temperature sensor install question

jbuddy

Well-known member
Joined
Sep 12, 2008
Location
Hampton NB
TDI
03 Jetta TDI
Weird thing happened, coolant temperature sensor became dislodged and
coolant drained. Having a hard time getting sensor in place to put clip on
to secure it. Greased, cleaned opening, pushing hard can't seem to get in
in far enough. Any tips? Changed it a few months ago and bang it just pops
out I guess, the clip was still on. I guess I did not have it installed correctly
when I changed it several months ago. Videos show just pushing it in.
I need some tips or tricks to install it properly please. Should say 2003 jetta
tdi alh.
 

phaser

Veteran Member
Joined
Apr 18, 2004
Location
Oregon
TDI
2004 Jetta PD - 490k
Where is the old o-ring, did it come out when you removed the sensor?

These o-rings rot with time and can get stuck in there and come out in pieces (been there and done that).

In any event, make sure the old o-ring has been completely removed, and replaced with a new one.

It only fits one way, and should go in easily.

.
 
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jbuddy

Well-known member
Joined
Sep 12, 2008
Location
Hampton NB
TDI
03 Jetta TDI
old o ring is on the sensor, will replace with new o ring. Can't imagine I didn't have the
clip on properly and it stayed in place for several months almost a year. Just find it so
hard to push in enough to easily put the clip on.
 

phaser

Veteran Member
Joined
Apr 18, 2004
Location
Oregon
TDI
2004 Jetta PD - 490k
Just find it so hard to push in enough to easily put the clip on.
The sensor should go in easily, and there is a bit of a hard push right at the last so the o-ring seals, and then the clip should go on without difficulty.

And I would stick my finger in the hole just to make sure it's clean.

.
 

jbuddy

Well-known member
Joined
Sep 12, 2008
Location
Hampton NB
TDI
03 Jetta TDI
I will put my finger in and try to make sure it is clean and then give it another try.
thanks
 

Genesis

Top Post Dawg
Joined
Feb 26, 2003
Location
Sevier County TN
TDI
'03 Jetta Wagon
Yeah, stick your finger in there and make sure there isn't a second O-ring (or pieces of one) in the way. Push comes to shove get out the inspection mirror and flashlight.

It should go in (with the O-ring) without much drama at all.
 

where2

Veteran Member
Joined
Oct 29, 1999
Location
North Palm Beach, FL, USA
TDI
One '13 JSW_TDI & One '04 Variant_TDI
When I swapped mine, I was glad I ordered a new plastic clip. The old clip was warped from the pressure of the old O-ring which had been abused by my leaking tandem pump (some passing diesel caused the old O-ring to swell). There is NO way I would have been able to re-use the old O-ring, or fit two in there where the swelled one was.

For making the new O-ring slip into place, use silicone grease, or other rubber safe lubricating fluids you happen to have around the house.
 

jbuddy

Well-known member
Joined
Sep 12, 2008
Location
Hampton NB
TDI
03 Jetta TDI
Well I got out the mirror and flashlight as suggested and was able to see quite a bit of
build up in the hole so I cleaned it out with pick and shovel, waiting on a new o ring and
clip but just to see used previous o ring and was able to push in much easier and get old
clip on but old clip doesn't seem very snug. Will use new o ring and new clip when arrive
tomorrow hopefully....
 

jbuddy

Well-known member
Joined
Sep 12, 2008
Location
Hampton NB
TDI
03 Jetta TDI
Success thanks for the tips, just a build up of crud inside. Replaced with new o ring
and clip. Sensor went in nicely. Love this site.
 

CopaMundial

Veteran Member
Joined
Jan 30, 2011
Location
Southeastern PA
TDI
03 Jetta Wagon 5sp (New to me Oct 2014) 03 Jetta 5sp (RIP Aug 2014)
Success thanks for the tips, just a build up of crud inside. Replaced with new o ring
and clip. Sensor went in nicely. Love this site.


Was the wrong coolant used at some point in the cars lifetime?
 

Genesis

Top Post Dawg
Joined
Feb 26, 2003
Location
Sevier County TN
TDI
'03 Jetta Wagon
Yep -- I had an O-ring on my temp sensor basically disintegrate on me a couple of years back; I've owned the car since it came off the boat and it has never had anything but the proper VW coolant in it.
 

gfnetadmin

Veteran Member
Joined
Jan 30, 2008
Location
Ledgedale, PA
TDI
97 Passat
Any suggestions on disconnecting the coolant sensor connector? Not much room to get a fat finger on the tab at top of the connector, I've read the connector is the same type as the MAF? Does the tab squeeze in or does it get pushed outward towards the wires?
 
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UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
It was mentioned that the O-ring came out, but not whether it came out the FIRST time the CTS was removed (original bad one was replaced). Sounds like that O-ring never did come out completely (hence revisiting this issue).

gfnetadmin, I'd remove the airbox (if a manual trans) for more room, pull the old CTS out WITH the harness attached, make sure old O-ring came out, and then pop the new CTS in (with O-ring lubed [w/coolant]). At that point you can mess around with the harness connector as long as you want w/o worry of losing coolant:D If the old CTS comes out without the O-ring then slap it back in and consider having a pick and such available for the next shot.

One tip that I had read, and use, is to loosen up the cap on the coolant overflow bottle, squeeze the upper radiator hose as much as I can (flatten it out) and, while holding the hose still collapsed, screw the cap back down. Theory is is that this will create a bit of vacuum in the cooling system, which helps reduce coolant loss when you're replacing the CTS (put a rag down there to catch what does come out- I recall losing only a very small amount).
 

gfnetadmin

Veteran Member
Joined
Jan 30, 2008
Location
Ledgedale, PA
TDI
97 Passat
Thanks for the advice, car is an automatic. I hadn't planned on pulling the CTS, actually trying to diagnose glow plug problems, thought I'd pull the sensor to give me more time to measure voltage at each of the GP plugs on the harness. I'm assuming disconnecting this sensor does the same thing as my B4.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
To disconnect the harness you have to push the tab in toward the wire and kind of push the whole thing toward the CTS a bit and then pull back. I've only ever done one of these things and I "think" it's the same clip style as on the MAF- if that's the case then just practice on the MAF. With the automatic you've got a lot more room (don't have the coolant heater stuff in the way) to access the CTS.
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
Well I got out the mirror and flashlight as suggested and was able to see quite a bit of
build up in the hole so I cleaned it out with pick and shovel, waiting on a new o ring and
clip but just to see used previous o ring and was able to push in much easier and get old
clip on but old clip doesn't seem very snug. Will use new o ring and new clip when arrive
tomorrow hopefully....
I had the same with mine when I changed it a few months ago.
Took me quite a bit of time to get what was left out.
The old sensor was destroyed before coming out with 1/4 of the o-ring attached.
Funny, I've been reading about this more often. :confused:
 

Fahrvegnugen

Veteran Member
Joined
Jan 21, 2017
Location
Burlington Vt
TDI
01 golf 1.9 alh gls silver
Today I replaced my black coolant temp sensor with a green. No crud in hole, old plug was firmly stuck in housing, easy to feel it in there, but 3 broken clips, one blistered thumb nail for the connector clip and lots of coolant later, the fourth one clicked on and it isn’t leaking coolant. It was difficult to determine how far in to insert the sensor. Only after removing the air filter box was I able to align the clip whilst simultaneously moving the sensor to get the clip to click. The upward pressure on clip needed is quite gentle.
I swapped out scorched autolite glow plugs, (one scarily overtorqued one) with some Beru ones, thanks metalman!! No more cel for the first time since I’ve owned the car! Temperature drops on highway but needle generally stays at 190° now.
I notice some debris in coolant reservoir that looks like dirt, and now I have to get all the coolant off the trans housing.
 

Franko6

Vendor , w/Business number
Joined
May 7, 2005
Location
Sw Missouri
TDI
Jetta, 99, Silver`
I get the issue with the temp sensor.

First, the sensor does turn in the housing. Turn it so that the wiring connector is most convenient to detach. We have this crazy green skinny screwdriver that is about 6" long. I bent the last 1 1/4" about 75-80 degrees. The tip of the screwdriver flat is just about the width of the tab that releases the wiring connection. PUSH the connection together, insert the bent screwdriver into the release and voila! It usually releases very easily.

Other trick, put a little bit of axle grease onto the seal, install o-ring on the temp sensor and push into the hole. The plastic hairpin is also something you can install more readily if you turn the sensor for your convenience.
 

Fahrvegnugen

Veteran Member
Joined
Jan 21, 2017
Location
Burlington Vt
TDI
01 golf 1.9 alh gls silver
I got a little screwdriver for free from a Fueling station counter that fits in the connector, which I reluctantly use for this. I’m always worried tab will break. I’ll try to make one of these screwdriver tab release tools. Thanks!
I used white lithium grease on the o ring. I pushed it into housing with connector attached to sensor, I think it would be easier to get plastic hairpin to click on with connector unattached.
 

Genesis

Top Post Dawg
Joined
Feb 26, 2003
Location
Sevier County TN
TDI
'03 Jetta Wagon
I broke the tab on the plug long ago on my '03 (the plastic gets quite brittle over the years) and now use a pair of zip-ties (the small size, ganged together) to secure the plug. It works...

These sensors seem to either start leaking (the O-ring dies) or read wonky somewhere around 5 years of age in my experience. They're not expensive or hard to change, and if the O-ring is leaking you may as well change the sensor too, because it's probably not far behind in terms of dying, and I've never been able to do it without making a decent mess under the car. I always take the pan (or panzer plate) off first otherwise you wind up doing that anyway to clean up, so.... yeah.

It's the only sensor that my '03 has consistently needed changed on some sort of interval. I did have a MAF failure maybe five years ago, but other than the CTS all the other sensors in my car are OE. IMHO you could make an argument for changing this thing (along with the thermostat and housing) when you do the timing belt, since you already have to drain the coolant to change the water pump and thus you'd avoid both the mess and hassle.
 
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wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
These sensors seem to either start leaking (the O-ring dies) or read wonky somewhere around 5 years of age in my experience.
You may be right, I changed mine twice around that time frame.
Plus getting around to it time. :D
 

imbrian

Active member
Joined
Aug 31, 2019
Location
vt
TDI
03 jetta wagon
I thought I’d give my experience with CTS replacement for posterity.
I run an 03 wagon, has 257k on it. CTS has been faulty for a long time, been having weird idle issues lately so I decided to do the job, knowing that it would be serious hassle irregardless of how ‘easy’ it is on paper.

I figured hassles would come because of how dirty and corroded my engine compartment is. The whole life of the car has been on salty VT roads. Got a Delphi replacement from rock auto. The plastic clip broke rights away taking it out, the connector was surprisingly easygoing, but the sensor wouldn’t budge. I could rotate it but no budge.....and this is with airbox removed, plenty of room. I got impatient and tried a bit of prying with a screwdriver through the slot the clip goes into......then it happened; broke off a nice chunk of the housing.

Luckily I got a guy I can get parts from. After I got the housing off it took a handful of serious blows against the workshop countertop to dislodge the sensor!! No way that would’ve came out with the limited leverage you have in there.

My two cent opinion is .....if you need to replace yours and you think you might have the slightest difficulty you may want to get hold of the housing before you dive in. There’s bunch of threads here with great information about changing these out, but check the dates.....yer not changing the CTS on a car with 120k, those threads are old and these cars are getting older, corrosion welds those buggers in.

Thank you to all the people here, this place is treasure.
 
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