A4 thermostat change How-To

JB05

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Il.USA
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The BEW T-stat can be a bit more tricky than this ALH type. I had lots of trouble trying to get the bottom bolt off the flange due to the tight space behind the alternator. Also the flange on the BEW has a 45 degree bend which makes it more difficult to hook onto the t-stat if you want to go that route.
 

paramedick

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Versailles, Kentucky
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2015 Audi Q5 TDI
The BEW T-stat can be a bit more tricky than this ALH type. I had lots of trouble trying to get the bottom bolt off the flange due to the tight space behind the alternator. Also the flange on the BEW has a 45 degree bend which makes it more difficult to hook onto the t-stat if you want to go that route.
Just did one. Easier to pull the alternator and serp tensioner than fight that bottom bolt. Adds ~ 15 minutes to the job.

If your BEW doesn't have the drain at the lower radiator hose, you will lost a LOT more coolant than the 2003 or less A4 cars.
 

PDJetta

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'04 Jetta GLS TDI Pumpe Duce Platinum Grey w/ Leather
Thanks for the tip Paramedick. I'm replacing the termostat in my BEW next weekend. I'll remove the alternator first, which is not bad on the BEW. That will probably better my chance of getting the O-ring in the right place too. I have a new thermostat housing on order too (it's specific to the BEW). I'm lucky, mine has a radiator drain. I guess whether or not a drain is present depends on where VW sourced the radiators from.

--Nate
 

mdom

Member
Joined
Jan 9, 2007
Location
Colorado
TDI
2001 Jetta
Best post, time saver and anxiety saver ever. Thank you.
I used NAPA thermostat $24.00 and housing $8.00. Both came with their own o-ring.
Installation was remarkable and exactly per the post.
Oh, new thermostat locked into the new housing just as described. A BIG frustration saver.
Thank you VERY much again. 2001 diesel 140K miles.
 

PDJetta

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'04 Jetta GLS TDI Pumpe Duce Platinum Grey w/ Leather
Yesterday I installed a VW dealer-bought thermostat (with the VW logo and part number on it). I did not want to take chances in messing up the sealing, so I removed the alternator (took a look at the voltage regular brushes while it was out) and vacuum reservoir first (I left its vacuum line attached). Job went smoothly. I managed to save about 80 percent of the coolant. Only had to add 24 ounces to top it off when done. Drained the radiator and then I decanted another quart or so off of the heater hose flange on the head (pulled the air box and battery for added room). I next removed the coolant bottle and positioned its lower hose into my catch bucket and blew compressed air into the cooalnt bottle's little hose.

I had easy access to the coolant flange bolts with the alternator and vacuum reservour out of the way. The bolts were really tight, but broke loose without issue. I had to pry the old thermostat pretty hard to get it to release. I noticed it seals to the block via a tight metal-to-metal seal. I cleaned the sealing recess in the block well. The O-ring only seals the flange to the block.

The easiest part of the job was just pressing the new coolant flange loaded with new O-ring and thermostat in place and installing the bolts. I got them good and tight. I noticed that the flange had a positive stop, so I did not bother pulling out the torque wrench.

This is an 87 deg. C thermostat. The coolant temperature sensor I replaced about a year ago with a VW one, so it should be reporting correctly. I took the car for a long drive today and ran a VCDS log for coolant temperature. Hottest coolant temp recorded was 90.1 deg C. and that was as the T-stat opened. The coolant temperature evened out at 89.1. Before the T-stat change, the original, 9-year old T-stat gave a maxumum engine coolant temperature of 81.0 deg. C, measured with the VCDS last week.

I examined the old thermostat. It's marked "BTT", which must be the manufacturer identification. It's an 87 degree one too. I placed it in a pan of water and heated it. It appeared to begin to open at 87 or 88 deg. C and was fully open at 90 deg. C, but when I slowly cooled the water, the T-stat did not close completely until about 79 degrees C. There is a black rubber seal in it, but you can not see it until the thermostat opens. Perhaps with age they leak.

BTT is this company:

Behr Thermot-tronik GmbH

http://www.behrthermottronik.de/inde..._id=25&clang=1

Is this the same Behr thermostats you get aftermarket?

--Nate
 
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BARIIINGS

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2011 Audi Q7 TDI Premium Plus - Hers / 2010 Audi A3 Premium Plus - Boughtback
Great write-up! Successful maintenance performed on my buggy! Not a bad process at all. Took longer to get all my tools out due to my disorganization!
 

JBjunior

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Nov 27, 2007
Location
WA/NC
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05 Passat Wagon/05 Passat Sedan/03 Jetta Wagon
Another successful thermostat change. Was reading low on the dummy gauge and VCDS was telling me I had low coolant temperature. Went ahead and purchased a new thermostat and new flange from Bora. Everything went smooth as per the instructions and my flange was still in good condition, but I replaced it anyway.
 

Quiner87

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Jan 24, 2013
Location
Green Bay, WI
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2005 Jetta TDI Wagon
Want to say thanks for the great write up. Allowed a guy like me who can hardly change his own oil to change the thermostat in a BEW type engine. The bottom bolt definitely was tricky, but I got it eventually (note: don't drop that sucker either!). Its nice having a fully function thermostat in there rather than one that never got above 170 F.
 

puntmeister

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Feb 3, 2013
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Arizona
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2004 Jetta BEW
Just a quick couple of comments - I replaced the o-ring on a BEW recently:

1) Removing the bottom bolt on the BEW is indeed a royal pain. Doable with a 10mm socket & 1/4"-drive ratchet, as well as a 5 mm allen wrench...and two fingers.... - but, although I didn't do this - I would suggest removing the alternator. Given the aggrevation of removing with everything in place...

2) The old o-ring was contorted - half in front of the t-stat, half behind - so, clearly the o-ring was the cause of the leak. However, after just changing the o-ring, I still have a leak (worse than before...). The t-stat in the car was after-market - wouldn't latch onto the housing (one housing notch was broken, the other intact).

3) Since I can't really pin down the cause of the leak - aftermarket o-ring incorrect? (seemed a perfect fit...), housing bad? not being able to attach t-stat to housing prior to install muffing everything up? Who knows....so, I ordered all 3, housing, t-stat, and o-ring: new, OEM.

The OEM parts are about double (even triple for the t-stat) what you pay for after-market, but the importance of these parts functioning well, and the sheer aggravation of removing and installing them, its worth the added cost to be 100% it will all work out the first time.
 

TDI_FNG

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Joined
Jan 28, 2013
Location
Kirkland, WA
TDI
2004 Jetta
Increase in MPG?

To all those who were running at 170F and are now at 195F, have you noticed and increase in MPG?

I plan to replace the t-stat when I have the timing belt replaced next, but if I can get a boost in MPG it might be worth the effort now. Otherwise I will just have to live with 42 MPG city/highway. :D
 

puntmeister

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Feb 3, 2013
Location
Arizona
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2004 Jetta BEW
Just a note: as I mentioned above, I ended up replacing the T-stat, O-ring, and housing - all oem. No more leak.

I am fairly certain one of the causes of the leak was the housing - they are plastic, and susceptible to contorting over time. The flange on the housing, right where the O-ring sits, was indeed mildly contorted - definitely enough to let water through.

Take a close look at your housing to see if the pastic ring, where the O-ring squishes against the housing, is perfectly level all the way around.
 

Skol

New member
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Jan 4, 2014
Location
WA
TDI
2000 Jetta TDI
Many Thanks

First off, excellent write-up and images! I was a little hesitant with this being my first VW (2000 Jetta) ever, but it went off without a hitch in under 30 mins.

I was never getting above the lower group of 3 marks on my temp gauge. I went with a dealer part since I was getting the coolant there anyhow. $56 seemed a bit steep but I figured this should be the last time I have to change it.

I'll give the German engineers some credit, (and I was lucky my tabs were still intact on the plastic neck) using an O-ring instead of slobbing on sealant was very nice.

The whole reservoir system seems vastly superior as well, one warm-up/cool off cycle bled the system for me - I just used the reservoir as you suggested.

Seeing how accessible this was and reading this write-up gave me the confidence I needed, thank you again!

P.S. I'm glad you mentioned covering the alternator :D
 

brew1

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Joined
Dec 18, 2004
Location
Richfield WI
TDI
15 GSW SEL TDI
Ditto on the nicely illustrated how-to. I used this as a guide a couple weekends ago.

I swapped out a faulty thermostat with a OEM thermostat and housing purchased from ID parts. Covering the alternator was a great suggestion. I must have been lucky since the tabs on the original thermostat housing were still intact. In any case, I used the new housing since I already had it on hand.

Sure is nice to have the temperature gauge pegged straight up at 190 instead of operating at one to two hashmarks below 190.
 

abused-TDI

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Jul 19, 2011
Location
USA
TDI
2005 VW Jetta
I agree, the directions and pictures are very helpful. I just did my thermostat and thermal sensor yesterday.

I used a 1/4 drive socket with a wobble joint and a 6 inch extension. I was able to get the bolts of the thermostat flange this way. I taped the bolt to the socket when I reinstalled them so it went pretty easy this way.

FYI quite a lot of coolant comes out when you remove the old thermostat even after I drawined the system by removing the lower radiator hose.
 

SFHGolfTDI

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Nov 3, 2003
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Ventura, CA
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2002 Jolf GLS TDI - Reflex Silver (purchased 2011) | Previously: 2001 Golf GL TDI - Indigo Blue (sold 2005)
Hi all, on a 35 mile highway trip, my temp stayed consistently at 78-80C on VCDS. I think it might have gone up to 87 going up a hill, then back down again. Sounds like a new T-stat for me?
 
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tongsli

Top Post Dawg
Joined
Jan 31, 2000
Location
Baltimore, MD
TDI
2000 Jetta TDI, 2004, Jetta Wagon TDI PD
There doesn't appear to be a thermostat change how-to, so I took some pics as I changed mine. This was on my A4 Golf, which is probably identical to the Jetta, and probably pretty similar to a Beetle.

Coolant temperature issues:

If you are experiencing coolant temperature variation, it is likely that the coolant temperature sensor is the problem. They are more prone to going bad than are the thermostats. The needle will be low, and will bobble around a bit. I had this happen once, and replacing the coolant temperature sensor fixed the problem. A couple of years later, my coolant temperature was reading low, just within the next hashmark down from 190 degrees, so I thought my new coolant temperature sensor went bad already. I replaced it again and it didn't fix the problem. I replaced the thermostat, and now the gage pegs right to 190 and hold steady there, so it was indeed a bad thermostat this time. When the temperature sensor went bad, it bobbled and varied more. When the thermostat went bad, it was more consistent, staying in a position that was about one hashmark low.


Anyway, without further ado, on to the How-To:

Supplies:
New thermostat. (Part # 044 121 113)
New O-ring. (Part # 038 121 119 B)
New thermostat flange. (Part # 038 121 121)
50/50 mix of G12 (pink) coolant and distilled water.
Catch pan, rags, beer, etc.

Tools:
10mm socket for engine cover nuts.
T-25 and maybe T-30 torx drivers or bits for belly pan.
6mm socket for lower radiator hose clamp at flange.
5mm hex bit (allen bit) on a 6" ratchet extension for flange bolts.
Torque wrench.



* Remove engine cover.

* Jack up the front of your car, or put it on ramps (set your parking brake!), and remove belly pan. (T-25 torx screws, and maybe a T-30 or two...)

* Remove cap from coolant reservoir, to allow air in as the coolant drains.

* Open drain valve at lower left corner of radiator, on the lower radiator hose. It rotates maybe 30-45 degrees counterclockwise, then you pull the whole knob outward to open it up.


This is all the instructions the Bentley manual gives. I only got about 1/2-gallon of coolant out. I expected to get more than that, but in calling r90sKirk, that's about right. A bunch more drained out when I removed the thermostat, and this was impossible to catch, and also got grunge in it from running down the engine, so have some spare 50/50 mix of G12 (pink) coolant and distilled water handy.

I still have my side skirt attached, and it's in the way. I used a funnel to direct the coolant to a catch pan. A piece of rubber hose would do the trick, too, but I didn't have the right size handy.

* Remove clamp from the lower radiator hose at the thermostat flange. This is just underneath the fuel injection pump:


* Remove the 2 bolts holding the thermostat flange to the block, 5mm allen bit on about a 6-inch ratchet extension.

* Remove thermostat flange. The Bentley says to rotate the flange 90 degrees counterclockwise, but this is impossible given the diamond-shaped opening in the bracket that flange passes through. The only thing to do is to pull it straight back, which will damage the flange. (See picture at the end of this how-to.) You should now have this:


* I covered the alternator with aluminum foil to prevent coolant from spilling out on it.

* Remove O-ring. I used a small, curved pick. Coolant will start to leak out, unless someone has any recommendations for draining more coolant out of the block from some location other than the lower radiator drain. Based on how much coolant I had to add later to re-fill it, it seems I dumped another 1/2-gallon, or slightly more. If you only pull back a small bit of the O-ring, the coolant will run out in a more controlled manner, and not gush out. I was only able to catch about half of it in my oil change pan, because it dribbled everywhere down below.

* Remove thermostat. It should now look like this:


* Clean mating surface on the block.

* Install new O-ring and thermostat onto a new coolant flange. To aid installation, the thermostat holds onto 2 pins that are molded into the flange. Looking down the flange:

*** If you are re-using your old flange and have broken the pins/tabs, all is not lost. Refer to this excellent post by 'cattlerepairman':
http://forums.tdiclub.com/showthread.php?t=148452
Orientation of the thermostat in the block is not important. It doesn't have to be lined up with the tabs, they are just there as an assembly aid.


* Install thermostat/O-ring/flange assembly into the engine block.

* Reinstall bolts and torque to 15 Nm (11 ft.-lb.)

* Reattach lower radiator hose to new flange and tighten clamp.

* Double-check that your radiator drain valve is closed.

* Fill with new 50/50 coolant. I did this just through the expansion tank, and was just patient. Some have said that you can hook up a MityVac and draw the air out to help fill the system. Someone elsewhere showed a method of taking the upper radiator hose connection loose near the battery and pouring coolant into both hoses -- into the block and into the radiator. Fill the expansion tank so that it's at the proper level, and reinstall cap.

* Start car and check for leaks. Watch the expansion tank and add coolant if the coolant level drops.

* If everything seems O.K., reinstall belly pan and engine cover. Pat self on back....you have avoided the dealer once again. :)



Addendum #1:
This is what happens when you pull the old flange off. The original O-ring is pretty well stuck in the block, and holds the thermostat in the block. When you pull the flange, it breaks the 2 thermostat-holder pins.


Addendum #2:
This is a comparison between the OE thermostat ($66 at my local dealer) and an aftermarket thermostat from one of our trusted vendors ($19). The aftermarket thermostat will not attach to the flange. The pointy end is not big enough to catch on the 2 pins. I recommend going with the original VW thermostat. The aftermarket one did come with a new O-ring. The VW one did not, and has to be purchased separately.

The 2 pins of the flange are supposed to engage within the 'arch' on the top of the thermostat. There is no provision for this on the aftermarket thermostat, however. Also, as you can see there are some other differences in construction between the two thermostats.
Did anyone notice or mention that the original sealing ring is square and not round?

I just replaced mine and put a round o-ring back but noticed the original is square like the EGR and Intercooler gaskets/sealing rings

Does it matter? Mine sealed just fine.
 

ScottySK

Veteran Member
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Dec 18, 2012
Location
Beaumont, AB (CA)
TDI
03 Jetta GLS
Square? Or do you mean flattened sides that meet the block/housing?

The seal will flatten once it's compressed, over time/heat cycles, the seal will harden & keep that shape once removed. New EGR seal is "round" as well.
 

tongsli

Top Post Dawg
Joined
Jan 31, 2000
Location
Baltimore, MD
TDI
2000 Jetta TDI, 2004, Jetta Wagon TDI PD
Square? Or do you mean flattened sides that meet the block/housing?

The seal will flatten once it's compressed, over time/heat cycles, the seal will harden & keep that shape once removed. New EGR seal is "round" as well.
http://www.ecstuning.com/Search/3C0145117F/ES343036/



The seal between the EGR and intake manifold is round. My stock lower intercooler pipe to pancake pipe is round.

But as you can see, the 150PD intercooler hose seal is square. As was the seal I removed from my thermostat. I'll see if I can find it when I get home and I'll post a picture
 
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deegingerkid

Beware the Ginger! Vendor
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Mar 9, 2011
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The Left Coast
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"Blurple" 2000 New Beetle 5M 2006 Jetta has been SOLD
Superb write-up. Thank you for doing this.

tongsli,
I'd never use a seal from ECS for my coolant system. OE that you KNOW fits properly or go home. Every one I've ever seen has been round before installation. I know your post is a year old, but maybe you'll see this.
 

respond2us

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Joined
Nov 5, 2004
Location
Tulsa, Oklahoma
TDI
Jetta, 99.5, Custom - Funky Green. 99 NB TDI, 06 Jetta TDI
From the sounds of this thread, it sounds like time to replace my t-stat. My temp guage basically just sits at the bottom. I get a "warm" heat (it's Winter in Oklahoma, low-30's) but the car never blows hot. I had the coolant temp sensor replaced a couple years ago. I have 285k miles on my MKIV (still runs beautifully). Some heat would be nice. Just wanted to confirm on the t-stat. Thanks!
 

shoebear

Veteran Member
Joined
Aug 1, 2002
Location
Colorado Springs, CO
TDI
1998 Jetta, 2003 Jetta Wagon, 2005 New Beetle, 2013 Sportwagen
Just wanted to confirm on the t-stat. Thanks!
As usual, the symptoms could result from more than one malady. But they fit a bad t-stat, and it's pretty easy and cheap to replace it, so I would start there.

VW wants $40-something for a new t-stat, but you can get exact same one for $15 if you buy the OEM (Behr) one: http://www.autohausaz.com/pn/044121113. It even comes with a new o-ring as well.

As a bonus, once you fix the t-stat, you'll probably see your mileage increase by 2-3 mpg, because the engine will be operating in a more efficient temperature band.
 

spanky1

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Joined
Feb 24, 2003
Location
east Tennessee
TDI
Jetta, 2012, platinum grey(6-spd manual)
I'm on my second thermostat change. First one was after 8 years, the next one after 6 years. I've stripped the head on one of the 5mm allen bolts. I'm going to use the Easy Out to get it out, but want to put new ones back in. In fear of losing one of these, I asked the dealer for one of these bolts/screws when I bought the thermostat. They were out, and I didn't think to ask the part#.

Any help with the part#, or the screws specifications?

Thanks
 

chz17

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Joined
May 25, 2013
Location
Boston, Mass.
TDI
2002 jetta TDI GL 5spd, 2004 jetta TDI PD
The thermostat housing bolts part number: N90945002, the bolts are same used on water pump.
 
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