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Exhaust leak at header / downpipe seal - what can I do?

gone postal

NAXJA Forum User
I replaced my cracked manifold a few weeks ago b/c the XJ was getting terrible mileage (13.5mpg city and it's a stock vehicle). So, I installed an APN header and for the life of me, I can't get it to stop leaking at the crush pipe connection. The metal "seal" is in there and I can't tighten the bolts anymore if I wanted to. It leaks out of the sides - ie - the bolts are a top-and-bottom configuration, so the leaks shoot towards the oil pan and the frame. This basically puts me back where I started!!! Can you buy replacement seals at autozone? If so, what is it called? I took it all apart today and tried to get it to sit in perfectly straight, but that still didn't help. Is there any sort of "gasket maker" that can handle that type of heat?
 
Okay, thanks.

Now, seeing that this was a new gasket (came w/ the APN header), is there a trick to installing this so that it doesn't leak? It seems as if it's shrank / been crushed and turned brown, but didn't create an airtight seal. I alternated between tightening the bolts so that it wouldn't crush in an ununiform manner.
 
New "donuts" (that's what they're usually called. It's a quick check to see if your parts guy is on the ball...) typically seal well right out of the bag, as long as they're not damaged in transit. If you're paranoid, put a thin layer of RTV copper on the outside of it before you install, and you'll be fine (but I've never needed to. I know the copper will work tho - I use it on manifold gaskets all the time.)

Sounds like you're doing it right tho - tighten alternately and evenly, and try to not exceed 20 pound-feet of installation torque (same as the manifold screws - they're usually 19-21 pound-feet.) I like to use brass nuts, so they won't be stuck on next time. RENIX (1987-1990) manifold studs are threaded 3/8"-16, but I'm not sure about later versions. If you use never-seez, do not exceed 10 pound-feet of torque, and use a torque wrench!
 
Yeah, appreciate all of the advice. I talked w/ an old friend and he recommended the RTV copper too - didn't know it existed, but it was exactly what I was looking for. My problem seemed that the APN header wasn't quite at the exact angle that the stock manifold came in at. The seal just didn't seem to be as airtight. I put the copper RTV on along w/ the "donut" and all is well. I haven't been through a full tank yet, but honestly, don't know that I'm getting much better mileage. Just the thought of that makes me want to pull my hair out. It's basically a stock XJ - 2" BB w/ 235/75/15 (have to double check) tires - and am averaging 13.5 all city. That's before replacing the cracked manifold, '00 intake manifold, O2 sensor and new plugs, but I'll know shortly once I get done running this tank out if it's improving.
 
gone postal said:
Yeah, appreciate all of the advice. I talked w/ an old friend and he recommended the RTV copper too - didn't know it existed, but it was exactly what I was looking for. My problem seemed that the APN header wasn't quite at the exact angle that the stock manifold came in at. The seal just didn't seem to be as airtight. I put the copper RTV on along w/ the "donut" and all is well. I haven't been through a full tank yet, but honestly, don't know that I'm getting much better mileage. Just the thought of that makes me want to pull my hair out. It's basically a stock XJ - 2" BB w/ 235/75/15 (have to double check) tires - and am averaging 13.5 all city. That's before replacing the cracked manifold, '00 intake manifold, O2 sensor and new plugs, but I'll know shortly once I get done running this tank out if it's improving.

Use RTV copper for high temperature gaskets (like exhaust - works better than the red stuff) and for self-grounding sensors (coolant temperature sensors and the like.) It's actually impregnated with copper, so it doesn't insulate like the rest of the stuff does.

I only use two varieties of RTV - the black for general purpose, and the copper for the high-temp and self-grounding/electrical stuff. Makes no sense to have too much floating around, and the Loctite/Permatex stuff has all been "sensor safe" so far.

I like to keep my logistics simple. Got enough to keep in my hat as it is...
 
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