I bought a new MAC Y-Pipe and it fit right up and tightened down but there is still a good leak between it's flange on the passenger side and the manifold. It the kind that "flutters" or "chuffs" a bit when the engine is cold and then closes up when it warms up. I can see black exhaust marks above the flange on the manifold. The shop advised I disassemble and reassemble with Permatex Ultra Copper and let it sit overnight. Any other recommendations?

 

Are you using the cast iron spacer or a donut?

 

Yes, it's in there.

 

What's leaking... the joint between the spacer and the Y-pipe, or the one between the manifold and the spacer?

 

The spacer and the Y-Pipe. It feels firm when wiggled and I've tried to reseat it once with no improvement. Bolts are snug and the flange retainer plate seems down all the way.

 

Drive it for awhile; take it back apart, there will be a telltale of black gunk where it leaks. See https://www.thirdgen.org/forums/exha...edlebrock.html for an example. (although, the leeeek in that photo was undetectable, I had no idea at the time that it was anything but perfect, but if yours is yuuuuujjjje enough to be audible, it will be OBVIOUS) Then you can figure out what you need to do. Might be you need to grind or wire-brush or otherwise treat the spacer; might be a defect with the Y-pipe; might just need a schmeeeeer of ultra RTV. Observe carefully and UNDERSTAND what's not sealing before randomly applying some "solution" that … isn't. Including just spoooojing it.

 

Did you use a gasket on the flat surface between the spacer and the manifold?

 

No. Is there supposed to be one? The surfaces looked machined

 

Which one? A donut, or the cast iron spacer? Not sure it matters, but might help to know.

No, no gaskets anywhere in a thirdgen exhaust. That also means everything needs to be clean, since any garbage getting in between the surfaces can create a gap.

Exhaust leaks are fun. Sometimes they'll carbon up and corrode, sealing small leaks. Other times the jet of hot gasses will erode the surfaces around the leak.

A high temp sealer might help make up for a minor mis-match of the Y-pipe and manifold flanges. Also make sure you're tightening the clamp bolts evenly. Get it cocked, or over-tighten one or the other bolt and you can misshape the flange or otherwise create a gap.

 

Yeah, that is what I thought, and as Drew stated there is not gasket there from the factory. The mechanic at the shop I took my car to made a gasket out of the high temp material similar to the manifold to head gasket. He said I needed one there. Well all I can say is mine does not leak on that side. It is to much coincidence that the pass side is fine and it has the ball type socket on the manifold itself and on the drivers side it is a flat surface seal? Seams prone to a leak if you ask me.

 

Yeah, I would think also but the exhaust marks are on the flange to the Y-Pipe. Regardless, I will follow Sofa's suggestion and remove it in a bit and check for marks.

 

Was there any rust or corrosion, dirt, etc on the spacer when you re-installed it? I blasted my spacer to bare metal and painted it with 1200 degree paint. I installed a gasket between the spacer and exhaust manifold (although I know you said yours is not leaking on that side)...

 

Steven; Be careful not to let anything fall into the pipes when your workin' on this ! I know full well that it can be a bitch to get that spacer into a good position when installing the Y-Pipe,... especially if the exhaust is connected to it. In short: Set the pass side first, then the drivers side.

Have a tube of high temp sealer ready as well as a wire brush and maybe some quality steel wool. Best bet is to disassemble the Y from the manifolds & just clean all surfaces as best you can. AT LEAST disconnect it enough to remove the spacer so it - and the flat mating surface - can be well cleaned. Use your finger to wipe sealer on both flat mating surfaces. Good idea to do the same for the ball/socket side to,... once there is a thin coat on the ball socket side apply just a little bit more sealer to 1 surface, then put the spacer on the top of the Y-Pipe and move on. ( NOT a lot of sealer; you want to see how the ball/socket is fit together. ) Spread a little bit more sealer on the thin coat to the manifold flat and then fair amount on the flat surface of the spacer. Keep heaviest application of sealer to the middle/outside of the spacer rather than close to the hole, don't wan't excess to fall in the exhaust once tight. This is where most leaks are found & you don't need to see this area as clearly so a bit more sealer is OK. ( The position of the spacer here is important; Kinda' tough to keep everything in place and make adjustments with only 2 hands ! )

Once your ready to install the Y pipe, get the drivers side lifted into position and leave all the nuts loose on the studs, let it hang. Then go tho the pass side and start the real work. Get the pass side lined-up and mounted as evenly as humanly possible. Snug the nuts little by little making sure that the spacer is aligned as well as it can possibly be. ( might need to raise/lower the drivers side as your doing the pass side for the pass side to fit as well as possible; a helper here is GREAT ! ) Once you feel it's as good as it gets----> tighten all the nuts firmly/completely on the pass side.

This will install the pass side in the best possible place to avoid leaks. It will ( almost certainly ) make the drivers side fit like crap. You want to finish the job before the sealer "sets-up" so have a couple crow-bars, pipes, long screwdrivers, jacks, and wood blocks at the ready for the driver side work. Use what-ever method required ( jacking, blocking, leverage, etc.... ) to properly position the drivers side manifold/Y and tighten up that side completely.

Don't start the car for at least a day; On day 2 start and check for leaks.

Good Luck !!

 

Speaking of dropping things in pipes... I parted an 86 Firebird with an LG4 long about 15 years ago. When I pulled the Y-pipe I could hear something rattling. I shook it and banged it on the ground and an offset combination wrench fell out of the exhaust. Bet that drove the crackhead that owned the car crazy. Maybe that's why he drove it into a parked tree?