Bad O2 = Overheat?

Sounds like my O2 sensor might be bad. I'm in Chicago at the moment, so I can't test it for 2 days, but I'm wondering if a bad O2 sensor might be one of the causes of my overheating. Any ideas? If the o2 sensor is bad, then the ECU would seem to do some screwey mixtures to compensate for it, but I really don't know.

Are you saying overheating as in coolant temps get too high? I can't see a faulty O2 sensor would do that. Our cooling system should be capable of cooling the car when it is running at WOT for good chunks of time. If you are driving around at part throttle all the time (I presume you are if your coolant temp gauge keeps creeping up), you will be at reduced engine load and your cooling system won't have to work as hard as it does at WOT.

I would look elsewhere for your overheating problem.

I thought the ECU might read the mixture as being incredibly rich from the lack of O2 sensor and lean it out or something, possibly causing flash overheating from incredibly rich mixtures.

But, I think you're probably right. Thanks.

when an o2 sensor goes out it usually won't change voltage at all which will cause the ecu to stay in open loop it shouldn't make you engine over heat. whens the last time you replaced your radiator cap? pressure on a liquid raises the boiling point so if there is even a small leak in the system it can cause you to over heat. i would replace the radiator cap and pressure test your coolant system. my 185 was doing the same thing and it was just the cap.

No, it's definitely not that. Look at my post history for the past month, or at least the like 10 threads on the turbo performance section by me for the huge problem.

:wink: If its overheating in the water cooling side then try to remove the water sensor valve you will find that on the block under the aulternator, you will need to remove 2X nuts and hose that goes to bottom of radeator, once remover there is what looks like a silver round thing with a spring in the middle, once out to test it simply boil the jug for a coffee and wile u drink your coffee put some boiling water into a cup ( glass is better ) drop your water thermistat into hot water to see if the spring moves thus opening the valve, if it opens then its ok, but if it does not open then thats the overheating prob, i know this because i have killed a head from the faulty water thermistat, its a motor killer ....

CodingParadox":e6khu9od said:

Sounds like my O2 sensor might be bad. I'm in Chicago at the moment, so I can't test it for 2 days, but I'm wondering if a bad O2 sensor might be one of the causes of my overheating. Any ideas? If the o2 sensor is bad, then the ECU would seem to do some screwey mixtures to compensate for it, but I really don't know.

Click to expand...

As brophats has stated, if your 02 sensor goes bad then you will be stuck in open loop mode and run rich. The sensor is very basic it pretty much reads a 1 or 0 and sends it to the ecu. When it breaks there will be no voltage to the ecu and the comp will see 0s all day long and keep you on the rich side. To confirm, unplug the 02 and drive around after you've warmed up the car. With no 02 sensor you will ensure that you are stuck in open loop mode and if your car still tends to over heat you know that running lean from bad 02 sensor signals was not your problem. I'd check for themostat issues or air in your cooling system. Also besure you're not loosing any coolant and that your level doesn't drop. That could indicate a HG or other coolant leak somewhere.

If the O2 sensor fails, the ECU will use a saved voltage
and continue running. It will richen up the fueling
and reduce mileage.

You can check the O2 sensor at the check connector,
or at the ECU. Just look for 0-1v with an VOM.

Read all about the o2 sensor at http://www.autoshop101.com/
> tech articles
> 37 Sensors#6 - Oxygen / Air Fuel Sensors w/ques.pdf file size 328KB

58 Emission#4 - Closed Loop Feedback Systems.pdf file size 233KB

There are several conditions that the ECU will switch
to open loop, not just a bad O2 sensor.

I had a bad O2 sensor for a while.
That in it self would Not cause overheating.

Regards;