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2000 Passat GLS B5 1.8T FWD wagon
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Discussion Starter · #1 ·
I have a 2000 Passat GLS wagon, ATW 1.8T w/ Tip, 165k. Started getting the traditional "Varies Widely" coolant temp gage behavior last week. I plugged in my code scanner just for fun a few different times to see what was going on. My scanner lists two coolant temps, which would sometimes show two very different values - the first one seems to be the "right" one (around 190 F), and the second one would sometimes be close but often would be reading much lower (130's or so). Sometimes my cluster gage even agreed with one of them!

sample data, taken in the driveway after a drive:

coolant temps_resize.jpg

So I read the posts here and checked the links, got myself a VW replacement sensor (the green one) and oring, and did the job yesterday. Not too bad - about an hour or two for that plus replacing the cracked reservoir.

Now the temp behavior is consistent - the 1st scanner reading matches the cluster gage within +/-5 degrees or so, and the 2nd scanner reading is around 130 or so.

Are there two coolant temp sensors??

I searched the forums and the Bentley manual; only other thing I could find was the radiator fan thermo switch in the bottom of the radiator.

So I am wondering if the two different temp readings means I still have a problem....I hope I don't have to start crying. :cry:

Thanks for any advice you can offer!

- Dave
 

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There is only one CTS but it has 2 elements, one feeds the gauge and the other feeds the ECU. They measure the coolant at the same place so should be about the same.

There are a few other temp sensors, maybe your second reading is one of those.

Scan the car and post the codes.
 

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2000 Passat GLS B5 1.8T FWD wagon
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Discussion Starter · #3 ·
Thanks for the info!

No fault codes, according to my Actron reader....I guess everything's OK?

Tried a different test today - started it from cold and just let it idle up to temp in the driveway. Again, the 1st scanner temp follows the cluster gage temp closely. The 2nd scanner temp stayed a few degrees above the IAT, which started in the low 90's and went up to around 100 by the time the cluster gage reached 190. It's in the 80's outside and my car's been in the sun all day, so these temps all seem to make sense. I suppose the 2nd coolant temp could be from the fan switch sensor, but the Bently book lists on/off ranges for that switch that make it sound like it is just that - an on/off switch, not a sensor with continuous output.

If that 2nd temp really is coming from another sensor, I don't really need to know what it's measuring (I'm just curious).

But if both scanner temps are coming from the same ECT sensor and are supposed to providing the same signal to 2 different places, then I'm concerned I have a wiring problem, because the two readings are so far apart. This would be the part where I start crying.

- Dave
 
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