Not that I'm looking for something (anything!) to do in the time of COVID...

I've got 135k miles. Original upstream O2 sensors. No codes. Runs great.
Should I think about replacing them while I have some time, or wait until
they go demonstrably bad?

Thank you.

 

If you don't mind spending the money on them and have free time then yes replace them.

All O2 sensors start getting pretty lazy by 100k miles, the typically live a very very very long life and die INCREDIBLY slowly, sometimes actually outliving the engine they were originally installed on.

However that doesn't mean they're actually GOOD, it just means they weren't bad enough to toss a code, they were still cycling but as they keep building up deposits over the miles they start to get EXTREMELY slow to react to changes.

Just my butt dyno estimate, the actual life of an O2 sensor to quickly respond to fuel changes is probably closer to about 80k miles, after that it just keeps getting slower and slower and slower to react.

 

Great advice. Thank you!

 

OK. Couldn't get the bugger out by force and penetrating oil. Dropped the cat and
went for the OA torch. When it finally moved it took the bung with it! Hey, it's out.

Do I need a whole new exhaust manifold or is it possible to find someone with the TIG
talent to weld on a new bung?

Oh, and that's just the left side.

 

I read this and decided to swap both upstream and downstream in both banks with Denso's. No codes but at 150K methinks it's time (noticed a 3-4 mpg mileage drop, slight hesitation and rough idle that improved somewhat with throttle body cleaning but still not where it should be). Some of them are PITA to get to so may decide to offload them to my mechanic (he needs the work as with COVID things have been slow for him).