Repairing Exhaust Leak on my 300zx

As I talked about earlier, I replaced the catalytic converter. What I had hoped would be an easy install turned out to be a royal pain. I went with a OEM style 300zx catalytic converter which should have been a bolt on job. But since the bolts connecting the cats to the exhaust manifold were so rusty, I ended up having to break the nuts and drill out the manifold.

I put the Wasp back together, and was happy to go on my way. But the exhuast didn’t sound right, and I still had a strong exhaust smell. This smell was different than before (pure exhaust, not rich). Checking under the car I can feel exhaust gas coming out where the cat-back exhaust connects to the catalytic converters.

I tried tightening, re-doing, doubling the gaskets… but still the 300zx exhaust leaked badly.

After multiple failures, I decided the problem was that the cat-back exhaust had a slight bit of pipe extending past the flange. It certainly seemed to be causing difficulties mating up the flanges. So I took the exhaust apart again, ground the cat-back lip off, and re-connected the exhaust. Leaked like a mother!!!

At this point I was ready to fling wrenches, but I decided to try one more thing. I had already purchased some high-temp gasket maker. I had hoped I could avoid using it because I’m worried the temperature will be to high at the flange since it will be following the catalyst. But I decided it was worth a try.

I took two exhaust gaskets, and laid a 1/4 inch bead of gasket maker on each side. One advantage of the gasket maker was apparent immediately – I could just press the gasket to the flange in the right spot and it would stay on while I got the exhaust bolts on.

I tightened the exhaust bolts until I could see the RTV gasket maker starting to squish out of the the sides of the flange. I left it like this for one hour, and then came back and tightened the bolts down firmly.

I let the car sit overnight (having finished at noon) to let the gasket maker cure completely.

Started her up this morning, and FINALLY the 300zx isn’t leaking exhaust

1 Comment

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  By Kevin, May 23, 2014 @ 11:34 am

  Update: The high temperature gasket maker has held up just fine. No more leaks!!!

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