OK, so I've had exhaust leaks ever since I put the downpipe on the car. I'm really f**king tired of it, so during my tranny rebuild I had all exhaust flanges reground by a shop using their big belt sander.

Today I go to bolt it up, and tighten the crap out of it. I'm using a double-layer of Mr. Gasket gasketing, with a bead of silicone RTV between the gasket layers. I bolt it up really well and still there is easy a .005" gap in the middle of the flange.

I need some help. See pic.

Dave

 

Well, figures. As soon as I walk away from posting this, I come up with an answer:

when I peeled apart the two layers of the flange, it's really easy to see which part of the RTV wasn't squished tight. So I take some more Mr Gasket, use a razor to shave it so it tapers to thin at the ends, and size it to cover the area that isn't compressing. So the final gasket is thicker in that area. Another bead of RTV to put it back together (I'm going to use a heat gun to try and cure it quick), and it looks like it should fit like a glove. The trick is the RTV between the gasket layers - it told me where to thicken the gasket.

 

The RTV will hold up to that kind of heat?

 

It's the copper silicone high temp rtv. I figure it should hold, but the mr. gasket material is pressed so tight I don't think the rtv is doing much sealing.

Warped flanges suck. I think I've spent 40 hours over the last year screwing with this friggin leak.

Dave

 

I have had an exhaust leak since installing my down pipe as well and have not been able to determine the source. This last weekend I installed the efini ypipe and thought that with all those components removed I would be able to find the source of the leak. What I did find was a sooty deposit on the old y pipe engine side next to the turbo actuator assm. But I still could not see where the leak originated. I had a suspicion that it was the downpipe but that was not the case. Any feedback you may have for me would be great. At this point Im thinking its probably the exhaust manifold. Without pulling the turbos I probably wont be able to resolve this. My car only had about 20,000 miles on it when i put the down pipe on last year, so I would be surprised that it could be the manifold. But who knows?
Was there a sooty deposit on you components from your leak?
chuck

 

Yes, there were soot traces.

That sounds for sure like a downpipe exhaust leak - so I suggest checking the following:
- using mazda hardware for the bolt/nuts
- lightly sanding the metal gasket and mating faces
- flatness of the flange(s)

So when you pull the downpipe, the colors on the gasket should tell the story if it leaked or not. If there are no leaks, I suggest removing the 4 bolts that hold the cover to the precontrol door - if the leak is there you can save pulling the turbos.

Dave

 

I am almost positive that the downpipe was not the source of the leak. When I installed the downpipe, I cleaned the joining surfaces, cleaned the metal gasket, and checked the downpipe mating surface for flatness. I used stainless socket head bolts which i torqued and retorqued after running the car. When I pulled the oem ypipe I checked the downpipe bolts and they were still tight after almost a year..
As far as the cover for the precontrol door, I am going to have to get into my shop manual and parts breakdown to find out what that looks like and the location. Besides the downpipe and efini ypipe, this area is unexplored territory for me.
I remember seeing a post that talked about a bolt somewhere in the turbo area that can come out or loosen up which will sound like an exhaust leak or was an actual exhaust leak.
There is a strong exhaust smell and the sound is kind of a sputtering.
The sound might even diminish slightly as it warms up, but not a lot.
chuck

ps thanks for your input

 

First off, you should NEVER use RTV on exhaust gaskets. All that does is create a failure point - the RTV blows out LONG before the gasket will.

That said, in the first pic it looks like you have an alignment problem. What exhaust components do you have on the car? What brand downpipe?

I had a buddy of mine with a busted passenger side motor mount - the downpipe would hit the frame of the car due to the engine sagging. All the flanges should line right up - if they're off by quite a bit, something is wrong somewhere in the system.

Cheapie parts store gaskets don't cut it either - you need quality, heavy duty gaskets. The stock Mazda gaskets are of good quality, as are the gaskets that come with most downpipes and the like. I installed an HKS downpipe for a friend, and the crappy parts store gasket we used leaked instantly.

Make sure when you install the exhaust, you go from front to back, and keep all the fasteners (save the downpipe-turbo) loose until all components are lined up and in place. If you tighten one flange, you can "torque" the exhaust in the hangers and cause it not to line up with another flange.

Dale

 

Ok, well I got the car started up tonight, it seems the leak is gone, based on the sound.

I have a Pettit downpipe, stock cat, and RB dual cat-back. In this case, I fastened to cat-back parts first, then to the stock cat, then the downpipe to the manifold, and finally the downpipe to cat. They did not align naturally, I had to push the exhaust back in the rubber hangers quite a bit. The mounts are good, the pipes are generally in the right place, except that it seems the overall exhaust is a little too long. The 2-layer gaskets I made probably don't add more than .25" over what was there before. I'm guessing 1" shorter overall would be about right.

It turned out the warping is not in the plane shown by the picture - actually the bottom side of the cat flange (away from teh bolts) wasn't putting pressure on the gasket. I used a .0015 feeler gauge to probe the flanges for tightness. Once I figured where it wasn't tight, I loosened the flange and inserted a sliver of gasket material and retightened. It took a few tries to get the gasket sliver shaved right to get an even seal all across the bottom.

The RTV was used to keep the two layers of gasket together, and based on what I saw the first time I disassembled, was squeezed out so much it was not performing any sealing duties. I might leave it out next time, but for now I'm not concerned.

Dale, thanks for the tips - next time I'll put it together in the order you described. I've spent a fair amount of time researching this subject (pesky leak) and found very little info of substance until now. How do Mr. Gasket and Fel-Pro gaskets compare to the stock precut gaskets?

 

I have used only red/orange RTV sealant for my exhaust gaskets. No additional gaskets or anything and I haven't had any problems with leaks. Maybe I'm lucky.

 

I use (don't laugh--it works) GE Silicoln II door & window sealant (clear). Yea, the stuff you buy a Home Depot in the big tubes for $4. I've used this for the last 25 years and it's better than anything else I've tried, including the RTV Red, which it replaced.

I've used it to attach headers, and exhaust manifolds without gaskets as well as exhaust flanges (w/gaskets)--including the very one at the subject of this thread. It also works for many other sealant applications as well.

The key is to apply it and then allow it to setup overnight before you fire the engine. Also be sure you're using fresh product. This is the only sealant that I've used on exhaust systems that has never leaked, even with poor fit up. In fact, the only problem I have had is getting the manifolds and headers off. I could actually stand on the headers and not break 'em loose without additional persuasion.

My approach may seem unorthodox (to some, at least) because the product is not labeled or endorsed for automotive use, or does not say RACING, but it does work and work really well.

 

I just look at the way all automotive manufacturers do it - flat flanges with a quality gasket. A good gasket will hold up for a long time, doesn't need to cure, and can typically be reused MANY times.

I know there are good aftermarket ones, but there are also crappy aftermarket ones. I just know what the good ones look like .

Check out the pic of the gasket Racing Beat sells -

http://www.racingbeat.com/resultset....rtNumber=16340

That's a quality gasket. Metal ring in the center and a quality material for the gasket surface. The ones that look like dark grey paper don't cut the mustard, or ones without the metal ring.

Dale

 

I have one of those RB gaskets (3"), and a few of the OEM (2.5") ones of that design. I agree, they're probably the best and they can certainly take the heat.

But to how narrow the flange is, and that the stock cat has different pipe ID than the muffler and downpipe, I was concerned about it not sealing well. Plus, that's the kind of gasket that was leaking to begin with. I'll report back on whether the Mr. Gasket stuff takes the heat.

If I had a high flow cat with 3" pipe those gaskets would probably fit perfectly since all the pipes would be 3" and the metal ring would make a tight seal.

Dave

 

Use some muffler weld paste.

:-) neil

 

Good luck on the trial Dave. I bought a RB gasket also and used it for my DP. So far no leaks (crosses fingers).

Jeremy