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Hi all, I've got a '94 3vze A/T 4runner and I love this friggin car
Problem:
Like the title says, I've found 2 different exhaust leaks near the o2 sensor right before my cat converter. I found the leak by plugging a shop vac into the exhaust pipe and turning it to blow air.
Then I sprayed down my exhaust system with soapy water.
The first leak I found is between the o2 sensor gasket and the pipe. I was getting bubbles coming out between the gasket and pipe. The pipe flange is rusted and a bit crumbly, but not too bad. It is rusted and crumbly enough to cause a small leak though.
The second leak is actually on the studs that the o2 sensor clamps on to. I was getting bubbles that seemed like they were finding their way up the threads.
Things I tried to do to fix it already:
I replaced the o2 sensor gasket today and did a second leak check but bubbles were still coming out.
What are my options for fixing?
Any way to JB weld this leak or sealant it shut? Or is that going down a terrible path... Maybe something like this: https://www.permatex.com/products/ga.../?locale=en_us
Anyone know what the pipe is called or part number so I can find a replacement if that is my only option?
Is there some kind of thread paste I can put on the studs to close up the second leak?
Is it a new O2 sensor so you know it's a nice clean surface? If that's the case, you know the sensor-to-gasket interface is good, so you're just left with the gasket-to-flange interface to fix. Don't worry about the bolts -- they aren't there to seal anything, it's the flangeface-to-gasket you need to focus on.
1) Are you torquing the bolts to the correct value? And torquing them evenly rather than in a lopsided way?
2) Get that surface on the exhaust flange spotless clean. This is a plumbing problem and the gods reward those who make their joints clean.
3) If it still fails, with a new O2 sensor and new gasket and proper torque and cleaned up flange face (send us pictures, please), then *maybe* you could use the Permatex muffler cement. I've not tried it for gaskets like this, but they claim it works. This is what I've used: Permatex 80335 Muffler and Tailpipe Sealer, 3 oz. ($6 from Amazon). There might be better options out there as well.
No, it's an old o2 sensor - previous owner seems to have neglected this vehicle a bit. What you say makes sense - I will eliminate this potential leak source and grab a new o2 sensor from autozone.
(1) I am probably not torquing the bolts correctly but I have a torque wrench ordered on amazon and it will arrive in a few days so I will be sure to do that. However, I have a problem. I have absolutely no idea how to find torque specs in a reliable way. Right now I am at the mercy of Google images for diagrams but 9/10 I cannot find the torque specs for what I'm looking for. There must be a better way - I have the FSM from here: https://www.ether3al.com/runner90-95fsm/engine.html but there is nothing about torque specs. What manual do I need to find the torque specs?
(2) A little while after posting this I went back to check out the flange again, and the surface that meets the gasket is quite uneven especially in the middle there are two bump/ridges on either side. I will post a pic tomorrow. Feels like an uneven metal surface. Could this be caused by rust? It's like a bump, not a pocket, so idk if rust can do that. Can this be filed down? Do I need to be careful which grit file I use?
This isn't surprising to me; you just need it tight enough to keep it from backing off. There's very little load.
DO NOT use muffler cement or any type of sealant. You will never be able to remove the sensor after it reaches operating temp even one time. The thread stuff supplied with new O2 sensors is a thin compound mixed with tiny glass beads. As soon as it heats up the compound evaporates leaving only the glass beads.
If you have a rough mating surface on the sensor bung, it would be worth your while to clean it up. It's not easy to file "flat" by eye, so my first choice would be wet-or-dry sandpaper (wet) held onto something flat (a piece of wood would do). You're won't be able to go too fast sanding/filing steel, so you're not likely to over-do it.
Your method of finding the leaks is very clever. But why? Exhaust leaks are never good (even a small health hazard), but I can't imagine that size leak would produce a performance issue.
Thanks, I had a feeling muffler cement was a bad idea.
I think the issue might be due to the roughness of the mating surface. I'll get a file, some wet/dry sandpaper and a block from the hardware store.
As to why I am trying to fix this:
I am on a hunt for exhaust leaks because I get what sounds like an exhaust leak when revving the engine under loud (Idk why I can't hear the sound when revving the engine in idle) and I also smell exhaust fumes in the cabin.
Neither of these issues are so bad that it stops me from driving it but I'm curious about doing my own repairs.
I also have another exhaust leak the runs the length of the seam on the muffler which I will fix with muffler cement. Maybe you're right - the o2 sensor leak is minor compared to the muffler leak.
Ah! For what it's worth, I had an exhaust leak at each end of the cross-over. The gaskets had failed (after only 26 years! What kinda junk did they use?) You could hear it (I couldn't smell anything). To test, I took my magnet-on-a-stick and a washer, and used that to hold a small slip of paper as a tiny flag. Probing near the flange showed a fluttering flag which confirmed the leak (It's not easy to get your arm in there; too much very-hot stuff!)
The gaskets aren't expensive, and there isn't much to changing them, but getting to the six nuts is no picnic. If you do that, I'd suggest removing both front wheels (so you can reach in through the wheel wells.) Get a relatively short "gear-wrench" style ratcheting closed-end 12mm wrench (not much room for your regular ratchet.) Get 6 new "exhaust nuts." (Dorman has them at your local auto parts store, but they're not expensive from Toyota.) These nuts are technically one-time-use. Pick up 2-3 studs (again, Dorman has them) because after 25 years 1 or 2 of the studs will back out with the old nut.
Don't forget hearing protection. Not for you (you're not going to be using air wrenches anyway), but for any young ladies who might be within ear-shot while you're working.
02-20-2021, 06:19 PM
