Seized O2 Sensor

March 12, 2009 5:38 PM

I can't get the O2 sensor out of my car's engine, and I'm starting to round off the bolt!

I'm trying to replace the upstream O2 sensor in my 1998 Honda Civic LX. It sounded like a simple job, so of course something had to go wrong. The sensor is pretty well seized up. I'm using one of those special O2 sensor sockets with the big cutout to let the wires out. I'm pushing the thing so hard it feels like the walls of the socket are flexing a bit, and I'm starting to round off the bolt part of the O2 sensor. Things I've tried:

• Running the engine for a while first to get it hot.
• Striking the sensor (gently) with a hammer.
• Spraying it with WD 40 and giving it plenty of time to work its way in.
• Putting teflon tape around the bolt to help the socket get a better grip.

So, how do I get this stupid O2 sensor out? I don't want to destroy the old sensor (so I can put everything back the way it was, if something goes wrong), so I can't cut off parts of the sensor or drill anything out. Any suggestions?

posted by samw to travel & transportation (19 comments total)

Can you get a vise-grip on it?
posted by trinity8-director at 5:57 PM on March 12

I'm not sure what the O2 sensor looks like (i.e. is the nut attached to it? I'm no car mechanic), but usually with seized bolts, if penetrating lube like PB Blaster or heating it up with a blowtorch doesn't work, the next step is usually a nut splitter or cutting it off with a saw. If the non-invasive methods don't work, you might have to end up either leaving it in or getting a new sensor.
posted by Dr. Send at 5:57 PM on March 12 [1 favorite has favorites]

On preview, I recommend against the vice grip because that's pretty much guaranteed to round off the nut if it's as stuck as it is.
posted by Dr. Send at 5:57 PM on March 12

Take it to a local mechanic and offer them 20 bucks cash, paid then and there, to wrench it loose and then tighten it back down just enough to get you back to where you're doing the work.
posted by Science! at 5:59 PM on March 12

If your socket is flexing that is a problem contributing to the round off. Use either a 6 point box end wrench or sacrifice the current O₂ wire so you can use a solid 6 point socket. The socket lets you use snipe on a breaker bar in order to apply some serious torque.

Once you have a better tool, heat the exhaust pipe fitting with a torch before attempting to loosen the sensor.

Also if your sensor takes a 19mm socket a 3/4" socket is a smidge smaller. You can often pound a 3/4" socket on a slightly rounded fitting and get it out that way. This messes up the socket so I have a handy bucket full of cheap Chinese sockets just for this purpose.
posted by Mitheral at 6:07 PM on March 12

Hitting it with a hammer gently is about as useful as...not hitting it at all. *SMACK* that motherfucker. And use some PB - WD40 isn't nearly penetrating enough.
posted by notsnot at 6:07 PM on March 12

FWIW I am a mechanic....

WD40 isn't strong enough.... get a can of PB blaster and warm the engine to operating temp and then (with the engine off) soak it down. Let it penetrate and wait twenty minutes. Repeat twice. Then try to loosen again.
posted by peewinkle at 6:15 PM on March 12

that is, soak down the O2 sensor, not the engine.....
posted by peewinkle at 7:08 PM on March 12

My experience with vise-grips is that if they are really tight on the flats of the nut, they do not cause any rounding at all. (And once a nut is sufficiently rounded, vise-grips are the only thing short of a cold chisel that will get a grip on it.) So I would combine the PB advice with the vise-grip suggestion.
posted by bricoleur at 7:11 PM on March 12

Vice grips aren't going to get a better grip on a nut that can still take a socket.

What I had to do with mine was slip a closed end wrench over the old one and get it securely onto the nut of the sensor. At that point, of course, I had absolutely no way to get any torque on it. So I took my handy breaker bar (length of pipe) and placed it on the end of the wrench and gave it a good hard shove.

But if it's really as tightly on there as you say, I think the only way to get it off will be liberal, repeated doses of PB Blaster and possibly a propane torch on the bung to loosen it up.
posted by gjc at 7:39 PM on March 12

For reference, warming the thing with the engine is pretty much pointless - the point of heating something to loosen it is to do it quickly enough to allow some different rates of expansion to crack any corrosion/smegma/gunk/loctite/nastiness that is seizing up the threads. In the case of an O2 sensor it is most likely to be just corrosion, but even so you will need a blow torch to heat around the sensor to get anywhere with that technique. An engine warms up too slowly.

And do yourself a favour for next time and use anti-seize on it when you put the new one it.

Also, if it's buggered (which I'd assume) then there is no issue sacrificing the wire. Just cut it and commit. If you can, get a full socket or wrench on it and (after heating around the base) swing on it like you mean it. Watch your knuckles for when it does loosen off.

In addition, hitting it with a hammer is just making you feel better. It won't loosen up corroded threads one bit. It'll just damage the sensor or the exhaust pipe. If it was loose enough to be affected by hammer hits, you'd be able to overcome it with the torque from a split socket easily enough.
posted by Brockles at 8:10 PM on March 12

My experience with vise-grips is that if they are really tight on the flats of the nut, they do not cause any rounding at all.

I'd be fairly confident, if that was the case, that you've never used vice grips on something that wouldn't have come out easier with the right sized socket. Vice grips only work well when they deform the flats a little, and will always leave the hex worse off (unless they weren't really needed in the first place) afterwards. Stick to the proper tools first, use the vice grips if you've screwed the flats trying to gt it out.
posted by Brockles at 8:12 PM on March 12

Is there even the most remote of possibilities that it is reversed threaded? I know of at least twice where this situation has frustrated me . . .
posted by Neiltupper at 8:14 PM on March 12

Along with the tips here, make sure you put some anti-seize lube on the threads of the new one, it's worth it!
posted by ArgentCorvid at 9:54 PM on March 12

I was in the same spot as you several years back--overly aggressive banging, twisting and unscrewing had rounded the edges of the sensor bolt to a circle.

The only option at this point was to take my car to a mechanic, who sliced off the bolt head with a hacksaw. Of course, this caused the remainder of the bolt and sensor to fall into the exhaust manifold, which had to be removed from the engine and replaced. A day-long job for about $400 US.

The moral of the story is, if the edges of the bolt are beginning to wear down, take the car to the mechanic. Don't put yourself in my boat.
posted by Gordion Knott at 2:46 AM on March 13

Do not, do not, DO NOT hit it with a hammer. The end is ceramic and if you break it off you will be in a singular world of hurt.

Try the following:
1: Go buy a can of PB Blaster or Kryoil (only these two brands, they are far and away the best) soak it down good tonight and get a good night's sleep.
2:Tomorrow, get back underneath and soak it down again. Don't even bother trying to be neat about it coat that sucker. Using a new socket, with the longest handle extension (not socket extension, you want a longer level on the handle not to get the handle further away from the socket) you can fit on it, whale on the thing. If you still feel the need to swing a hammer, use it to hit the handle extension, not the bolt.
3: If it is still resisting you and taunting your abilities, get a propane torch and heat that sucker up until it's cherry red, I mean really glowing, it's on your exhaust, it can handle that kind of heat. Go drink a cool beverage and then come back and reattempt step number two.

I've worked on many old cars and this has never once failed to remove a bolt. Please be careful with the torch, and take the usual safety precautions because you will be torquing the everliving daylights of this thing and I'd hate for your car to fall on you.
posted by 1f2frfbf at 7:24 AM on March 13

WD40 is not a penetrating oil, it is not even a very good lubricant. It is best for moisture displacement. If you need penetrating oil go out and buy the real stuff
posted by Raybun at 7:24 AM on March 13

Bah, not enough coffee, I mean lever on the handle, not level.
posted by 1f2frfbf at 7:34 AM on March 13

a pipe wrench is the ultimate stuck-bolt remover. if you can get one on there, the more force you put on the lever, the tighter the grip gets. with a pipe wrench, the fastener will fail long before the wrenches grip does.

you will completely mangle the faces of the fastener, though.
posted by klanawa at 3:38 PM on March 14