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Old November 20th, 2006, 17:12   #1
Greentone
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Default Coolant Temp Sensor Replacement

My coolant sensor needs to be replaced in my 04'Jetta. Instead of paying 140.00 to get it installed I purchased one from the dealer for $30.00 and hope to install it myself. This website has been a help in the past but I can't find any instructions on how to replace the coolant sensor. It's to dark out to look under the hood today but I'll be attempting to do this tomorrow. I'm looking for advice, point me in the right direction please I have no idea what I'm doing or where this sensor goes.
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Old November 20th, 2006, 20:49   #2
tkindler
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Remove the engine cover and on the driver's end of the engine, look for a part with three plugs sprouting from the top as in this picture:

http://pics.tdiclub.com/showphoto.ph...0&ppuser=16933

On the back side toward the bottom of this part is the coolant temperature sensor. It has an electrical connection with a wire coming from the back side of it. It is held in place by a little plastic clip which can be pulled off toward the bottom of the sensor. Be gentle, the clip can break, and if you drop it, have fun looking for it. You will need it to secure the new sensor. Some folks suggest having a replacement available, just in case. The steps I followed when I replaced mine are as follows:

0. It is best to do this while the engine is cold.
1. Open the top of the coolant overflow container to relieve pressure.
1a. You will probably want to remove the large hose running from the airbox to engine. This will make access to the sensor easier.
2. Remove the electrical connection from the old sensor
3. Connect electrical connection to the new sensor, so if I drop it, it doesn't get lost.
4. Remove the retaining clip holding the sensor in place
5. Be sure you have the new rubber O-ring on the new sensor
5a.Remove the old sensor, being prepared for coolant to come out.
5b.Pull and twist the sensor, it should come out fairly easily.
5c.Check to be sure the rubber O-Ring came out with the old sensor
6. Quickly insert the new sensor with the new O-ring to prevent coolant from leaking
7. Re-attach the plastic clip to secure the sensor.
8. Check coolant level and, if necessary, top up with the recommended mixture of G12 coolant and distilled water. I used 50/50, although I don't think that is the exact recommendation. If you don't have G12 coolant use distilled water only.
9. Put top back on coolant overflow container.
10 Re-attach any other parts you removed.

Note: Yours is a PD engine, mine is an ALH, but I think all this applies to your engine. Someone else chime in if I am mistaken.

Last edited by tkindler; November 20th, 2006 at 21:12.
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Old November 20th, 2006, 20:53   #3
whitedog
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tk, I have two questions.

One is do you twist the sensor because that is part of the lock or is that just to break it loose?

Secondly, can you pull out the old sensor enough to see the o-ring is on before the coolant starts to flow?
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Old November 20th, 2006, 21:14   #4
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Well, I ain't that fast (old and slow) and invariably the O ring doesn't come out, so I use an alternate method.

I use an 18 inch piece of clear tubing of the appropriate size. Clean the drain nipple, attach tubing and route to empty gallon milk jug. Open the drain and fill the jug. Close drain, pull the tubing, and cap the jug.

Now change your temp sensor at your leisure. No spillage. Pour the coolant back in.
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Old November 20th, 2006, 21:21   #5
tkindler
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WD - Once the clip is removed there is no other locking mechanism. I just jiggled and twisted a bit to break it loose.

I didn't really take time to check. Since the cooland was cold and not under pressure, I didn't loose much anyway.

Paramedick - I like your approach. No need to rush.
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Old November 21st, 2006, 11:03   #6
JayT
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my two cents since I too read on here how to change sensor. I'd go for an alternative to pulling out the sensor and then putting the new one in. The new one did not go in so easy and I lost alot of fluid then I had to go to VW and get some g12 coolant, which they only had in gallon size, so cost me an extra 20 for repair.

Having said that, its awesome that this forum is around to help up defer some cost by doing work ourselves.

jt
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Old November 21st, 2006, 17:23   #7
Greentone
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Thanks for all the info everybody. Got the sensor switched today and my car is running better than ever.My engine was getting flooded because of the bad sensor. Not any more!
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Old November 22nd, 2006, 06:59   #8
REBEL TDI
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Quote:
Originally Posted by Greentone
Thanks for all the info everybody. Got the sensor switched today and my car is running better than ever.My engine was getting flooded because of the bad sensor. Not any more!
Just out of morbid curiosity, how long did it take you? I'm kind of slow myself when I work on the car. That's a project I have scheduled for tomorrow as well as replacing the vacuum lines if I can find them this afternoon after work.
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Old November 22nd, 2006, 09:58   #9
McBrew
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For those who need to do this job, you can often find a new coolant sensor for around $18 at TDIparts.com. I picked up a few at Impex on sale for $5 each.
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Old November 26th, 2006, 06:44   #10
REBEL TDI
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From the picture you have and looking under the hood of my car; isn't it behind those three plugs in the picture? Like facing the firewall? I haven't had the time to replace mine yet.
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Old November 27th, 2006, 13:17   #11
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I attempted doing the quick swap method and although the old black sensor came out quite readily, the new green one was not easily inserted. In my
rush to stop losing fluid, I ended up cutting the o-ring while pushing it in.

Did not realize the o-ring was cut and since there was fluid all over, I did
not notice it was leaking. Took the car for a short spin and just before
pulling in the driveway the coolant light began blinking.

Pulled out the sensor the next morning - had to let it cool - it was hot. I
let the coolant spill slowly into a small yogurt cup placed under the sensor and sucked it up as it filled with a turkey baster into a larger container.
Once it had cooled I pulled out the sensor and saw the damaged o-ring.
Went to dealer this morning and got a new o-ring and some G-12 and
put it back together the right way and filled with 50/50 G-12/Distilled water.

Appears to be fine. If you want to do this and not have to worry about rushing or screwing up, drain some coolant first - either from the drain nipple, or from the sensor.
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Old November 27th, 2006, 21:39   #12
vigog
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Yes REBEL the sensor is behind and slightly below the plugs.

The job took me about 10 min.

One thing that is helpful is to practice taking the connector off the temp sensor by taking a connector of in a more accessible location such as the MAF sensor which has the same type of connector just bigger.

It is suggested that you wash down the engine if you do spill any coolant

Here is a good how to..... http://www.inmud.co.uk/page27.htm
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Old November 28th, 2006, 20:34   #13
Eudaemonic
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Thanks for the write-up! Nice to read about this as I have to do mine soon.

Quick question though. NutnBolt mentioned something about an old black sensor and a new green one. Is the green one an new/updated version? Someone else told me about it, saying the black one is cheaper. But is the green one better?

Another quick one. I'm used to the old mkIIs. Are there 2 CTS (one for the ECU and one for the instrument cluster like in the good old days, or only one CTS for both?

Thanks
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Old November 28th, 2006, 20:54   #14
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Quote:
Originally Posted by vigog
One thing that is helpful is to practice taking the connector off the temp sensor by taking a connector of in a more accessible location such as the MAF sensor which has the same type of connector just bigger.
That's a great idea. The connectors on these cars are impressively well designed, but they're often smarter than I am... figuring out how to release the latch mechanism -- especially if the connector in question is shoulder-deep in the engine bay -- is often the hardest part of the job.

Maybe How-To's that include the words "just unplug the XX connector" should include "the XX is similar in style to the YY connector"...

Eddy

p.s. Eudaemonic -- two sensors, one housing.
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Old November 29th, 2006, 05:52   #15
mparker326
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Quote:
Originally Posted by Eudaemonic
Quick question though. NutnBolt mentioned something about an old black sensor and a new green one. Is the green one an new/updated version?
Yes, the green one replaced the black one. AFAIK, you can only buy Green and Blue sensors. Most cars take the Green and a few older model cars take the Blue.

Quote:
Originally Posted by EddyKilowatt
figuring out how to release the latch mechanism -- especially if the connector in question is shoulder-deep in the engine bay -- is often the hardest part of the job.
That is where mirrors come in handy. Even if you know how to take it off, it is a pain if you can't see it since VW loves to place things upside down.
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Last edited by mparker326; November 29th, 2006 at 05:54.
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