Thermostat Replacement

irbk

Veteran Member
Joined
May 27, 2008
Location
WI
TDI
04 Jetta GLS TDI
My CEL is on and DuPage AutoWerks diagnosed as a bad thermostat. They replaced it but a few days later the CEL came right back on (according to them, it takes a few days for the thermostat to kick in, thus why the CEL was off for a few days and then came back on) they think the replacment they installed was faulty. I don't live anywhere near them so they refunded my $$. There isn't a "trusted TDI guru" close to me and I've seen threads saying that replacing the thermostat is easy. I'm not inclined to try it myself, however if it's so easy, would just some one like Midas be able to replace it for me? I've got an appointment with Small Car Motors in Zion (recomended by a fellow TDI'er that has had good luck with the place) however they are 45 min south of home. Long story short, it would be SO much simpler to take it to the Midas that's about a mile up the street from work (that I never had any problems with when I took my gasser there) then to have to drive 45 min south of home (and home is 60 min south of work) to get the thermostat replaced.

Thanks in advance.
 
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n1das

TDIClub Enthusiast, Veteran Member
Joined
Jun 11, 2002
Location
Nashua, NH, USA
TDI
2014 BMW 535xd ///M-Sport, 2012 BMW X5 Xdrive35d, former 3x TDI owner
The original thermostat most likely did NOT need to be replaced. The new thermostat that's in there now likely does not need to be replaced either.

Most often the intermittent behavior triggering the CEL is due to a failing coolant temp sensor (CTS). They are cheap and easy to replace and it's not hard to change it yourself. The CTS is a common failure item...had it happen to me too...a new CTS fixed it and I changed it myself. I'm still on my original t-stat at "only" 296k miles in my 02 Golf TDI.

The CTS actually has TWO sensors inside the sensor body and there are 4 connections on the sensor. One pair of connections goes to the ECU and the other pair goes to the instrument cluster. Usually the sensor goes intermittent before it fails completely. If it's the sensor going to the ECU, that can give intermittent temp readings and/or codes. If it's the sensor going to the instrument cluster, you'll see it as intermittent low temp readings when you know the coolant temp is at normal operating temp (190F). Sometimes they both go intermittent and you'll have intemittent/erratic temp reading and CEL codes. It also could be simply that the connections at the sensor just need to have their contacts cleaned with a contact cleaner/deoxidizer spray and nothing needs to be replaced.

There is a coolant temp sensor replacement "how to" procedure posted somewhere on this site. (Use SEARCH!)

That shop isn't doing you any favors either. The thermostat doesn't "take a few days to kick in". It does its thing every time the engine is run enough to warm it to operating temperature (190F). The thermostat IS what regulates the cooling system to maintain a 190F operating temp EVERY time you drive the car.

Good luck.
 
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HopefulFred

Veteran Member
Joined
Sep 5, 2002
Location
Atlanta, GA
TDI
Golf, 2006, Indigo Blue
David is right, I feel sure.

There was a recall for a lot of those sensors. You may want to check to see if yours can be replaced for free.
 

irbk

Veteran Member
Joined
May 27, 2008
Location
WI
TDI
04 Jetta GLS TDI
Well, if the shop is lying to me about the sensor taking a few days to kick in, then "DuPage AutoWerks" needs to be removed from the list of trusted places.
As for it being the sensor, that was my original thought, however after taking it to DuPage, because they are a "trusted shop", they told me that it was the thermostat, not the sensor.
Again, I ask my original question, if it's such an easy replacment, do I need to worry about taking it to a TDI place that's way out of my way or should I be just fine taking it to the Midas up the street.
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
irbk said:
Again, I ask my original question, if it's such an easy replacment, do I need to worry about taking it to a TDI place that's way out of my way or should I be just fine taking it to the Midas up the street.
I'd do it myself - it really isn't very difficult. You'll just need to have some additional coolant available since you will loose some.
 

irbk

Veteran Member
Joined
May 27, 2008
Location
WI
TDI
04 Jetta GLS TDI
Problem is if it's not the sensor (and DuPage says it's the thermostat, not the sensor) I'd rather have some one working on it that can fix the problem (whatever it is) and clear the CEL.
 

greengeeker

Vendor
Joined
Feb 8, 2006
Location
Cambridge, MN
TDI
2002 Jetta GLS
How far are you from Madison? Give jasontdi a call if you need help.

I would advise against taking it to the midas down the street - they're likely to replace the lost coolant with the green stuff.
 

irbk

Veteran Member
Joined
May 27, 2008
Location
WI
TDI
04 Jetta GLS TDI
Very, very, very far. JasonTDI is at least a 2 to 2.5 hr drive. Much closer to go to Small Car Motors in Zion, IL
they're likely to replace the lost coolant with the green stuff
Ahhh, I take it the TDI has a different kind of coolant? (showing how TDI illiterate I am, and further proving how I'd rather have some one who knows what they are doing fix it!)
 
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validius

Lacking in ZDDP
Joined
Oct 9, 2006
Location
Grand Rapids, Michigan
TDI
1997 GTI TDI
irbk said:
Very, very, very far. JasonTDI is at least a 2 to 2.5 hr drive. Much closer to go to Small Car Motors in Zion, IL Ahhh, I take it the TDI has a different kind of coolant? (showing how TDI illiterate I am, and further proving how I'd rather have some one who knows what they are doing fix it!)
2 hours is nothing to see a guru like Jason. Just drive out there. its worth the drive to have a car that works.
 

validius

Lacking in ZDDP
Joined
Oct 9, 2006
Location
Grand Rapids, Michigan
TDI
1997 GTI TDI
irbk said:
Ahhh, I take it the TDI has a different kind of coolant? (showing how TDI illiterate I am, and further proving how I'd rather have some one who knows what they are doing fix it!)
Compare that 2 hour drive to the $6000 new engine you will need after they mix green coolant with G12.
 
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Lefty

Veteran Member
Joined
Oct 21, 2005
Location
Lazear,Colorado Population 60
TDI
Jetta, 2000,Green GLS
Make the trip to jasontdi a mini vacation. Look for a few places to visit in his area of interest and enjoy it while you have your car fixed the right way.

And remember what has been stated. The regular coolant is not for our cars, it will ruin it if Midas puts it in and you will have a much bigger bill. Our cars use G12 Coolant.
 

irbk

Veteran Member
Joined
May 27, 2008
Location
WI
TDI
04 Jetta GLS TDI
Yeah, I'll go to either JasonTDI or Miks for the timing belt that's coming up in about 6 months (depends on who's available). For this though, I'll trust Small Car Motors. My buddy takes his TDI there and has never had any problems with them. Plus, while it's a pain in the butt to get the car there, I can get it there, it's just 45 min out of my way.
 

irbk

Veteran Member
Joined
May 27, 2008
Location
WI
TDI
04 Jetta GLS TDI
Just wanted to say thanks to everyone for your posts! I do appreshate it!!!
 
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