Coolant leak at coolant temp sensor... again.

If you are careful insert an extension bar straight through the ports that had the upper two rubber pipes. That may give you a bit more leverage and something to grip hold of. There is a chance the housing is brittle due to age and may break coming off, spray some hot water onto the area at the back where it fits to the block, then wiggle each end of the extension. If still refusing to budge then even more carefully apply a lever onto the ends of the extension bar either alternating on the ends or both together. I think the housing or seal has bonded itself to the block due to oil or diesel. It does look like it is not secured to the block as only the two points hold it on.
 
am I right in thinking that you are removing the entire sensor housing just to replace the sensor? It looks terrifying (bearing in mind how dark and cold it is outside at the moment). It took me 3 attempts to replace the sensor the first time I did it, and it was all down to light - when the area is adequately lit, and you've removed the wee bracket that carries the sensor loom (but which is in the way of where you need to get pliers onto the plastic C-clip), it seems straightforward - once you've done it once. When the light is from the wrong direction / insufficient / shadowed, trying to do it all by feel makes it infinitely more daunting.
 
The reason housing is coming off is to check the o ring between the housing and the block and to check the temp sensor location for extra seal or damage then fit the sensor before refitting the housing. If you look at the picture there is a lot of oil in the area, hopefully not diesel.
 
The hoses looked okay so I don’t think there has been diesel. There is a lot of oil though... and I’m not sure why. It’s not fresh but it is caked on. I cleaned the area if you can’t tell.

So is that stud which is sticking out and circled in red the second bolt? One of the two which was supposed to be holding on the housing? I did remove a nut from it and the housing is spinning in place quite freely so I don’t think it’s welded in place - it seems to be rotating about the area of that stud. Is the stud meant to come out like the other one did? Do I need to double nut it and wind it out?

The exploded diagram from Audi is actually a bit low on detail isn’t it!


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The reason housing is coming off is to check the o ring between the housing and the block and to check the temp sensor location for extra seal or damage then fit the sensor before refitting the housing. If you look at the picture there is a lot of oil in the area, hopefully not diesel.
Ahh - that makes sense ; I thought we were talking about the o-ring on the sensor! Sorry for the confusion.
 
You could do either, try to get the housing over the stud after making sure there isn't a nut still on there or double nut it.
 
Okay. I’m an idiot. It’s off now.

There are TWO metal brackets to remove. One is the wire carrier plate and the second metal bracket is the one in blue. The two round objects in the pic are machine screws which come out with an Allan key to allow the second metal bracket to slide over that stud and reveal... the second nut on the stud which was holding the plastic in place.

the sensor appears to have been in place correctly and the pin holding it properly but it was very mobile. I’ve ordered a replacement from Febi to see if it’s any different.

The gasket between the engine and mount is deformed and stretched. I’m not sure if I did this during the removal ‘wiggling’ phase or if this was the cause of my leak in the first place...

can anyone help me work out how to get a replacement? I have no clue despite some pretty frantic Googling...
 

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Item 18 on the diagram..


037121688

ebay item here


When you fit your new temp sensor align it the same way the pins point now.
Give everything a good clean and include the area this fits on the block you want it spotless. Check there is no damage around the seal area of the housing and check the temp sensor bore.
 
Well that was horrible!

The access felt ridiculous. Even after removing everything I could above and beside the work are the angles are atrocious.

Anyway... I removed and cleaned the housing. The new Febi sensor and clip were fitted and the fit was MUCH tighter. Far less wiggle or play. I also fitted the new gasket for the engine side connection.

I finally managed to get everything back together (a magnetic pick up tool is a must for this job I think) and... it’s dripping steadily from underneath the housing.

I’m hoping that it’s just that the gasket needs to seat and swell a little so fingers crossed it stops.

If not, I’m just going to live with topping the coolant up periodically. I ain’t doing THAT again!

Unfortunately the replacement expansion bottle I also fitted also seems to have a duff ‘low coolant’ sensor!

Not my day!


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Well that was horrible!

The access felt ridiculous. Even after removing everything I could above and beside the work are the angles are atrocious.

Anyway... I removed and cleaned the housing. The new Febi sensor and clip were fitted and the fit was MUCH tighter. Far less wiggle or play. I also fitted the new gasket for the engine side connection.

I finally managed to get everything back together (a magnetic pick up tool is a must for this job I think) and... it’s dripping steadily from underneath the housing.

I’m hoping that it’s just that the gasket needs to seat and swell a little so fingers crossed it stops.

If not, I’m just going to live with topping the coolant up periodically. I ain’t doing THAT again!

Unfortunately the replacement expansion bottle I also fitted also seems to have a duff ‘low coolant’ sensor!

Not my day!


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Awful, isn’t it? The cold weather won’t help, but it’s a pig of a job at any time. I’m crossing my fingers for you in the hope that it’s sorted your issue, unbelievably mine still dripped after all that faff and in the end it was solved by fitting a jubilee clip and throttling the coolant pipe until it stopped!
 
I took your advice @Silverpig and stuck a jubilee on the rear hose that looked like it might be the only other one the drip could be coming from. No luck unfortunately.

I’ve got 5L of coolant so it can just drip until Summer!

Then I’ll think about having another go... maybe... if he’s good.


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Could the housing be cracked?

At £8 for a febi housing with head seal (why no cts seal too) its a no brainer!
 
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I took your advice @Silverpig and stuck a jubilee on the rear hose that looked like it might be the only other one the drip could be coming from. No luck unfortunately.

I’ve got 5L of coolant so it can just drip until Summer!

Then I’ll think about having another go... maybe... if he’s good.


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I feel your pain, having gone through the same experience as you I briefly considered a spot of arson on my car but eventually it stopped when I just kept tightening the clip. I did leave it dripping for a while when I couldn’t get the leak to stop, but it went through so much coolant that I had to give in and strangle it until it stopped.
 
Hopefully you thoroughly cleaned the housing and the block as well as carefully checking the housing for damage especially in the seal area to the block. As above...


When you fit your new temp sensor align it the same way the pins point now.
Give everything a good clean and include the area this fits on the block you want it spotless. Check there is no damage around the seal area of the housing and check the temp sensor bore.

And my earlier quote...

Assuming there is nothing wrong with the housing and no wear in the o ring location, you can reuse the housing


TBH if you are going to take it apart again I would replace the housing, again make sure the head is immaculate where the seal fits and not pitted. Torque all the bolts correctly, you did torque both of them?
 
Hi @audifan

I did my best to clean the engine block where the flange mounts. Frankly, it’s in an impossible location any I couldn’t really get my head into the space to look directly at the head but I did my best with torches and two
Mirrors.

I washed the flange well in hot soapy water (after some degreaser). And I used a medium toothbrush and soapy water to try and clean the engine mounting face itself. Rubbing my finger around the face it felt smooth and I couldn’t feel any nicks or damage (how would they have happened, anyway?).

Access is horrible and I don’t have anything that could torque in that area. I tightened them to where I thought they were before. Then more when it leaked. Then more when it kept leaking. It’s now pretty darn torqued.




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Although in an ideal world it shouldnt be needed maybe a smear of silicone/instant gasket around the seal would solve thid horrid issue (know its a strip down job to try thou sadly)?
 
Could the housing be cracked?

At £8 for a febi housing with head seal (why no cts seal too **) its a no brainer!

** because the seal is supplied with the coolant temp sensor? - I have one ready to go into my project car once it gets warm and light enough again to do this. Useful to know that Febi supply the housing as well though - thank you for that note. Out of interest, do you have the 5-digit part number for this for future reference for all and sundry?
 
** because the seal is supplied with the coolant temp sensor? - I have one ready to go into my project car once it gets warm and light enough again to do this. Useful to know that Febi supply the housing as well though - thank you for that note. Out of interest, do you have the 5-digit part number for this for future reference for all and sundry?
Febi 23720

Cheapest is £7.99 (i may buy one just incase). The comment around the cts seal is simply the fact that i wish they would sell the housing with both seals as it maybe the case you dont intend fitting a new cts but has it needs swapping into new housing. Its a touch daft and may catch folks out which could lead to additional coolant leakage, effecting our wildlife inc cats!
At around a pound for a genuine one i feel its a common mistake in multiple applications by multiple manufactures/part suppliers!!
N90316802
 
I got the car back and had a chance today to try and localise the coolant leak. In the snow. Feels like -6!

I started out by making sure everything was dry (by letting the coolant level go low). Then went about sticking tissue paper all around the area of the coolant flange, above and below.

After topping up the coolant the only bit of tissue paper to start to go pink and damp - was the bit just below the coolant temperature sensor! Again!

I pulled out all the tissue and confirmed it. Yes. Only wet directly under the coolant temp sensor. Nowhere else.

A mirror and torch and the drip is coming off of the push clip foe the coolant sensor!

It must be the sensor gasket that’s leaking now. Despite me just having replaced it. Again. Maybe I need to get a genuine Audi one! How does one actually buy Audi genuine? Crewe?


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