Somewhere in searching the Net, I remember seeing a picture (actually several of them together) showing various discolorations of the oxygen sensor and the cause for each one. Anyone know where to find such a graphic illustration of discoloration and cause?

 

I just bought a new one today because of the CEL on almost all the time and one of the ECU's error codes pointing at the O2 sensor. I removed the old one and its tip has carbon black around the base (too rich) but the rest of the tip is coated white. It is pretty well baked on and takes quite a bit of scratching to remove some. Is the white discoloration indicative of a coolant leak? Or is white the normal discoloration?

That sounds fairly normal.

I will be changing mine this weekend, and will let you know.

Could it be ash from burning oil or gas additives?

OK, I used ramps and after 2 trips to auto parts stores for sensor wrench (only compact one with offset worked) and liberal application of CRC 6-56 I got it off. It was very easy to unscrew once I had access and grip. 40000 miles on it and changed in desperate attempt to improve MPG. The sensor is soothy but no deposits whatsoever.

Vanguard,

Is this what you are looking for:

http://www.ngkspark.com.au/tech_index.htm?http://www.ngkspark.com.au/pages/tech_info_oxygen_sensors_index.htm

The pictures are toward the bottom of the page

Jacek

Vanguard,

Is this what you are looking for:

http://www.ngkspark.com.au/tech_index.htm?http://www.ngkspark.com.au/pages/tech_info_oxygen_sensors_index.htm

The pictures are toward the bottom of the page

Jacek

It wasn't the page that I found before but thanks for finding one that shows the deposits and what causes them. Mine had a white coating on it and, according to that web page, it is either additives or burning oil. I don't see any blue flumes coming out the tailpipe, and since the O2 sensor has 130K on it then it is probably additives. It had some very high mileage on that sensor so I'll inspect it next time when I replace it sooner (like around 40-60K miles).