Exhaust leak?


kjmagsig

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Joined
Sep 14, 2021
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23
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Wisconsin
When I purchased this 94, I didn't test drive it much, but it sounded like it had a pretty good exhaust leak up by the engine. I figured the pipe was probably rotted out and would need to be changed up there, even though the tail pipe is almost brand new. After getting it home (the dealership trailered it to my house, they didn't think it would make the 45 minute drive.

First thing I did is get down under it and take a good look at the exhaust pipe to figure out where it was rotted. To my surprise, the whole thing is pretty much new, all the way up to the engine. So I figured the manifold was probably shot. I thought "Aha! this is a good opportunity for me to put headers on it!" So, I start looking under the intake manifold and discover it already has brand new headers on it (well, header, singular because it's a straight six.) So I thought maybe the gasket wasn't installed right or something, but I didn't tear into it right then. A couple days later I drove it to work and was surprised that, when the engine heated up, the sound of the exhaust leak went away.

Still, when I first start it up, it sounds like there is a leak right up near the engine, until it warms up, then it's just the ruble of the header. I never smell exhaust while it's warming up, it just sounds like it's leaking. Any ideas what is going on? It runs great, smooth, doesn't rev up more than normal, it's just loud until it warms up.

This is only the second vehicle I've ever had that had a header (headers,) and the first was way too loud to hear any exhaust leaks anyway (and I could look down through my floor boards and see the coffee can that was squashed onto the broken section of pipe under my feet while I was driving it. Ahh, the joys of a bondo-mobile, way back in high school... Flame orange 74 nova with street slicks on the back, black fur interior and a 7 inch snorkel hood scoop on it. Looked AWESOME from a distance...) Anyway, any ideas of why it sounds like this? Is it something I will need to look into and fix, or is it normal?
 

machoheadgames

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May 19, 2020
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Dallas, TX
When I purchased this 94, I didn't test drive it much, but it sounded like it had a pretty good exhaust leak up by the engine. I figured the pipe was probably rotted out and would need to be changed up there, even though the tail pipe is almost brand new. After getting it home (the dealership trailered it to my house, they didn't think it would make the 45 minute drive.

First thing I did is get down under it and take a good look at the exhaust pipe to figure out where it was rotted. To my surprise, the whole thing is pretty much new, all the way up to the engine. So I figured the manifold was probably shot. I thought "Aha! this is a good opportunity for me to put headers on it!" So, I start looking under the intake manifold and discover it already has brand new headers on it (well, header, singular because it's a straight six.) So I thought maybe the gasket wasn't installed right or something, but I didn't tear into it right then. A couple days later I drove it to work and was surprised that, when the engine heated up, the sound of the exhaust leak went away.

Still, when I first start it up, it sounds like there is a leak right up near the engine, until it warms up, then it's just the ruble of the header. I never smell exhaust while it's warming up, it just sounds like it's leaking. Any ideas what is going on? It runs great, smooth, doesn't rev up more than normal, it's just loud until it warms up.

This is only the second vehicle I've ever had that had a header (headers,) and the first was way too loud to hear any exhaust leaks anyway (and I could look down through my floor boards and see the coffee can that was squashed onto the broken section of pipe under my feet while I was driving it. Ahh, the joys of a bondo-mobile, way back in high school... Flame orange 74 nova with street slicks on the back, black fur interior and a 7 inch snorkel hood scoop on it. Looked AWESOME from a distance...) Anyway, any ideas of why it sounds like this? Is it something I will need to look into and fix, or is it normal?
You sure you're not just hearing louder engine/fan noise in general? The fan sounds like a small hurricane and the engine idles a bit higher than normal when it's warming up, they are pretty loud during warm up in my experience. I'm wondering if that's what you're hearing or do you feel like you're actually hearing leaky exhaust noise? I can't think of why you'd hear extra exhaust leak noise during warmup but it go away when warmed up.
 
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kjmagsig

kjmagsig

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Sep 14, 2021
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23
Location
Wisconsin
You sure you're not just hearing louder engine/fan noise in general? The fan sounds like a small hurricane and the engine idles a bit higher than normal when it's warming up, they are pretty loud during warm up in my experience. I'm wondering if that's what you're hearing or do you feel like you're actually hearing leaky exhaust noise? I can't think of why you'd hear extra exhaust leak noise during warmup but it go away when warmed up.
I'm pretty sure it's not the fan and it's not the engine revving. It sounds like an exhaust leak, but no exhaust smell. It's a weird one for sure.
 
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kjmagsig

kjmagsig

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Sep 14, 2021
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Wisconsin
Definitely sounds odd. Maybe you can video it and see if anyone hears anything?
That is a good idea. If I have time tomorrow afternoon, I'll make some recordings, before and after it stops. I was totally shocked when I discovered it had a practically new header on it. Looking at the body you would think this thing was never taken care of, but whoever had it last took real good care of the mechanics of it. Now I get to work on the body, and I know just enough about that to be dangerous. ;-)
 
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ytradio

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Aug 24, 2021
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49
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WV
An exhaust leak on a cold engine is pretty common. I personally would start by re torquing the header bolts, sounds like they were not re tightened or as we would say in heavy industry “hot bolted”. If you could re tighten while the engine is still hot all the better. Another good place to look is the header to exhaust pipe connection. This may be easier to hot bolt. Header flanges are usually thinner and harder to get a good seal than the beefier cast iron manifolds.
 

Gilaguy23

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Apr 12, 2021
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Q town New Mexico
My 91 does or did the same thing until I fixed the very front and missing rear manifold bolt. Cold running it sounded pretty bad but once warmed up and things expanded it was 99% normal sounding. It would be in your best interest to correct the leak though as in time it will worsen.
 
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kjmagsig

kjmagsig

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Sep 14, 2021
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Location
Wisconsin
Thanks for the advice. It's nice to know I'm not the only one to have seen this. I'll try re-tightening the bolts when the engine is hot. Does anyone know what they should be torqued to? Or should they just be tightened till they are tight?
 

Gilaguy23

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Apr 12, 2021
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I didnt torque mine,just did a by the seat of the pants torque being the gasket should be replaced eventually anyhow. Recon Im lucky its still not leaking. I will suggest checking all the exhaust brackets and hangers to make sure they are 100% effective. I fabbed a bracket off my bell housing to pipe to keep it from moving around in the rough stuff. I was working on a friends 91 and see my 91 should have a T case hanger and a dual rubber isolator type hanger behind the muff too. No wonder why my old exhaust self destructed. :cautious:
 

T-Rex Jeepster

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Middle Tennessee
When I bought mine....The exhaust manifold was completely broken through into three pieces. I had the 2.5 in it at the time and had no problem finding a replacement header for it.