Need help with a coolant leak

[RedTDIowner]

I finally figured out where my coolant leak is coming from after a few years and over 100,000 miles of it leaking. It appears to be some type of plug with a wire coming from it that is directly below where the boost line comes out from the valve cover and goes to the brake master cylinder. I will post a pic below.

 

[RedTDIowner]

Click on this pic and toward the bottom right corner you will see a little green part. Thats the plug that is leaking. You can wiggle it and it starts leaking G13. Its as if there is maybe a rubber O ring in it that has gone bad. Do I need to replace the entire plug or just the O ring? How do you go about replacing it? Anyone know what the part number is and have a video showing how to replace it?

 

[STDOUBT]

Coolant temp sensor. Easy to find online, comes with a little o-ring.
Don't pull it out until you're ready to catch (and replace) a good amount of coolant.
I caught about a gallon coming out of there in a plastic bucket when I did mine.
Make sure you get the old o-ring out, and that you seat the new one nice and flat.
You also want to get a replacement for the little plastic clip that holds the sensor
in place in the metal bracket.
EDIT: P.S. first off, separate the wire harness from the sensor and tuck it away from the coming deluge. plastic baggie and a twist tie works.
P.S.S. Smartest to change it out at each new timing belt since you'll drain the coolant anyway.

 

[Blacktree]

Like mentioned above, that's the coolant temperature sensor. The O-ring on that sensor is a common source of coolant leaks.

The good news is, it's a pretty inexpensive fix. You can buy just the clip and o-ring for $2.49 + shipping at IDParts. They also have the Rein temperature sensor with clip and o-ring for $12.95 + shipping.

Links...

Coolant Temperature Sensor Clip (VW)

...

www.idparts.com

Coolant Temperature Sensor Seal (TDI)

O-Ring Seal for the coolant temperature sensor installed in the plastic coolant flange on the side of the cylidner head. Used on all TDIs. Replace this seal when removing or replacing the sen...

www.idparts.com

Coolant Temperature Sensor Green 4pin w/Seal and Clip (A4)(B5.5)

Coolant Temperature Sensor Green 4 pin. This is the coolant temp sensor for most later TDIs, including PD engined A4 chassis cars. Check your car before ordering, early cars (98-00) use the blue se...

www.idparts.com

 

[WolfgangVW]

Your call but for the price of the sensor you might want to replace the sensor not just the o-ring while your doing it. Another thing you could look at is draining the coolant and replace the tstat while you have the coolant out. Just if you have CTS or T-stat issues in the near future you’ll be draining the coolant all over again. Or your tstat and cts could function perfect for years to come who knows ! Just a pain to have to do the whole process multiple times , ask me how I know lol. Don’t think the thermostat was too much when I did it but can’t remember

 

[RedTDIowner]

Ok, there has to be a catch. It was way too freakin easy. My local VW shop had the clip and O ring in stock for just a couple dollars each. They told me if my temp sensor was working fine to not replace it since my car had over 350,000 miles and was almost 20 years old. No need to take a chance of messing up where the wire and cap snaps on and connects to the sensor. I lucked out and found a rubber plug laying around my garage that fit the hole exactly. I pulled out the sensor and coolant started gushing out but when I stuck in the rubber plug it stopped. I didn't see the O ring so I thought maybe it had dissenigrated. I decided to double check and pulled back out the plug and the O ring was stuck on the end. WooHoo! I then stuck the plug back in so I could put the new O ring on the end of the sensor. I pulled the plug back out and put in the coolant sensor, making sure it was fully seated. Now I expected it to be a pain in the butt to get the clip on but it just snapped in place. I then pulled on the sensor to see if it would come out but it stayed snug. I am going to run some errands in a bit so I will let you know if it fixed the leak. I appreciate all who replied in this thread!

 

[Blacktree]

Ok, there has to be a catch. It was way too freakin easy.

Right? LOL

 

[WolfgangVW]

Keep us posted ! Hope it’s fixed !

 

[Genesis]

It's a VERY common leak source and I've had to change that sucker a couple of times. If I'm doing anything where I have to drain the coolant I change the O-ring because it's dirt cheap and somewhat of a pain if you have to do it later.

 

[RedTDIowner]

It's a VERY common leak source and I've had to change that sucker a couple of times. If I'm doing anything where I have to drain the coolant I change the O-ring because it's dirt cheap and somewhat of a pain if you have to do it later.

Well mine was the original factory O ring. I am surprised it lasted over 350,000 miles, though it has been leaking slowly for over 100,000 miles. I just kept thinking it was leaking out of the big coolant hose coming out the end of the head all this time. Now knowing its problematic I agree that its something that should be replaced each time you do the timing belt. I figure by now someone would have been including it in their timing belt kits. Well I have now driven it close to 100 miles since I replaced it and its still bone dry with no leaks. Thanks for the help fellas!

 

[WolfgangVW]

Perfect! Glad your leak is fixed!!