When should you consider changing out your O2 sensors? I'm not getting any codes but my gas mileage is down to around 21-22 mpg from around 24-25 mpg when I first got the car (Brand new). Now, the car has 125k on it and am just wondering if it's about time to change out the O2 sensors to get the extra mileage back. Figure if it'll come back the O2 sensor will pay for itself in a few tanks anyway.

I realize there's a ton of other things that could be lowering the mileage but with 125k on the clock and that I run fuel cleaners though every 5-10k that the factory sensors maybe on their way out and worth replacing?

 

As you said, there are other factors in fuel mileage. And since it is just a couple mpg different than when you got the car, i wouldn't blame the sensor just yet.

If you run the fuel system cleaner through your car then that part of your car is probably good.

When was the last time you changed your air filter? That may affect your fuel economy.

Make sure your tires are properly inflated.

Also one thing to consider is that as the amount of miles on the engine increase, carbon buildup inside and seals wearing out are going to affect your performance and fuel mileage. Your performance may actually increase, but you may start to lose efficiency.

P.S. I personally do not change O2 sensors until I get a code telling me there is a failure in the O2 circuit; or if I am installing a wideband for tuning.

 

Estimated lambda sensor life from Denso: 55-65k

 

start with changing your oil, spark plugs, and air filter. o2's are kind of expensive.

 

Air Filter: AEM cold air filter (K&N) reprimed 10k ago
Spark Plugs: NGK coppers, replaced every 10k
Cap & Rotor: Replaced with OEM every 20k
Spark Plug wires: Checked resistance to be well within spec (125k on the wires)
Oil: Mobil1 5w30 replaced every 10k (oil lab tested to be fine @ 10k interval)
Fuel: Regane run though the system every 5-10k (more like 10k now, every oil change)
Tires: 32-38 psi all the time depending upon how hard I want to ride at.

If it's a carbon buildup issue would you recommend water misting the engine then? Haven't done that recently (maybe did it once before) but steam cleaning the combustion chamber would probably help though I'd think that the Regane would help prevent along with the synthetic oil the carbon build up down.

So it's not really an issue with maintenance since I'm keeping up with it. If the lifespan of the O2 sensor is less than 80-100k I'm guessing I could pick up a few MPG with a new one? I can buy a Denso OEM replacement for $40 so it's not that expensive. Just wondering if it's one of those things that just should be replaced every 100k or so esp considering that most of the maintenance stuff is kept up with.

 

Wow I really don't know. Those 3 things have just worked for me in the past. I suppose you could give the o2 sensor a shot. Maybe wait for some other replies if you're not keen on spending too much money.

 

O2 sensors have a service life - they're meant to be replaced. They only last 75-90k miles until replacement is usually needed. I'm not saying that they just die and a code will be thrown...but they begin to get lazy in response and so your gas mileage (and idle sometimes) will be effected.

Don't get a Bosch O2 for Honda/Acura and also don't get a 'univeral' one where it doesn't come with the factory connector and you're required to solder/crimp on the old one.

 

I'm looking at a OE Denso sensor that's $40 from sparkplugs.com