Temperature Gauge Fluctuating

Rrusse11

Veteran Member
Joined
Jan 23, 2014
Location
PA Deutsch Country
TDI
2002 Golf, 5spd; 05 Jeep CRD
Intermittently my ECT gauge in the instrument cluster starts to "bounce" around. It falls from the 12 o'clock position of 190 to usually around 9 o'clock. It moves quickly and erratically, not at all smoothly. It never goes over the the 190 reading. Throttle pressure, ie, more diesel, tends to bring it back up.
This afternoon I hooked up the laptop with VCDS running and ran the ECT monitor function, and as a check, the ambient temp as well. The car warmed up with no problems, ECT1 gradually climbing to 85C, ECT2 was slower to change but after a half hour of driving, stabilized at 45C. This with an ambient of 13C.
Of course the car knew I was testing, so the dash gauge remained rock solid at it's 190F TDC setting. Prior to warming it up and driving, I removed the airbox and eventually located the temp sensor on the engine and jiggled the wires. I did not remove them, I've still not yet mastered how the bloody clips work! And with it's awkward position, thought I'd just try the jiggle first.
My research indicates that the sensor in question has 2 feeds, one to the gauge in the dash, and one to the ECU, guessing here that the problem is in the sensor, and not the thermostat itself.
Neither of the parts are particularly expensive, IDParts has both for my CJAA engine, and the sensor replacement shouldn't be a big job, though I'm a bit unclear as to how difficult the thermostat replacement is.
Any input or experience on this issue appreciated.
Cheers,
R*2
 

meerschm

Top Post Dawg
Joined
Apr 18, 2009
Location
Fairfax county VA
TDI
2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB
your thermostat, is not simple to replace.

the temperature sensor is read by the car's computer systems, which then set the dashboard indication. there is no direct connection from the sensor to the instrument panel. there is also a wide range of actual temperture readings which are presented as 190 to the driver so as not to alarm. (plus or minus almost 30 degrees)

(I would guess a wire is pinched someplace, but just a guess) depends on what kind of time you mean by erratic.

you may want to hook that VCDS up, and log a couple more drives, and wait for a session that shows the behavior, and then you will have some more data to inform.

I like to use engine controller, advanced measuring values, which will let you monitor and log a good number of parameters. HVAC controller may be worth a look too. it includes fan speeds as well as temperatures.
 
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Rrusse11

Veteran Member
Joined
Jan 23, 2014
Location
PA Deutsch Country
TDI
2002 Golf, 5spd; 05 Jeep CRD
Mike,
Thanks for the input. I too am suspicious of a faulty connection, the intermittent behavior is a bugger! My landline phone is doing the same thing when it rains, sheesh.
Just starting to learn my way around the VCDS, powerful tool, a lifetime to learn. Of course the car was on it's best behavior with the computer hooked up. My plan is to do what you've advised, try and get some data when the phenomena is occurring.
On erratic; the needle is moving smoothly, but will vary from 120 (7 o'clock) back to 190 in a second or so, quickly, this the most extreme event I've observed. Probably considerably faster than the mechanics of the thermostat would allow.
I've had some other problems with sensors and wiring so far, fingers crossed it's a similar issue, relatively ez and cheap to fix, just difficult to diagnose and isolate.
Thanks!
R*2
 

meerschm

Top Post Dawg
Joined
Apr 18, 2009
Location
Fairfax county VA
TDI
2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB




for reference, here are a couple graphs made using excel on the saved file. pretty much my ten mile drive to work first thing in the morning, after sitting all night. horizontal axis is samples, in this case about four per second. what you want to see is the knee on the coolant temp ( G62 I think) that shows transition from mostly closed thermostat to one in active regulation.

on the physical side, is your coolant level where it should be? does the color look right? does the heater work ok?
 
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Rrusse11

Veteran Member
Joined
Jan 23, 2014
Location
PA Deutsch Country
TDI
2002 Golf, 5spd; 05 Jeep CRD
Mike,
Coolant level is fine, heater's good. Thanks for the graphs, the aberrations on the thermostat/temps are clearly minor, nothing like the swings I'm getting on the gauge. Yesterday watching the temps it pretty much mirrors what the ECT1 was doing. A steady gradual increase till it hit operating temperature. ECT2 is I believe a sensor at the exit of the radiator, which was slower to rise, from ambient to an operational level of ~45C.
I'll play with VCDS some more, but increasingly I'm feeling it's a sensor
issue, and like you say, the sensor itself may be just fine, just a pinched wire somewhere.
Here's where I got the separate feeds from the sensor, one for the gauge on the dash, the other for the ECU. Both may be going to the ECU initially.
https://www.youtube.com/watch?v=eXNBlH0c4_U
Informative, and he seems to know what he's talking about.
Haven't managed to find anywhere in the VCDS software for a reading on the info fed to the gauge yet.
Cheers,
R*2
 

meerschm

Top Post Dawg
Joined
Apr 18, 2009
Location
Fairfax county VA
TDI
2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB
The U tube fella is looking at an older part. for a different engine.

I think you will find that the G62 temp sensor on your car only has two wires, and this single sensor is read by the engine computer, which can be queried by the VCDS to reveal the reading, and is also used as an input to the program which decides what to display on the instrument panel analog gauge.

http://www.amazon.com/Delphi-TS10278-Coolant-Temperature-Sensor/dp/B009EK5X1S/ref=sr_1_1?s=automotive&ie=UTF8&qid=1414771512&vehicle=2010-74-960-958-----12953------5-0&sr=1-1&ymm=2010%3Avolkswagen%3Ajetta&keywords=temperature+sensor
 

meerschm

Top Post Dawg
Joined
Apr 18, 2009
Location
Fairfax county VA
TDI
2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB
You are lucky you can read the second sensor on the radiator, my car will not share that info with me. it is used directly in fan control, but not shared on the data bus in a way the VCDS can access it.
 
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