I've got a major leak at the ring-type "donut" gasket where exhaust pipe meets exhaust manifold. It puffs like a dragon anytime the engine is on. I recently replaced the gasket while rebuilding my top end and it was an exact fit. In fact it's leaking so badly that it's fooling my downstream o2 sensor and I'm barely getting 20 mpg. Getting the engine rpms up higher makes the cab air quality unbearable, I have to drive with the windows down everywhere I go, and wear a thick jacket because it's freezing. I'm thinking since the vehicle sat for 11 months with the pipe detached, that the angle the pipe comes in at may have changed. It only leaks from the bottom side of the donut, and I just don't know what to do. I've tried over-tightening the spring flange bolts but to no avail. I'm about ready to just exhaust weld the whole thing over and chip it loose if I ever need to replace parts again, but that's just asking for trouble.

So is there something obvious I missed?

 

"puffs like a dragon"?
Do you mean smoke and all, or just a really bad leak?

I would take it back apart and make sure the surfaces all mate correctly. It sounds to me as though the donut isn't fit correctly.


Joe