Bad seal at Exhaust Manifold gasket

[skipfletcher]

After doing a head gasket replacement on my 2001 Pathfinder, I cannot get my exhaust manifold gaskets to seal properly, causing P0134 and p0154 oxygen sensor codes.

I have replaced the driver's side gasket FOUR times, and it sounds good at first, but after the engine warms up, I can hear a gas leak. I've used Fel-Pro perforated style gaskets as well as multi-layer aluminum gaskets.

This weekend I went as far as replacing the entire exhaust manifold on the driver's side, new gasket, bolts torqued to spec, and got the biggest leak yet. So after the engine was warm I re-torqued, which made an improvement but not a perfect seal. And in fact, I felt one of the bolts start to strip, probably from inside the cylinder head.

I'm running out of ideas. Is my last option to use bigger bolts and re-tap the holes? Is there any way to ensure a better seal with the gaskets?

[4xq]

Try dry-fitting the manifold on the head (no gasket). You should be able to verify it fits flush and flat - i.e. no wiggling, and you can tell it is up tightly against the head on both ends.

If it fits flush without a gasket, then I doubt you have had 4 bad gaskets. I would start thinking clogged CAT converter. Might make sense given it takes about 30 seconds for you to hear a leak which may be caused by back presuure.

Hope that helps!

[rgk]

It put a chill down my spine to feel your bolt strip.

Maybe try threading the bolts into the head without the manifold to see whether they go in easily, and check the condition of the bolts. If they can't fasten properly, then a leak is unsurprising.

[skipfletcher]

I think I need to resurface the cylinder head mating side. It's rough and I didn't consider that affecting things. I also will just go ahead and re-tap the bad bolt hole and maybe more of them, and replace the studs. I think I'll also try some permatex ultra copper
So:
- resurface mating surfaces
- check cylinder head surface for warpage
- re-tap and new studs
- Permatex Ultra copper

And If that doesn't work I'll look into clogged cats. But I haven't gotten any codes that correspond to catalytic converts, and I don't get bad stalling as described in those cases.

[rgk]

How did it get so rough? Scratches from removal?

[skipfletcher]

May or may not be some scratches from a frustrated home mechanic struggling to remove/re-install the manifold. If memory serves it did look rough, probably also from stuff off the old gasket. I've also never felt great about the studs on this, what with the newer stripped problem, and previously with one that was clearly not screwed all the way into the head.

I just ordered an infrared thermometer to verify that temp at the outlets of my catalytic converters is hotter than at the inlet.

[rgk]

Don't forget to remove all traces of old gasket material. You might have to soak it periodically with brake cleaner, engine degreaser, or heck maybe even oven cleaner. Then scrape it with a hard plastic scraper. A metal scraper might be necessary, but you'll obviously have to be careful.

[skipfletcher]

Will do.

I think I'll also throw some cat cleaner in the fuel tank just for s's and g's, as well as checking the inlet and outlet temps. It's not out of the realm of possibility that there is some clogging in the cats since this whole escapade started with a head gasket failure.