volvo 850: Use heat to remove O2 sensor?

[JimBee]

I heated up the sensor lug pretty darn hot and the senor turned quite easily for 1/2 turn then stopped hard. More heat, then force turning got it a bit further, but again stopped hard after creaking metal sound.

Now my concern is if I do wrench it all the way out, wil the threads in the receiving lug be so messed up tht I can't get the new one threaded in? Then what? The whole pipe assembly has to come down—which I would like to avoid!

I'm using a long box wrench, so have pretty good leverage.

Suggestions?

[sitecore]

JimBee, heating up that stuck oxygen sensor is definitely the way to go to break through the rust. Just be careful not to overdo it or you could damage the surrounding components as you mentioned. I dealt with a similar stuck sensor on my old 850 during a heatwave last summer.

The extreme hot weather charge seem to multiply any binding issues like this. I found even after hitting it with some penetrant spray, the heat from the engine bay would cause it to seize up again quickly.

My trick was to try working on it first thing in the morning before temperatures rose. The cooler engine and metal seemed to help it turn more freely. I'd also recommend avoiding long heat soak times in traffic prior to working on it. Park it in the shade beforehand if you can.

Finally, have a new sensor ready to go in case it does get messed up. You're right about not wanting to damage the exhaust manifold threads. But heating carefully and using some temperature advantages from cooler mornings might just get that pesky original sensor out intact.

[abscate]

Once it starts to move flood it with PB Blaster or other elixir them work it back and forth. It will loosen up slowly

[foggydogg]

Since you got it to move, that made some space along the thread path for the juice. Apply a little heat, squirt it, and go back in a bit; you're just trying to get fluid to move down the incline. There is likely some carbon buildup on the exposed threads. A bit more juice, a bit more heat, a bit more time. Patience and persistence are your friends.

[JimBee]

Thanks all for encouraging words!
Gotta give it another go with more PB Blaster and a big dose of patience.

[erikv11]

You've got this now but I echo that time, penetrant and judiciously applied manual force are the keys now. You're basically out of the woods just need to bring it home.

Here are some more comments, granted this is splitting hairs but: You've already broken the threads loose, 1/2 turn is a huge movement, so more heat will have minimal additional effect. Heat works at the microscopic level to break the corrosion and that stage is completed (hooray!), you can make much bigger gains now with manual force. Even tapping it with a hammer to send vibration into the corrosion would probably be more useful than heat now but I wouldn't bother with that either unless back-and-forth isn't working. Main thing is work it gently back and forth with more penetrant seeping in there (what abscate said!). You're trying to pulverize the corrosion and clear that out of the thread channels. Giving the penetrant time to soak up/in/around can help agreed, that allows the penetrant to seep by capillary action into small spaces. Applying a little heat could help the penetrant wick into spaces within the now-fractured corrosion but since you have huge movement already, carefully turning the stuck sensor back and forth would be a far more productive way to get the penetrant working. Too much heat evaporates the penetrant which can be counter-productive.