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OT: oxygen sensor thread direction

2

2x4

Well-known Member
replacing oxygen sensor Chevy 2500. New sensor has cut marks at the hex corners. I'm old school, so this was always an indication of left hand thread. I swear threads look right hand to me on the new one. Haven't taken old one out yet 'cause I'm wondering which direction I should turn it. Don't want to break anything off down there, nearly impossible to get a wrench on as it is, much less get in to drill out something broken. I've seen some other nuts marked like this but they were right hand thread instead of left hand. Something new going on? And any good tools to get in there besides an open end wrench? Crows foot on a rachet might fit.
 
You can buy a purpose-built O2 sensor socket at any auto parts store and that's what I'd recommend you use. I've not seen a left-hand thread on an O2 sensor and don't know why yours should have one, but anything is possible.
O2 sensor wrench
 
You could buy the replacement sensor and see what threads it has on it. Don't they make a special oxygen sensor socket that has a groove cut to let the witless hang out? Maybe someone knows.
 
Yeah, I can't imagine why they'd thread a sensor the other way. There has to be a pretty good reason to cut threads lefty -- axle bolt on left wheel, for example, so it doesn't tend to loosen as you drive.
 
I suspect that any left hand thread is designed for that purpose, ie some kind of turning axle where the turning action tends to loosen a right-hand thread. I can't imagine any reason for a sensor being a left hand thread. I bought one of those sensor sockets, only cost me about $12 at Princess Auto, our version of Harbor Freight up here in Canada.
 
Most likely right hand thread but if you want to be sure;
Hold it in your hand with your thumb nail in the threads, now rotate it clockwise and see if it is pulling it in toward your hand or pushing it away.
Pulling = right hand thread.
Pushing away = left hand thread.

As far as a wrench goes, if the sensor is in a real bad spot where a box end wrench will not easily fit, a purpose built sensor socket may not fit either.
 
Those make you life a lot easier. The other thing I've done is cut the top of the sensor off (its own special brand of misery) so I could use a regular 6 point socket. After years of heating and cooling in place they seldom come out "easy".
 
The only application I know of that used an LH thread O2 sensor was the RD side of the later-production ETD's.
 
(quoted from post at 11:27:55 09/08/17) The only application I know of that used an LH thread O2 sensor was the RD side of the later-production ETD's.
Click to expand...
ETD?
Eustachian Tube Dysfunction
End of Train Device
Elect the Dead
Electrothermal Deactivation
Electron Transfer Dissociation
Emotionally Transmitted Disease????????????
 
You should easily be able to tell just by looking at the threads ..... if your eyeballs are old just stick a fingernail into the thread and see which way it goes when you rotate the sensor.
 
> Essex Tri-Directional Tractor. Several hundred years ahead of its time.

Indeed, the ETD was one of the earliest machines to include a lambda sensor. Mounted just ahead of the turbo-compound supercharger, a left-hand thread was required due to the peculiar third-order harmonics of the ETD.
 
Any machinist could look at it and tell you. You should be able to do it too. Get out the reading glasses. Left hand seems highly unnecessary in that application.
 
should be an 18mm right hand thread. and, its also the same as a champion d-16 style spark plug, common to a lot of older farm tractors. an 02 sensor trick (old school) was to put a spark plug anti fouling cap on the 02 sensor to pass a bad cat thru emission testing. just a rumor i heard. yup, just a rumor.
 
Mark ..... no left hand threads were allowed north of the border ..... owners with anything with LHT's were sent to jail for a minimum of 3 months at hard labor. ETD's were not grandfathered and several owners are still incarcerated because the jailers enjoyed their company so much.
 
I tried that trick on a car with a failing catalytic converter. It simply did not work. In theory, it should, and on some vehicles it might work, but it did not work for the couple that I tried it on. Ended up replacing the cats.

The theory is that the sensor AFTER the cat should be switching at a slower rate than the one before the cat. Anti-foulers should slow down the switching. I wasn't that lucky.
 
They are definitely a right hand thread. Also, for some reason, it is recommended that you remove the sensor while it is still hot. This actually goes against everything I know about stainless steel, but it actually does work. Also use a generous amount of anti-seize lubricant. The use of a special oxygen sensor socket is also highly recommended. Using an open end wrench or a crow's foot could round off the hex - and they do round off fairly easily.
 
Hello 2x4,

Less then $10 at Harbor Freight. Lefty loose right tight!
Regular right hand thread,


Guido.
a171308.jpg
 
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