Coolant leak at coolant temp sensor... again.

Pinkythelabrat

A2OC Donor
My TDi75 is leaking coolant again and it seems to be from the back of the block where the coolant temperature sensor fits... again.

This happened last year and I replaced the sensor and fiddly clip and that seemed to sort it. For a while.

I’m assuming that’s the problem. Bad seal. Happy to hear alternative suggestions though.

The clip was plastic and really fiddly. Does anyone have a recommendation for a decent green sensor that comes with a metal clip?

Thanks


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From the diagram below. I would disconnect the 3 water hoses and electrical connector from the sender then unbolt item 17 from the block.
Now with it in your hand carefully check the o ring on the back where it mounts onto the block. These seals can leak. You can also now check the housing for cracks or damage. Remove the temp sensor and look for signs of the coolant leaking past either around the outside or inside of the sensor location o ring. Assuming there is nothing wrong with the housing and no wear in the o ring location, you can reuse the housing but replace the o ring before refitting to the block. Before you refit to the block its very easy now to replace the temp sensor with either a new one from Audi or if happy with the seal and sensor the originals ( I would replace them). Make sure the sensor plug points the same way as the one you removed. Refit, refill, burp and go.

You could also refit the parts to the car, fill and bleed with the correct coolant then take for a drive.;)



1609165338336.png


If you have had a tandem pump changed there is a chance the leaked diesel has eaten into the plastic enough to cause it to leak especially where it bolts to the block.
 
The clip was plastic and really fiddly. Does anyone have a recommendation for a decent green sensor that comes with a metal clip?

Thanks
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I can vouch for the fiddliness having tried to remove by hand and the other trick with a piece of tied-on fishing line - I eventually realised that I had a pair of no-name DIY shop 90 degree medium-fine pliers in my old rowing toolkit that work a treat for installing / removing these sensor clips with ease without need to have double-jointed wrists - it is now the first tool I look for when I think about doing this job (I have another one to do on my project car once it warms up again outside).
 
Are you positive the clip is in correctly? Twice i thought i had mine in only to find it felt right but wasnt!

What sensor and seal have you fitted?

I like beru
 
Good afternoon,
I had a moment free between showers and got the lamp in to have a look and a feel around.

The leak is definitely from the sensor. It’s a steady drip even with the engine off. The sensor itself feels VERY mobile but, as far as my fingers can tell, the clip is pushed in properly. The slightest pressure and the sensor wobbles over at least 15degrees in any direction - that doesn’t feel right.

I didn’t get enough time to scope out how ‘item 17’ unbolts but thanks for the tip. I had no idea that bit could come off! It started sleeting before I could figure out bolts etc so I’ll have another look when I can. Access looks rubbish though!

I wish my car would only break things in Summer when it’s warm and dry and light outside. My MOT is in a month too so best get this sorted...

Cheers chaps

Alex.


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I had a nervous shudder when I started reading this thread, I had exactly the same problem with mine last spring which pretty much pushed me over the edge. I removed the plastic junction piece in the end to ensure a proper fit/seal of the sensor, and frankly it’s a pig of a job to do. It’s not quite as bad as the thermostat housing but it just makes you wonder why Audi made it so difficult to do!!

I also had a leak from the pipe above the sensor which fooled me into thinking that the sensor seal was leaking again, provoking more swearing, wailing and gnashing of teeth, so I ended up replacing the securing clip with a jubilee clip and tightening it to within an inch of its life.

My car is suffering from the slow warm up in this cold weather which may be down to the temperature sensor, but I was so put off by the faff I went through changing the last one that I won’t risk doing it again! Horrible job!
 
Hi, are you sure the O ring is in place? I think thats item 5 on the picture? On my 1.4 petrol that I did a lot of coolant work on recently I once fitted the sensor and the O ring was missing (long story) and it wobbled around no end, wiht the O ring it still rotates surprisingly easily but doesent wobble.
 
Sorry another idea is, if your new sensor came with the O ring i place, did the old O ring stay in the housing so that there 2 and no its ot locating properly? Anway none or 2 haave a look!
 
Good afternoon,
I had a moment free between showers and got the lamp in to have a look and a feel around.

The leak is definitely from the sensor. It’s a steady drip even with the engine off. The sensor itself feels VERY mobile but, as far as my fingers can tell, the clip is pushed in properly. The slightest pressure and the sensor wobbles over at least 15degrees in any direction - that doesn’t feel right.

I didn’t get enough time to scope out how ‘item 17’ unbolts but thanks for the tip. I had no idea that bit could come off! It started sleeting before I could figure out bolts etc so I’ll have another look when I can. Access looks rubbish though!

I wish my car would only break things in Summer when it’s warm and dry and light outside. My MOT is in a month too so best get this sorted...

Cheers chaps

Alex.


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Alex. Was it an oem sensor or aftermarket ?
I’m thinking if aftermarket the O ring may not be the correct size. The original is very chunky and I’ve never seen anything like in in the boxes of multipurpose O rings you can buy
If it’s a thinner O ring that you fitted the. That would account for the leak and the excessive movement. It certainly should not be able to wobble around but it’s not what you would call a tight fit either

It’s a common fitting across the vag range so should be obtainable from a good motor factor

I would keep away from greases etc unless you have rubber friendly ones

Cheers. Paul


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It was aftermarket. I think febi maybe... it looked okay. Wasn’t the cheapest on offer.

I was hoping someone would say that removing the whole assembly is super easy! oh well. That’s a shame. The thermostat almost killed me!

I replaced the sensor last time in the snow and dark so maybe I did miss an extra o ring... getting tempted to just fob it off on the garage to sort along with the MOT.


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Removing the housing is not super easy, but not that difficult. Disconnect the water hoses first. The 2 bolts that hold it on have a bracket fitted over the top, remove that then take the bolts out and disconnect the temp sensor plug. You will loose a lot of coolant but the housing will be completely off the car. You can then check the condition of the housing and remove the temp sensor, noting which way round the plug sits. Once the temp sensor is out you can make sure there was only one rubber o ring in there and not two of them. You will also be able to fit the retaining plastic clip and see once it is in how much play there is between the sensor and housing. Assuming that the housing is completely undamaged and has no splits refit it with a new o ring. Rebuild is the reverse of removal, just remember to plug the temp sensor in and fill and burp the coolant system with the correct coolant.
 
Using @Vic picture, you can see one end of the bracket that is on the housing bolts, the other is forward/ lower just out of picture.

1610474799581.png

So once the bracket is off remove the 2 bolts that secure the housing to the block.
 
The second bolt (very dirty) can be seen in this picture. It also shows the other 2 hoses that need to be disconnected in addition to the one in the above picture directly above the temp sensor...


1610475059171.png
 
With 2 seals i would be very suprised if you can get the retaining clip in but cant say i have ever tried.
I fitted a Beru sensor (murrys direct ebay) and on a seperate sale but a genuine seal (could crew audi supply if you have any problems?)
 
I really shouldn’t even try...

I got three of the hoses and one bolt off of part 17 - the coolant sensor housing - but I can’t get it free!

it seems to be rotating around the section marked in red. I undid a nut from that stud but it’s not coming free. The little box section marked in blue seems to be holding it in place and the two other circular thinga DONT seem to be nuts.

It got dark and I was freezing and about to go and get a crowbar on it so I thought best to give in and ask for help. Again!

help!
 

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