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Topic Boards => Chevy - GMC Chassis => Topic started by: JonnyG on October 01, 2021, 03:49 PM

Title: Finding/Fixing Exhaust leaks
Post by: JonnyG on October 01, 2021, 03:49 PM
Where should I start looking for exhaust leaks and should I attempt to fix any myself? It sounds louder towards the engine and I can smell exhaust fumes from there

I’ve read that donut deals go often but anything that close to the exhaust manifolds will likely be seized right on won’t it? Should I just take this to a muffler shop?
Title: Re: Finding/Fixing Exhaust leaks
Post by: Eyez Open on October 01, 2021, 04:55 PM
The job is simple in itself, now if the manifold bolts are frozen it get pretty hairy. A acetylene touch would be needed and a knowledge of heating up the bolts..

Probably a shop would be in order. I'd call around and ask shops how they feel about such a job. Many have no clue in doing such a job.

Below is a video of the process, and that is easiest ive ever seen it done. Generally the bolts need to be heated to a cheery red and a lot of finess to get them moving. Brute force will just snap them off.
Title: Re: Finding/Fixing Exhaust leaks
Post by: cadillac_al on October 01, 2021, 07:58 PM
Mine just developed an exhaust tick.  I plan to lay under it when it is stone cold and have my assistant start it and I will feel for the exhaust leak.  I'm pretty sure it is a donut gasket.  It isn't too hard to change if the original brass nuts are still on it.  Those often get changed out to cheap steel nuts and get rusted and frozen on.  If the manifold happened to be leaking then it would be a tougher job to get the manifold off due to the tight clearance everywhere.  Here's to hopping it's only a donut gasket for both of us.
Title: Re: Finding/Fixing Exhaust leaks
Post by: TerryH on October 01, 2021, 11:57 PM
Old school way:
You said you have an assistant. Start it up, have he/she go to your tailpipe, rag in hand.
You position yourself under the tailpipe expecting to move continually forward. Upon your direction he plugs the tailpipe with his rag covered hand for 2-3 seconds. Continue moving forward, telling him when to plug it.  If the leak is downstream from the doughnut you will hear and see it. If between the doughnut and the head you have an exhaust manifold/head problem.
Title: Re: Finding/Fixing Exhaust leaks
Post by: JonnyG on October 02, 2021, 12:51 AM
That is sound advice, i will try that tomorrow. I had a closer look today and it looked like the nuts do not look brass. these nuts also dont seem to be sitting flush to the flange so maybe it was a poor installation? do those studs snap easy? they actually dont look very old or corroded and the donut looks shiney, i have a feeling they were replaced incorrectly. i read somewhere else that the crushed steel ones are preferred?
Title: Re: Finding/Fixing Exhaust leaks
Post by: eXodus on October 06, 2021, 04:26 AM
Those Ceramic donuts are fine when you got a newish exhaust system, but are rather difficult to seal when it's start getting old and deformed.
The Metal Crush Donuts are newer technology and more forgiving to this kind of imperfections.

When your studs/nuts are not straight in in that could be an install error.  Look downstream to see if your exhaust hangers are all there and not too bad stretched.

Yeah those studs might brake of when you apply too much force. Had it happen once. 
While the torch method works - I like to soak the nuts and bolts with penetrating oil for a day or two before I tackle them.

So spray them down - come back the next day - spray them again, come back the next day - spray them again - get my tools and start working.
Most of the time it works and I don't have to fight to much.
Title: Re: Finding/Fixing Exhaust leaks
Post by: JonnyG on October 07, 2021, 11:23 AM
I will try and source the crushed metal donuts, so far no luck finding them locally. might have to go online, im guessing they are aftermarket?

Any preference to penetrating oil? I take it that WD40 doesnt cut it?

Ive got a helper today to plug the exhaust for a few seconds to help locate the leaks, sure hope its not something else...

The exhaust all seems fine other some "handy" work just off the cat, someone tried stealing it and was scared off before they could complete the job. Previous owner did tell me about this and said they had the cut welded back up. Its pretty poor quality but seems to have fixed the leak. I have half a mind to just cut the cat out and put a test pipe in, would be quite simple though it seems as some of the folks around here frown upon that. There seems to be no flow restriction that I can tell so i think its still functional as far as i can tell. Anyone ever run dual exhaust out the driver side behind the front wheel? that sure would eliminate a lot of exhaust pipe.

I think I can hear leak and it sounds likes its under the doghouse, sure gets annoying in the highway. The wife and I end up nearly yelling at each other, surely this isnt normal?
Title: Re: Finding/Fixing Exhaust leaks
Post by: eXodus on October 07, 2021, 04:48 PM
WD-40 is better then nothing, but like PB blaster is a better one.

That welded exhaust could be culprit. Might not be straight.

I never had issues with cats. So I leave them alone.
Title: Re: Finding/Fixing Exhaust leaks
Post by: udidwht on May 01, 2022, 09:36 PM
Get your hands on a can of Kroil penetrating oil. Best stuff ever.

And when you button everything back up use a lot of copper seize.
Title: Re: Finding/Fixing Exhaust leaks
Post by: JonnyG on May 12, 2022, 08:06 AM
Does anyone have a part number/brand for the newer metal crush doughnuts? Was hoping to source them before taking them to a local shop that will actually accept a class A, its been harder than I thought it would be. The closest dealer doesn't seem to be very helpful and the shop im taking it to likely wont be giving me any choice.
Title: Re: Finding/Fixing Exhaust leaks
Post by: udidwht on May 13, 2022, 01:33 AM

Looked myself awhile back and could find no source for them.
Title: Re: Finding/Fixing Exhaust leaks
Post by: JonnyG on August 03, 2022, 11:29 PM
So I finally got around to getting my exhaust doughnuts dealt with. Found a shop that would do them, what a mess. It seems nobody likes to work on motor homes around here, they fixed them for a reasonable amount but then give me a quote for $1800 to have a single manifold changed out because its leaking? Seemed a bit steep to me so i will do some more shopping around i guess, i bet its just the gasket but they wouldnt give me further details. It drives considerably quieter without that exhaust leak now, i can actually hear my wife or listen to the radio on the highway. With the mileage that low and only ever driven during the summer i would guess manifold bolts wouldn't be too bad to take off, would they? Are 454's bad for warping manifolds or could it just be an age thing and need the gaskets replaced?
Title: Re: Finding/Fixing Exhaust leaks
Post by: Oz on August 04, 2022, 09:08 AM
Congrats on finally getting the donuts done. As for the bolts, the only way to know is by trying.
Title: Re: Finding/Fixing Exhaust leaks
Post by: Eyez Open on August 04, 2022, 11:48 AM
Chasing down old exhaust leaks is quite simple. One person plugs the exhaust pipe while another is under the rig listening...the pressure builds high enough hearing aids are not needed. 454 engines cook exhaust manifolds, I would start at the engine, and work towards the rear.

Now if your exhaust manifolds are leaking,salvaging them is highly doubtful. I've always used a scorched earth approach, heat the studs up to a cherry red with a high heat torch..acetellyn...shock the bolt with a quick burst from a water hose and then begin to break the bolts loose. I've always rocked them...loosen till you hear a pop, then righten then...back and fourth until they finally loosen. Never power them off,more than probably you will snap the head off right at the neck. One can also use a large hammer and beat the manifolds, that too will shock the rust..but RV s generally do not have the room.
Sound brutal ? It war take no prisoner's. Personally I detest exhaust work, a tourch and a air chisel are the essential weapons of war. Lift the RV take off the wheels,dismount the heat shields. The only finesse here is heating the exhaust bolts and breaking them loose. Heat the bolts quickly and beak them loose slowy.

The above is merely a opinion..did I say I detest exhaust systems..I've never seen one I've liked.
Title: Re: Finding/Fixing Exhaust leaks
Post by: JonnyG on August 05, 2022, 12:19 AM
Thanks for the replies. I took it to a shop because I too detest exhaust work especially close to the engine. An old friend of mine who was a mechanic for a couple years "claims" that spraying all those bolts down with liquid wrench for a few days and then trying to break them free with an impact gently is the way to go and that a torch is the quickest way to burn your rig down. Just repeating what he told me, I feel like the problem is 90-95% fixed with the doughnut and that chasing the last little bit is going to cause a lot of pain. you can hear the put put put on the right side but its not horrible.

Im hoping that the manifold gasket is cooked and just needs to be replaced, 40K miles but its a 1994. I would expect warped manifolds on a much higher mileage engine but Im new to 454's and dont really know what to expect. Is this the time to rip off all the exhaust and do headers with a short exhaust out the sides and call it done?
Title: Re: Finding/Fixing Exhaust leaks
Post by: Mlw on August 05, 2022, 01:58 AM
People are intitled to their own opinion. There is some truth in what he is saying because you really do have to know what you are doing and take precautions.

Out of my own experience I can tell you that even soaking for a few days doesn't always help. then somebody hit it with a torch and it came off with ease right away. Just saying that sometimes extreme measures are necessary to get the job done, but always with the right precautions and mind.
Title: Re: Finding/Fixing Exhaust leaks
Post by: eXodus on August 06, 2022, 05:24 AM
I had cracked Manifolds at 180.000 miles.

Tiny little cracks which made that distinct put put sound.

On quality headers you are going to spend a few goods bucks. Don't buy cheap ones, the 454 is really a very hot engine in the RVs