some high temp furnace cement to patch the crack and theyve had success. in my case the crack ran down the outside and back up the inside so the manifold was pretty much cracked in half. im not trying to scare you just giving you a heads up. some people get it off without breaking any bolts at all. i have 3 broken bolts

 

[coleman]

ya it is a deffinate pain in the ass just be prepared iv heard of a few situations where the bill got pretty high depending on how many bolts break. GM removes the cylinder head and charges i think over a couple of grand. what ever shop you bring it to make sure you discuss the chances of broken bolts and price beforehand so you dont get a big suprise. if you remove the heat shield from the exhaust manifold you can usually see where its cracked. theres lots of cases where people get some high temp furnace cement to patch the crack and theyve had success. in my case the crack ran down the outside and back up the inside so the manifold was pretty much cracked in half. im not trying to scare you just giving you a heads up. some people get it off without breaking any bolts at all. i have 3 broken bolts

Wow. Thanks for the advice. If it comes to that, I'd have to make a serious decision about whether or not to keep the truck. I'm trying to hold off long enough to maybe get the new Trailblazer if it comes out in a couple years. I'll call my shop tomorrow to see how much they want.

 

[Sparky]

I'll probably have to deal with this issue at some point. Last I checked mine wasn't cracked, but I do think I have a busted off bolt already because it sounds like it may have a manifold leak at cold startup in the morning.

How much work is it to pull the head and just have the shop extract the bolts from the head only? I can't imagine it would be fun, but maybe for someone who is more mechanically inclined (or just simply crazy ) that might be a cheaper option.

 

[BeenBlazin]

well theres a bit of room to work with when the manifold is out. i also removed the air intake box and the windshield washer resevoir and the upper rad hose that goes to just behind the power steering pump. its at the very back where things get pretty tight. my trailblazer is torn appart at work ill try to take a pic tomorrow to give a better idea.

 

[MichEnvoyGuy]

I'll probably have to deal with this issue at some point. Last I checked mine wasn't cracked, but I do think I have a busted off bolt already because it sounds like it may have a manifold leak at cold startup in the morning.

How much work is it to pull the head and just have the shop extract the bolts from the head only? I can't imagine it would be fun, but maybe for someone who is more mechanically inclined (or just simply crazy ) that might be a cheaper option.

Keep it simple. I had the same problem at cold startup. 3 or 4 of my manifold bolts were loose, very loose. Tightened them up 2 years ago, havent had a problem since Btw, (Knocking on wood!) no cracks in my manifold at 152,900 miles!

 

[Sparky]

Hmm maybe I should check that. I just figured with all the bolts that are seized and break that there would be no way for them to just simply be loose.

 

[MichEnvoyGuy]

Hmm maybe I should check that. I just figured with all the bolts that are seized and break that there would be no way for them to just simply be loose.

Well, I was very much like you a few years ago and was over on the os searching high and low for how-to on the exh. manifold replacement because after all of the problems I read, I was sure I had a cracked manifold or sheared off bolts in the head. A few other members said their bolts were just loose. I took of my heat shield, fully inspected the manifold and to my surprise there werent any cracks at all! Looked at the bolts, check, they are all there. I could see black carbon at the front of the manifold/head. I put a socket on the bolt and it was so loose I could've turned it a few times and taken it out by hand!
I tightened 3 or 4 bolts that were as loose. The sound difference is amazing. No more cold start up exhaust leak sound coming from the engine. Heck, it even sounded different at cruising speeds, a lot quieter. Check your bolts first, for sure

 

[coleman]

Well, I was very much like you a few years ago and was over on the os searching high and low for how-to on the exh. manifold replacement because after all of the problems I read, I was sure I had a cracked manifold or sheared off bolts in the head. A few other members said their bolts were just loose. I took of my heat shield, fully inspected the manifold and to my surprise there werent any cracks at all! Looked at the bolts, check, they are all there. I could see black carbon at the front of the manifold/head. I put a socket on the bolt and it was so loose I could've turned it a few times and taken it out by hand!
I tightened 3 or 4 bolts that were as loose. The sound difference is amazing. No more cold start up exhaust leak sound coming from the engine. Heck, it even sounded different at cruising speeds, a lot quieter. Check your bolts first, for sure

I'm really going to have to take a look at this. The last two mornings there was no smell. Crazy. I took a look at the heat shield and two of the four nuts that hold it on are missing. No rattling from that, so that's good. I guess it just makes it easier to take it off to check for loose bolts on the manifold. Hopefully, I didn't lose any under there if that's the case. Will try to find time to do this tonight after the engine cools off a bit. Might need to wait for Saturday morning.

 

[Sparky]

Actually part of me doesn't mind the initial startup exhaust leak, on a cold start it almost sound diesel-ish But I can't imagine a consistent exhaust leak is doing me any good. Could affect mpg a tad bit after all if it messes with the O2 sensor reading.

 

[BeenBlazin]

maybe GM wasnt using their high temp thread lock on the 02 models?

 

[jbones]

Found it, had my cracked manifold replaced under this letter at around 50,000 miles.

View attachment 19037

 

[MichEnvoyGuy]

I went out to the garage earlier out of boredom and decided to check my exhaust manifold bolts. The last time I checked them, back around 2008 or so, the front 4 were so loose, I could see the exhaust manifold move closer to the block as I tightened them!! I could tighten them with my fingers on the socket (no rachet).

Tonight, 4 years later - same thing!

I had been hearing exhaust noise lately but didnt really want to bother with it until it became a problem. Well, my fuel trims were elevated to the rich side. If air is leaking IN to the exhaust stream, it will skew the O2 data in the exhaust manifold into thinking its a lean mixture, thus having the PCM richen the mixture, thus throwing off your PCM fuel tables and killing your mpg's!

My point: Check your exhaust manifold bolts. Its easy, they're 13mm, and Im willing to bet dollars to donuts that if you've got exhaust noise and dont have a cracked manifold, they're loose!

 

[Sparky]

Something to add to my "to do" list. Thursday looks to be a decent day, so maybe that evening after work.

 

[BeenBlazin]

well thats good the bolts were loose and the manifold wasnt cracked. i ended up getting my broken bolts out and installing my new manifold and what a difference. i cant tell that the truck is even running. it was so loud before and i guess i just got used to it. i used to notice how horrible my mileage was and since getting the new manifold on it seems to have majorly improved.

 

[coleman]

Okay, I took off the two remaining nuts on the heat shield and the nut holding the transmission dipstick in place, but how the heck do you get the heat shield away far enough to really check out the manifold??? I did stick my fingers in there a bit and, of the bolts I could touch, I felt that one was loose, so that could be the problem, but I can't get the heat shield away from the manifold enough to tighten it.

I guess the O2 sensor has to come out, but is it okay to take that off with an open ended wrench? I read somewhere else that you need a special tool for that.

 

[coleman]

I tightened up the only bolt that appeared loose, which was the only bold that was darkened by exhaust. Still haven't been able to remove the blasted heat shield. The thing that concerns me now is, when I feel around to the bolt closest to the firewall, I don't feel one. It feels as though the head of the bolt broke off. I can feel a circle within a circle. Lord knows I can't see it. It's behind that wrapped pipe in the back. Grrrrr!!

Ideas?

 

[BeenBlazin]

ya that heat shield is always in the way. the 02 is usually in there pretty tight having the engine warm helps loosen it up a bit. there is a special wrench for it its a boxed end wrench with a small cut out for the wire to pass through but usually an open end wrench will work just dont round off the sensor. if you follow the wire from the sensor to behind the power steering pump you can unplug it to remove the heat shield without removing the sensor. that back bolt is a common problem too. kind of a mystery to me. the head of the bolt was missing from mine too but when i did my swap what was left of that bolt came out easily. on the sensor plug theres a little pin that needs to be pulled out first and then put a little pressure with your thumb to release the clip. when you look at it youl know what in talking about. dont just pry the clip up like a mad man because the retainer might break. just be gentle its easy. i drove around for about 6 months without my heat shield because i didnt have time to get around to doin the swap.

 

[coleman]

Thanks for confirming the missing bolt head. That one three me for a loop.

The big problem with mine is that the bracket that holds the oil dipstick and an AC pipe going to the compressor is in the way. After I took the first nut off on the pipe bracket, I couldn't move the bracket enough to get it off the bolt to get at the nut underneath that that holds the dipstick. If I could get those off, I would be in much better shape.

In any event, I did tighten the one loose bolt and I didn't smell anything the two times I started it up since,
though sometimes I don't smell it anyway. Maybe I tightened it up enough to solve the problem. We shall see.

 

[BeenBlazin]

i think you just have to bend that bracket a little bit to get it out of the way. i know moving that stuff is a PITA they make it so it fits in 1 spot only. the second nut is part of the stud. if you back it out it will also remove the stud wich may help you get that stuff out of the way. its easy to get it back in so dont worry about it. now i didnt remove the dip stick i just kind of turned in counter clockwise and it swiveled out of the way. but just dont pull on it as you turn it so it doesnt pop out. hopefully tightening your bolts will cure your problem. mine wasnt leaking from the back bolt with the broken head.

 

[MichEnvoyGuy]

Each time Ive tightened my manifold bolts, Ive never been able to get the heat shield out of the way fully. I just use either a deep well socket, or a short socket with a small extension. Even a swivel might help get in there. Im able to access all of the bolts that way.

And dont panic about the 1 bolt missing - it might not have broken off (it very well could have but lets look at the positive first!) maybe it just loosened and fell out. The reason I say this is mine get so loose that if you loosened it another 1/2 turn, it would come right out. Had I not caught it in time, Im sure I'd have lost that bolt on the road somewhere.

If you cannot see if there is a broken bolt stud because of the hard to get at location, try to stick a bolt in the hole. Easy way to find out first.

 

[coleman]

Yeah, I had to use a swivel and an extension. The bolt is definitely in there. I could feel it with my finger and could tell that it was rusty. Must have been that way for quite some time. Hopefully the one I hit did the trick.

 

[MichEnvoyGuy]

Yeah, I had to use a swivel and an extension. The bolt is definitely in there. I could feel it with my finger and could tell that it was rusty. Must have been that way for quite some time. Hopefully the one I hit did the trick.

Just curious, how tight did you crank the bolts?

I was afraid of breaking them so I snugged them up real good but not gorilla tight. My logic says that I'd rather re-tighten them in a year vs. have to take everything apart (and risk more broken bolts) when I break one by over tightening it.

 

[coleman]

Just curious, how tight did you crank the bolts?

I was afraid of breaking them so I snugged them up real good but not gorilla tight. My logic says that I'd rather re-tighten them in a year vs. have to take everything apart (and risk more broken bolts) when I break one by over tightening it.

Snug, plus a little, plus a little. I was careful not to go crazy. With the swivel, the extension, and the swivel wrench driving it, it would have required some effort to get it super tight. Like you, I'd rather do it again later on than break it stupidly.

 

[jballentine]

I am going to check mine tomorrow. I just started currently getting a noise from starting from a stopping position and when I turn the TV on and off I can hear it. Sounded like I had a hole in the pipe somewhere then when I had my wife in the TV with me she said and I could hear it and we both felt it after it cranked over something bounce off the passenger floor board. Maybe it could be a motor mount but I had her rev it a little bit while I watched the engine I did not really see much movement. It has been pretty cool in temp here and I was looking under the TV while running but did not see any visible exhaust. I am just kinda dumbfounded over the noise right now I hope this is the issue.

 

[coleman]

Unfortunately, the problem persists. Looks like I'm going to have to bring it in after all. I suppose there could be hairline crack. I don't actually hear anything that would point to a crack, though. Maybe you'd only hear it if the crack were sizable.

Is there a gasket between the manifold and exhaust pipe? I wonder if that could be the problem.

 

[BeenBlazin]

yes its a led donut. theres 3 studs and nuts that hold your down pipe to the exhaust manifold. are you just smelling exhaust? there could be a leak from several places. are your pipes rusted out? how about your catalytic converter?

 

[coleman]

yes its a led donut. theres 3 studs and nuts that hold your down pipe to the exhaust manifold. are you just smelling exhaust? there could be a leak from several places. are your pipes rusted out? how about your catalytic converter?

Yep, still smelling it, but only on startup, or at least that's when I notice it. I'll have to drop it off with the mechanic. Time over here is in short supply and I don't want to take a chance with any exhaust coming in with my little one in the back.

 

[BeenBlazin]

ya i hear ya thats not a chance i like to take either. let us know what your mechanic comes up with.

 

[Sparky]

My heat shield comes right out, not sure what your problems are... But then, the lower half of mine is rusted away

 

[coleman]

Update: I finally got it to the shop. Turns out I had a couple of broken bolts and a bad gasket. Replaced the whole thing, plus the O2 sensor that they were unable to unscrew, even with applying heat.

Now, no smell whatsoever. In the past when I stopped behind other cars, I thought I was smelling their exhaust. Turns out it was my own exhaust pooling under the hood and leaking in. This has been going on for more than a year. I wonder how many brain cells I've lost.