I'm not sure if its actually a leak but after I installed my Megan Downpipe last weekend I've been hearing a hissing sound towards the front of the car. I would like to know what is the best way to check for a leak at the downpipe and stock O2 housing. The way I installed it was just using the stock doughnut gasket on the O2 housing. I'm not sure if I damaged it while insalling the new one. Is it better to use the doughnut gasket itself, take off the doughnut and use the provided exhaust gasket, or use both to hold the best seal? Thanks-Eryk

 

You´ll have to verify that the stock donut is in good condition otherwise purchase a new one from the dealership. Loosen the DP/cat(or test pipe) bolts first. Then tighten the O2 housing to DP bolts. Lastly, retighten the DP/cat bolts.

You have to tighten the O2 hsg/DP bolts first while the DP/cat bolts are loose. This assures a tight flat parallel seal between the O2 housing flange and the DP flange faces.

 

is it a bad idea to use both gaskets? I heard if two are used then one usually fails

 

So i still don't know what to do. Should i get a new donut gasket? Should I take off the donut gasket and replace it with a regular exhaust gasket? What are you guys doing to keep the seal?

 

Get a new donut gasket. It should solve your problem.