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Would coolant leaking ONTO exhaust ruin O2 Sensor?
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SCM
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PostPosted: Fri Apr 15, 2011 8:53 am    Post subject: Would coolant leaking ONTO exhaust ruin O2 Sensor? Reply with quote

It seems strange to me that my O2 Sensor would go bad with only a few thousand miles on it. And it also seems like a big coincidence that it would go bad the day after I replaced my coolant expansion tank.

I still need to check the wiring coming from the sensor - but is it possible that coolant spraying out of the tank could have entered the exhaust through some leaks (I have at least 2 bad exhaust gaskets) and fouled the sensor?
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fastwagens
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PostPosted: Fri Apr 15, 2011 9:08 am    Post subject: Reply with quote

Chances are slim but you never know. The 4 wire u2 sensors have a heated element to burn off debris from the sensor but that came out after vans.
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PostPosted: Fri Apr 15, 2011 9:54 am    Post subject: Reply with quote

fastwagens wrote:
Chances are slim but you never know. The 4 wire u2 sensors have a heated element to burn off debris from the sensor but that came out after vans.


I thought the 4th wire was just a dedicated ground wire? 3 wire O2 sensors also have the heater, but there is no control over them in the vanagon other than on or off, AFAIK.

-Damon
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6984vwvanagon
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PostPosted: Fri Apr 15, 2011 10:27 am    Post subject: Reply with quote

For what it's worth Fords use Bosch O2 sensors, and
we have seen coolant contaminate them.
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PostPosted: Fri Apr 15, 2011 10:34 am    Post subject: Reply with quote

I'm curious as to why an O2 sensor would need a heater. It's hard to imagine that any 12v heating element could get the exposed element of the sensor hotter than the 1000+ degree environment that it is constantly bathed in.
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PostPosted: Fri Apr 15, 2011 11:10 am    Post subject: Reply with quote

At extended idle conditions with the O2 sensor fairly downstream from the mainfolds, it can cool off enough to be unresponsive (IIRC, activation temperature is around 600-650F). During extended idle, my exhaust is around the low 500s at the cat where my O2 sensor is located.

Also, when going down a long hill, the engine is just pumping cool air (shuts off the injectors) which will cool the sensor very quickly and will take some amount of time (not much) to get back to temp.

The heated sensor is just an optimization and not critical to function, but as emissions controls have tightened up over time, these optimizations have become increasingly necessary.
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PostPosted: Fri Apr 15, 2011 11:10 am    Post subject: Reply with quote

It is very common-

This is the only sensor that makes its own voltage. The voltage signal is proportional to the amount of unburned oxygen in the exhaust. When hot (at least 600. F), the zirconium dioxide element in the sensor's tip produces a voltage signal that varies according to the difference in oxygen content between exhaust and out side air .

They need reference air to work, taken from where the wires go in.

They need a heater to get working quicker.
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SCM
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PostPosted: Fri Apr 15, 2011 11:21 am    Post subject: Reply with quote

[quote="xoo00oox"]They need reference air to work, taken from where the wires go in.
[quote]

Does it sound reasonable that coolant could have dripped/sprayed onto the part where the reference air is taken in and messed something up?

I appreciate the insight folks are giving about why the sensors are heated etc but more importantly I'm trying to figure out if there's some reason (beside coincidence) that a new sensor would go bad simultaneously with a coolant leak from the expansion tank occuring and then being fixed.
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PostPosted: Fri Apr 15, 2011 11:23 am    Post subject: Reply with quote

6984vwvanagon wrote:
For what it's worth Fords use Bosch O2 sensors, and
we have seen coolant contaminate them.


Did it happen pretty quickly (in a few days) or was it after a longer period of contact with the coolant?
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PostPosted: Fri Apr 15, 2011 11:30 am    Post subject: Reply with quote

......if you have a wbx, your coolant tank is right above the O2 sensor. It is know to happen from oil or antifreeze leaking on them. It can happen right away.
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