Exhaust Flange Leak
I recently replaced the exhaust on my 360 with a used F430 exhaust system. I have noticed that at start-up when cold, as the water condensation begins to form, that water is pooling up on the top surface of the exhaust flange (where the muffler mates to the exhaust tips) and also a small leak of condensate from between the the flanges indicating a bad seal / gasket. I removed the muffler and examined the mating surfaces to discover that the bottom flange plate (on the exhaust tips) is not perfectly flat. There is small gap between the mating surfaces that is measurable when mating the muffler flange ... maybe 0.020" when measured with no gasket in place. It appears that using a new gasket is not going to fix this problem as the gasket material is fairly thin and in order to seal properly, the two flange surfaces need to be more flat than is the case. In addition, I suspect that the weld around one of the exhaust pipes at the joint to the flange may need repair.
I am going to try to use a flat file and some elbow grease to see if I can get the bottom flange a bit more flat. Also, see about getting the pipe / flange weld renewed.
Next question ... has anyone used Permetex Ultra Copper RTV Silicone? It is rated to 700 deg F. I have seen several reference in other forums (Corvette and others) where this product has been used successfully, especially in cases where flanges may not be perfect. I am thinking of applying a coat of that compound to both sides of the exhaust gasket, hopefully, to fill any minor voids.
Last question ... has anyone substituted the single dual-hole gasket and used two donut exhaust gaskets that one can acquire at NAPA, etc.
I am attaching a pic of the water condensate collecting on the top left side flange. Appreciate any comments.