N51 - oxygen sensors at 100k?

[02Pilot]

Is the general consensus that the N5x motors want new pre-cat O2 sensors around 100k miles? That was the interval I always used for earlier engines, and while thinking about the less-than-stellar MPG I'm getting in my 128i it occurred to me that at 116k miles I think I'm still on the originals. Before I order I just wanted to confirm that my assumption still holds as a valid maintenance interval for these motors.

[MarcoZandrini]

100k miles is the consensus here. Sensors get lazy as they age, and tend to under-report the O2 levels.

[bmwdirtracer]

Certainly, my friend, I agree that primary O2 sensors are getting old and slow, by 100k miles. That's the mileage interval at which I think they're due.

That said, I have another view: If it ain't broke, don't fix it.

Spark plugs, oil changes, valve cover gaskets, cam gear bolts, and the tensioner pulley are on my list of "watch out for", on your engine.

I'd put the O2 sensors on the list immediately as soon as you see a fuel trim issue.

Until then, save your money.

My 2 cents.

[jclausen]

I agree, also the o2 sensors are monitored by the check engine light system. I replaced mine doing pre cats first then post car sensors I saw no improvement in mpg. So there are certainly other repairs that will be needed, save your money for those.

[02Pilot]

So wait for a fuel trim fault to be set, then replace? Or should I be digging in to monitor the live data and replace if I see something odd?

[bmwdirtracer]

Watching live data never hurts....

It would seem that fuel economy figures are the factor which causes your concern. What kind of numbers are we talking about?

[02Pilot]

Nothing terrible. EPA is 18/28, and I'm probably right around there. I used to routinely beat the EPA estimates in my 525i, but in this car I can't seem to do it. Just a little surprised I can't, I suppose. Maybe I'm enjoying the loud pedal too much.