Cold or warm engine to change O2 sensor?

[mclasser]

I'll be changing the upstream O2 sensor before the cat converter in my Accord. Easily accessible but will it be easier to remove with a cold or warm engine? Is it like spark plugs where the engine should be cold?

 

[wallyuwl]

I just changed one in a similar location (different vehicle) and did it cold. Ended up using a breaker bar and it came loose easily. Would probably come out easier if it was a little warm, but I'm not keen on being around hot exhaust components.

 

[Trav]

With metals like iron and steel that have a similar expansion rate it doesn't matter much. Forget penetrating oil it doesn't do anything as it cant get past the seal.

 

[eljefino]

I had better luck after running a minute, from cold. I think the pipe expands faster than the "slug" of a sensor.

Go at it cold, though, as you might be surprised that they used anti-sieze at the factory. You can always run it and try again.

 

[Ga129]

I've done it both ways and couldn't tell a huge difference. Breaker bars are a wonderful thing!

But like the others said, try it cold. If you don't like it then run it a few minutes and try again. Exhaust components don't take long to warm up for the most part. Make sure you have an 02 sensor socket, those things are worth the money! And don't forget the anti-seize when putting the new sensor in. Good luck.

 

[Leo99]

In my very limited experience, the upstream O2 sensors came off easily but the downstream one I changed required a breaker bar and a pipe cheater bar.

Do you have the proper socket tools? I think it's 7/8"

 

[The_Eric]

Stone cold. Every one that I've ever had to do hot fought me. Many of them damaged the threads.

If it's easily accessed, put a 7/8" wrench on it and bash it with the ball of your hand. If after a half a dozen solid thumps (don't be ginger with it), it doesn't come loose, then try warming it up a bit.

 

[artificialist]

I couldn't tell the difference warm or cold. I never had to use anything to aid the removal or installation of the sensor, but because I never had to deal with road salt, so I don't know if this job becomes extremely difficult due to rust. Depending on how the sensor was located, either a 7/8 wrench or an O2S socket attached to breaker bar was all I needed.

If you do this job cold, and it gets difficult, you have the option of spraying PBblaster on the old sensor to make removal easier. Don't use it on the new sensor. Some new sensors leave the factory with anti-seize on the threads to make installation and future removal easier.

 

[oilboy123]

Don't let the anti-seize get on the O2 sensor tip. I try to do them warm, or cold. Not hot for obvious reasons.

 

[mclasser]

Update: Changed out the sensor today. Did it with the engine cold in the morning and the sensor came out easily. Applied a little bit of the provided anti-seize on the threads. The sensor didn't properly thread in by hand the first 2 times so upon putting it in & out of it's hole, a tiny dab of anti-seize got on the tip of the sensor. Used a paper towel to wipe it off. Hopefully it won't cause any issues and any residue will get burned up. Reset the CEL and hasn't come back after 50 miles of driving and several drive cycles.