Saab: 1993 900s maybe exhaust smell in car?, exhaust pipes, oxygen sensor

Question
QUESTION: Jerry, I recently had my right inner driver replaced on my 900. To do this the saab mechanic had to drop the exhaust on the passenger side to do the fix.  When he reattached the exhaust he put the new gaskets in(2),used gasket sealant, however, one of the old rusty studs broke on one of the exhaust pipes, so he drilled in a new bolt. Am I thinking that exhaust is leaking from one of those gaskets and coming into the car through the vents or is this something that I am congering up in my head? When the heat is coming through the vents in the cabin, where is that air coming from? There was no smell before this repair, so maybe I am just imagining this.  Thanks, Mike



ANSWER: Mike:
 You haven't stated that you are actually 'smelling' or otherwise detecting any fumes. Of course, you should be wary of any leaks, and an easy way to check is as follows; With the engine running at idle, ask someone to temporarily 'block' the exhaust with a large rag, etc. so as to build up internal pressure in the exhaust system. Then, place your hand  near the area of the joint that you suspect is where a leak might be...try to feel for puffs of air and/or listen for any evidence of a leak.
  From your description, however,I doubt that the stud replacement would affect the joint integrity, especially since the mechanic replaced the gaskets and used gasket cement.
 And by the way, the air from the heater ducts originates outside, through the vents just  below where the windshield meets the hood area.
  But, if there is the slightest chance of there being a leak, make absolutely sure that there are in fact, NO LEAKS!

   Hope this helps.

---------- FOLLOW-UP ----------

QUESTION: Thanks Jerry, We found that there was a small hole in the front pipe where it attaches to the cat.  I replaced the front pipe and had to use a new oxygen sensor because it was rusted so bad that it stripped when we tried to remove it.  Anyway, my question is when he attached the front pipe to the manifold he used two new gaskets but did not use gasket sealant.  He said that the new gaskets without the sealant would seal it just fine.  Is that right?  Thanks, Mike

Answer
Mike:
 Gasket sealer is generally NOT necessary as long as the mating surfaces are reasonably flat which they almost always are. Because of the hi temperatures involved, most gasket sealers are ineffective anyway. Your mechanic is right.
         Jerry