Oxygen exhaust sensors

What does it sound like when an oxygen exhaust sensor goes bad? I had a real sucking (vacuum) sound coming from under the driver’s door, and now my mileage is really off. No light on the dashboard or anything…

If an O2 sensor goes bad it doesn’t sound like anything.

How is the car running?

It is running just fine, no roughness, no stalling…it’s just that my mileage has dropped off dramatically, and I can’t think of anything else that would cause the drop. Any ideas?

A very large number of things will affect your gas mileage. If you want anyone to start rattling off things that are of use then you need to provide a whole bunch of info.

  • What year is the CRV & how many miles are on it?
  • How are you determining that you gas mileage is off? (The only way is to use actual mileage driven divided by actual volume of gas burned).
  • When is the last time you: changed the air filter, fuel filter, spark plugs/wires, checked air pressure in tires, had an alignment, got new tires, had brakes checked etc.

If all maintenance things with the car are kept in order (rare) the first place to look for any sudden change - if it is real - is the tires and the cooling system (thermostat and coolant temp sensor).

Gas mileage always drops in the winter, btw - at least, if you live in a place that has winter.

It is a '97 with 141,000 miles on it. I keep track of the mileage per tank every time I fill up, and I have a little notebook with all the numbers ;)! I also stay up on the maintenance schedule for the car. (I’m really not that anal, even though it sounds like it on paper!) The tires were new last year and I just checked the inflation about a month ago. I never considered the thermostat, but that could be a likely culprit. It’s just that I want this little car to keep living as long as possible, and I’m thinking it is getting to the point where all the “little” things start going wrong! I also wanted to get some ideas before I go to the mechanic about what could be wrong and how much it will cost. But considering I haven’t had a payment for several years, I guess I could afford to put some into it now. Thank you for your suggestions!

Add a check for dragging brakes to the cooling system & tires.

Is the inside of the tailpie black with soot? (I mean reaaly,really black, almost like up the side of the car also) it is a sign of unburned gas, How far off is your mileage, winter is a time that it is normal for mileage to drop.

i’d say oldschool has the best place to start looking, thermostat or the temperature sensor, which will tell the computer the engine is cold and will pour more gas in than is needed; the easiest place to check would be the tailpipe, for black soot, the sign of a too rich mixture. everything else would run just fine with this condition.

sorry i failed to give cigroller credit for the temp sensor and thermostat. haven’t done a temp sensor in my '99 but it’s probably easier than the thermostat, and it will be cheap, this is a part that’s ok to get at autozone or whereever. i’d be tempted to just get one and put it in if you can find it under the hood.

My suggestion is to look for the source of the sound, as it sounds like more than coincidence.

I’m not worried about it in the least. Should you ever have cause you can edit your own posts (little pencil in the bottom corner).

I would test the temp sensor (just takes a couple minutes with an ohmmeter) before blindly changing it.

I recommend changing the thermostat every 4-5 years.
It’s convenient to change the coolant at the same time.

Have you had the following things done? Won’t affect MPG, but are good for long term health:
Transmission fluid/oil change.
Brake & clutch fluid change.
Valve lash adjustment.