Question on O2 sensors...

I have recently purchased a 97 328i sedan and LOVE it. I am collecting parts to do a spring overhaul and I need to know how may O2 sensors I need. the car has 160K on it and I might as well do them all at once. Can you please let me know how many I need?

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This post was auto-generated based upon a question asked on our tech article page here: Pelican Technical Article: BMW 3 Series (E36) Oxygen Sensor Replacement

[Wayne 962]

"spring overhaul" - I thought you were talking about shocks and springs! The E36 six cylinder BMWs have four oxygen sensors, one before each catalytic converter on each side of the car. The first oxygen sensor meters the mixture coming out of the engine. The 2nd oxygen sensor is used to measure the effectiveness of the catalytic converter. If you wanted to save money, you might replace the two forward ones, and then leave the two rearward ones alone - if you don't have a check engine lamp, then they are working fine (as all they do is check the proper operation of the cats).

- Wayne

[bostogrun]

If the check engine light isnt on don't monkey with it. O2 sensors are like glass bottles there are either broken or not. Some people recommend changing them at 100k but I don't see the point in replacing a functioning part, especially when there is no safety issue involved. Years ago when I started working on cars I used to do things like that but over the years I have learned if it's not broke then don't fix it (except BMW Cooling Systems and related components). One time, I thought I would replace an O2 sensor on a 1992 525i just for preventative maintenance and it was so stuck in the cat that I wound up rounding off the hex on the sensor, so I had to drop the cat which required removing the mid pipe. I broke two rusty exhaust flange bolts and the mid to tail pipe clamp was so rusty I had to cut it off with a fly cutter. I went to an exhaust shop and had to pay a guy $100 to superheat the o2 sensor and twist the old one out when white hot. So much metal was removed from the bung that we did not think there would be enough thread left to hold the new sensor. It was loose and woobly. Thank God that it expanded enough to seal when it got hot. I almost had to buy a new cat which $500.

Well after all this, I thought at least my car is going to be set for a while but a week later the clutch went and I ending up selling the car for $900.