Leaking collector flange

I've been having exhaust flange leak issues so recently I got some pinched head nuts that should not vibrate loose for the exhaust collector flange connection. I installed them and experimented with two different gaskets, one is the standard asbestos type and the other was an aluminum gasket.

I then had a friend hook a smoke machine up to the tail pipe and both flanges were still leaking. The alum gasket leaks worse than the paper/asbestos one.

My LT fuel trims are out of whack (+15-20%) and the flanges are upstream of the first O2 sensors so I need to fix the leaks in case the air ingress at the flanges is messing with my O2 sensors and thereby messing with my fuel trims.

Anyone have any experience with sealants in addition to the gaskets?

Copper RTV does great things!

Thanks Erik, I just picked some up. The directions say not to torque the bolts down to tight as that'll squeeze all the rtv out. What do you do?

Also, on my car there's a vacuum line off the back of the manifold that when connected to the valve in the coolant lines closes the valve such that there is no heat available inside the car.

I just remembered that vac line on my drive home from work and closed it with a golf tee when I got home and my LT fuel trims came down from about 18% to about 10%. Doh!

I wonder how much more difference rtv'ing the exhaust flanges will make, tightening up the flange bolts dropped my LTFT's from about 22% to about 18%.

acorad wrote:The directions say not to torque the bolts down too tight as that'll squeeze all the rtv out. What do you do?

Let it set-up a bit (10 min's or so) then torque down.

Thanks LT1.

Well, the fiber gaskets blew out already, even with being coated with Copper RTV when assembled. I've ordered copper gaskets and will use the Copper RTV again.