After replacing the entire exhaust system (and head gaskets and other gaskets) on my front-wheel-drive 1990 Olds98, I eventually found that aftermarket manifold pipe (aka "down-pipe from manifold to cat converter) has a slightly different flange shape that leads to sneaky exhaust leak. My car had a rigid (not flexible) manifold pipe. I used paint brush to apply thick soapy water around flange donut area with engine cold. Then started car and revved throttle.... It would leak visibly (big bubbles) only when throttled. Without a soapy water test, you could not hear the leak for sure even if you listened using a hose or stethoscope. I recall that the flange on the orig (OE) manifold pipe was somewhat globular shaped inside whereas the aftermarket one is more of a funnel shape. I also was informed that this joint or union (for lack of an official term) is designed to flex like an elbow when the sideways mounted engine banks rearward a tiny bit during throttle. You can actually see the joint flex like an elbow, but only an almost imperceptible 1/16th of an inch. If the aftermarket flange is not perfectly shaped true to the OE flange, it will deform the new donut gasket ever so slightly and cause leaking exhaust. Also, the aftermarket flange might cover less of the donut. And most importantly, this is piss poor engineering from the GM gitgo. Some FWD GM exhaust manifold pipes are flexible and may thus avoid bending the joint and leaking at the donut. Mine had a rigid pipe (at least since I inherited this old Olds from my late father) and it did not appear to be post-factory. Unfortunately, I threw out my old manifold pipe and now must track down a GM OE salvage replacement to replace the new pipe that I should have never installed. I also plan to install a performance flex coupling from Summit Racing on the manifold pipe in hopes of eliminating stress on the flange joint. I wonder if people have actually wrecked and died from carbon monoxide poisoning because FWD drive cars have poor flange joint designs. These things are unsafe at any speed. That's my opinion. Don't sue me.

Welcome to TOC-



Probably not many, if any at all, but I am assuming you are making some sort of joke about the problems with your leaky exhaust.



Any car is only as safe as it's operator.

Welcome aboard- Hope you find things here to be a better design...

Andrew

No, I was surely not joking. This exhaust leak has been gassing me for a whole year and persisted after rebuilding entire exhaust system, having it welded, replacing head gasket, exhaust header gaskets, crossover gasket and flange gasket and replacing some gaskets multiple times and testing everything for hairline cracks or warpage (none found). I also replaced the two flange springs and studs with exact identical ones. And I temporarily closed off the EGR copper pipe and EGR valve for a week as a test during driving (no leaks there). all vac lines were in perfect order and intake and throttle were likewise reassembled with new gaskets everywhere. Professional muffler shops I consulted did not offer any specific method for locating the leak other than listening and feeling. You cannot blame the safety issue on the operator of a vehicle who practices every due diligence to repair something. I was unable to find this answer after consulting Mitchel Online, my Haynes manual, a million websites, countless mechanics and seasoned mechanic friends until one mechanic suggested the soapy water test. It was only recently that I observed the flange union flexing like an elbow ever so slightly when engine is throttled. Most mechanics are probably not aware that this flexing even occurs since it is so hard to see. Flexible pipe segments are sold by performance shops specifically to isolate engine vibration and torquing from exhaust systems. And given that front wheel drive cars have sideways mounted engines, it would seem the engineers at GM were obviously aware that the tilting/torquing of a sideways engine during throttling WILL in fact stress the flange union. Now if in fact my old Olds came with the rigid downpipe (manifold pipe from manifold to cat converter) then that is a design decision that is subject to legitimate safety concerns. One can hypothesize that the engineers calculated specific levels of stressing and torquing and found them to be fine. And in fact, I do NOT recall any exhaust leaks until I replaced the downpipe with an aftermarket one which came as a unit with cat converter when I had to replace the cat (the incident that started the whole process). My big mistake was noticing that the new downpipe had a slightly different flange internal curvature (conical instead of spherical) and then trusting it. I am fully convinced that the aftermarket downpipe is improperly designed and cannot flex like an elbow at the flange union without distorting every new donut I install. Apparently, from what I've been told and from observation, the OE downpipe from GM had that spherical internal shape inside the flange specifically so the flange joint could flex properly without distortion. Thus, it took me forever before I was able to determine that the new downpipe flange was the culprit. And so I posted my post as a caveat for others who may encounter the same problem. The GM orig downpipe flange was not at fault. Nonetheless, if this Olds was manufactured with a rigid downpipe, it's my strong opinion that this is an unsafe manufacturing practice for most FWD cars unless there is a better way to isolate the engine torquing from affecting the flange union at the donut. The elbow motion would appear sufficient to distort the gasket improperly over time, even with the higher quality original flange and downpipe. The important point here is that I hope readers of this forum will take notice and give critical decision to the fact that aftermarket flanges may NOT safely meet OE specs and in my case they did not. Perhaps the aftermarket mfr was unaware how critical the internal shape of the flange might be to forming a proper seal under conditions of elbow-like flexing of the flange union as intended by manufactures of this kind of car. There is no way that this car is unsafe because of its operator. I work hard to investigate the best fix for everything and then do it. Likewise, there's no joking about carbon monoxide. From what I've come across, there are some statistics saying that a huge percentage of automobile collisions are caused by exhaust leaks. I realize that many of these are because operators do not take care of their exhaust systems. But to the contrary, if you understand some very basic principles about stress and design, you might begin to accept the proposition that Ralph Nader was right when he wrote the book titled "Unsafe at Any Speed" decades ago. The effect of carbon monoxide can be deadly if you are not extremely careful to minimize driving. It's very easy to black out on the road. And rolling down the windows can sometimes make it a lot worse. Incidentally, my original downpipe is regretfully gone forever and GM dealers no longer stock them. Time to search the salvage yards. I do not need any help from anyone here on this issue unless you have had the same specific problem and care to expand on what I've said. My message is merely intended to share my experience and wisdom with others. And yes, despite the fact that cars are "engineered" there are countless unsafe aspects designed into cars. I'm 57 and have owned three GM vehicles so far. I am preserving the Olds 98 mainly because it's sentimental and I got it from my dad when he died. I've found countless shortcomings in the quality of GM and many other cars in the way they are built. Nonetheless, this 1990 Olds 98 has under 55,000 miles. The engine condition is excellent with lots of spunk and the body is coming around.

Hi oldolds,

Welcome to TOC.

I see by your profile, you are 101 yrs old and have a 38 liter (about 2,300 cubic inches?) engine in your 98.

I am impressed.


This tells me, it is not much of a leak.


You have an aftermarket head pipe that does not fit properly.


Because you have an aftermarket head pipe that does not fit properly?


I would be interested in knowing how much it will leak.


Your assumption is that the design is actually flawed, not a quality control or production issue. It also assumes that it was ongoing throughout all the production runs.

You also assume that enough CO could get past the airflow in the engine compartment, migrate into the cabin, then through the airflow from the ventilation system, to even be measurable.

More than the normal amount of CO, from traffic, that enters the ventilation system?


In that case, they should have never been allowed on the streets/highways.

Norm

Dear 88 Coupe, Your post is beyond the boundaries of civility. I think it is both incorrect and inappropriate for you to come onto this forum and summarize that I am a "BS artist." THAT IS PURELY ABUSE OF ANY FORUM. I am not here to harass anyone. Nor have I posted anything that is not truthful, accurate and sincere. I am here in this forum for the sole purpose of communicating with mature and fair-minded fellow mechanics with a level headed open minded attitude. I have come about my own results by meticulous and painstaking investigation as any mechanic does when he cares about the condition of his car. All of my work is photographically documented. You have piled on a large number of statements challenging my credibility. I will not go on the defensive by answering them all. The exhaust leak has been very real and has had nothing to do with cars in front of me when I'm driving as you further state. I'm not here to get into a contest with anyone to prove who can win an argument. I respect ALL users of this forum and I have NOT engaged in any BS or idiocy or posted any crap. You have every right to respectfully disagree with me. But you do not have any right to call me a BS artist or disrespect me in any other way. I realize that a majority of people might even question the credibility of my statements on the issue of the exhaust flange union. I am not new to controversy. I am not new to swimming upstream or going against the grain. If you were here I could demonstrate every detail of what I have stated. I respectfully disagree with your attitude.

Care to share the documentation? To be straight forward, either you are sitting on a gold mine of information, or you're blowing smoke. If you aren't making it up, I don't understand why you don't want to talk about it.



With all due respect, if you didn't want to discuss it, the question becomes, "Why did you post it?" If you'd rather not talk about it, say so, and it will go away. I don't think anybody here is looking for a fight, except maybe 91parkave...



So your claim is that you bought an aftermarket part that had the wrong type of flange, causing the exhaust to leak at the manifold, which in turn makes the design of the car unsafe at any speed? This is almost like reading those "9/11 Truth" websites- looking for the conspiracy where it just doesn't exist.

Sorry, I don't buy it yet. I'd like to discuss it though. I don't understand how the car design is a problem when there wasn't a problem before you replaced the catalytic converter.

I also don't understand how a small exhaust leak at the manifold is gassing you out of the passenger cabin. Do you have other leaks or holes in the firewall or something?

Somewhere in here is a logical explanation for why you are the first person I've ever seen making this claim about these cars. The answer to that question is also the solution to your problem.

If this were a common problem, or a serious problem, you would think that with 1 million + of these cars on the road, more than one person has put aftermarket exhaust on one of these cars- It just doesn't add up.

Regards,
Andrew

And your personal attack, is not?


I think it is both incorrect and inappropriate for you to read something into my post, that I did not write?

Since you brought up the subject: It is interesting to note that personal attacks are the first tool of choice, for BS artists, to avoid discussing their own statements.


Obviously, I'm not there. And from your aggressive posturing, I would not wish to be.


I have no doubt that you could do it in a scientific manner.

Since that is not possible, you might consider discussing it here.


Attitude? Not "politically correct" enough for you?

I don't claim to be 101 years old and have a 2300 cubic inch engine in my Oldsmobile.

Norm

I've read Nader's book more than once. What it dismisses is personal responsibility for one's actions. I can't agree with the school of thought that says because I neglected to either maintain or repair something, the machine that failed is at fault, and is unsafe. He has some good points that have led to developments in vehicle safety that we use today, but for the most part I don't agree.

The operator of a machine has the responsibility for maintaining control of that machine. Part of the risk of operating high-speed, heavy machinery is that if you don't pay attention to what you are doing, you can be seriously hurt or killed, or seriously hurt or kill others.

Saying we need safer cars, or that a car is unsafe is just giving permission for, or condoning people to be neglectful and irresponsible.

I do believe that safety features in cars are a good thing, as the neglect of others and ourselves can necessitate the need for them. It's just that these features don't really make the cars any safer. You can still go right out and plow into somebody.

Doing so, is the basis for our Tort (deep pockets) system.

I am reminded of the fatigued car owner/driver who fell asleep at the wheel, left the highway, overturned, and sustained spinal cord injuries. Paralyzed, he sued the vehicle manufacturer, for negligence, and received millions.

Nader's book was a big contributor to this kind of mentality.

Norm

When I replaced the exhaust system on my 1988 Delta 88 with the 3800 V6, I replaced everything from the exhaust manifold to the tail pipe.

My experience with the after market exhaust systems for these full sized cars based on my Delta was ok. I was told by two local parts stores that they only had part of the exhaust system in stock, sighting the original equipment being stainless steel, and often not replaced because the original parts would outlast the rest of the car (mine made it to 320,000 miles).

1) I had issues with the pipes/etc not being 100% perfect fit, but I got it together without too much issue. I did weld the pipes together like the original system.

2) Is the exhaust leak between the manifold and down pipe or between the down pipe and catalytic converter?

I don't see anyplace where Norm started out calling you names, seems like you may have read his signature as part of the post?

you know i just read this entire thread and damn for once i have to take 88coupes side, everything norm mentoined to you is on target you should take that advice instead of wasting more money.

91buickman "takes Norms side" against a BS artist.

How funny is that.

Norm

its your advice in this matter i saw as dead on, beyond that aspect your still the same BS master, but merry christmas and a happy new year

And yet another one went over 91buickmans head.

Norm