Coolant temp sensor leaking

[texadelphia]

I found a bunch of coolant in my belly pan tonight and found that my coolant temp sensor is leaking. Looks like it's coming from around the base of the sensor. The coolant flange and sensor and everything was replaced a year and a half ago. Is this a common thing to fail? My plan is to get a new o-ring for the sensor or would it be better just to get a whole new sensor? I tried to pull it out and clean it tonight but I didn't know it was just going to start dumping coolant so I stuck it back in real fast before I lost too much. Any ideas on how to get it out and back in without losing a bunch of coolant?

[vce1232000]

drain the coolant level below the flange from the [wrench]radiator peacock into a clean bucket for re-use.

[mc_hotmail]

The coolant flange and sensor and everything was replaced a year and a half ago.
I did the same job a year ago. The new sensor came with a wrong size o-ring, so I reused the old one. So far no leak.

Yes, I reuse drained red Audi coolant. Make a paper towel cone-shape filter fitted into a funnel. Good for the environment.

[Jeevan]

Just spend 10$ for genunine oring at stealership. You should be good.
When i did coolant flange and sensor, those aftermarket oring didnt fit right, I had to do the job twice with genuine orings.


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[texadelphia]

I did the same job a year ago. The new sensor came with a wrong size o-ring, so I reused the old one. So far no leak.

Yes, I reuse drained red Audi coolant. Make a paper towel cone-shape filter fitted into a funnel. Good for the environment.

So how much do you drain. Just drain it until it stops coming out? I may just replace what I take out with new stuff because it's low anyway due to the leak so I'll have to buy some fresh stuff.


Just spend 10$ for genunine oring at stealership. You should be good.
When i did coolant flange and sensor, those aftermarket oring didnt fit right, I had to do the job twice with genuine orings.


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Good to hear that it's a common problem for these o-rings not to fit right...although the shop that did the job supposedly replaced the sensor with OEM parts. I guess you never know though.

[texadelphia]

Got this replaced tonight with an o-ring and retainer clip from the dealer. The new o-ring is bigger and a circular cross section and the on that came off had a flat circumference. The new clip was completely flat. The one that came off was curved but it's hard to tell if it got hot and warped or if it was intended to be that way to put spring pressure on the sensor. The other thing is my shop supposedly replaced this sensor when they did my coolant flange 18 months ago. Is it just me or does my sensor look original?

195319195320195321195322195323

[mc_hotmail]

Glad you got it done. The sensor in your photo seems fairly new to me. The one I replaced was original from the factory and it has a lot of green copper rust.


So how much do you drain. Just drain it until it stops coming out?

I've been draining coolant for small jobs a bit differently: use a simple hand pump to suck coolant first out of the reservoir, then from the down tube between the reservoir and the lower part of the engine block. I push the hand pump plastic hose down that tube as deep as I can.

On that note, the Audi ElsaWin manual for all the models I have shows this instruction for draining coolant:

- Unscrew the drain plug -arrow- at coolant hose (bottom left) and drain off coolant.

https://i.ibb.co/x6tvqJC/A19-10111.png

I've never been able to do that in a C5 A6, C5 allroad, A4 B7 and B8. That plug can turn 90 degree and no coolant will come out. It feels like it will break if I turn more than that by force. Has anyone find that plug useful at draining coolant at all?

[texadelphia]

Glad you got it done. The sensor in your photo seems fairly new to me. The one I replaced was original from the factory and it has a lot of green copper rust.



I've been draining coolant for small jobs a bit differently: use a simple hand pump to suck coolant first out of the reservoir, then from the down tube between the reservoir and the lower part of the engine block. I push the hand pump plastic hose down that tube as deep as I can.

On that note, the Audi ElsaWin manual for all the models I have shows this instruction for draining coolant:

- Unscrew the drain plug -arrow- at coolant hose (bottom left) and drain off coolant.

https://i.ibb.co/x6tvqJC/A19-10111.png

I've never been able to do that in a C5 A6, C5 allroad, A4 B7 and B8. That plug can turn 90 degree and no coolant will come out. It feels like it will break if I turn more than that by force. Has anyone find that plug useful at draining coolant at all?

I was able to use that drain to get some coolant out. It turns 90 degrees pretty easily, then it goes another 180 degrees and the knob twists up away from the tube. It is really tight though and I had to get a set of pliers on it to get it to go past the first 90 degrees. That said I only got about 1/2 gallon out and everything that was in the hard coolant line came out on the ground when I pulled the sensor which was probably like a pint or so.

[Jeevan]

Got this replaced tonight with an o-ring and retainer clip from the dealer. The new o-ring is bigger and a circular cross section and the on that came off had a flat circumference. The new clip was completely flat. The one that came off was curved but it's hard to tell if it got hot and warped or if it was intended to be that way to put spring pressure on the sensor. The other thing is my shop supposedly replaced this sensor when they did my coolant flange 18 months ago. Is it just me or does my sensor look original?

195319195320195321195322195323

new oring looks pefectly fine. The shop either replaced with a bad quality oring or didnt replace at all. Those orings go flat only after few years of use with several heat cycles.

the clip is flat and you should be able to install it with bare hands but the removal it needs needle nose pliers

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[Jayz691]

O-rings generally get flat spots over time. Thats the contact point, and heat will cause this. Nothing to worry about, that one ya put in will prob look the same in a few years, with flat spots.

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[Theiceman]

this whole thing is a none issue really .. i was in their last year doing something and bumped the sensor ... sure enough leaked as i had moved it marginally . i keep a stock of those generic orings for this exact reason..

put a 1 litre yogurt container under the sensor, popped it out, caught coolant , replaced o-ring with some syl glide on it, poured coolant back in.

topped up coolant, done.

[mc_hotmail]

then it goes another 180 degrees and the knob twists up away from the tube.
See, you should have written that factory manual. [:)]

[Theiceman]

Glad you got it done. The sensor in your photo seems fairly new to me. The one I replaced was original from the factory and it has a lot of green copper rust.



I've been draining coolant for small jobs a bit differently: use a simple hand pump to suck coolant first out of the reservoir, then from the down tube between the reservoir and the lower part of the engine block. I push the hand pump plastic hose down that tube as deep as I can.

On that note, the Audi ElsaWin manual for all the models I have shows this instruction for draining coolant:

- Unscrew the drain plug -arrow- at coolant hose (bottom left) and drain off coolant.

https://i.ibb.co/x6tvqJC/A19-10111.png

I've never been able to do that in a C5 A6, C5 allroad, A4 B7 and B8. That plug can turn 90 degree and no coolant will come out. It feels like it will break if I turn more than that by force. Has anyone find that plug useful at draining coolant at all?Ive never gotten it to work and i know how to do it... it just gets bonded in their and if you snap it you are buggered.
I just pop the connection off at the rad.

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[ovilla]

I don’t trust any coolant drain valves on any cars. Best to just undo a coolant hose fitting and let it drain out from there. Eliminates any risk of having to buy a new radiator.

[Theiceman]

I don’t trust any coolant drain valves on any cars. Best to just undo a coolant hose fitting and let it drain out from there. Eliminates any risk of having to buy a new radiator.The drain valve is on the coolant hose not the rad.

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[ovilla]

The drain valve is on the coolant hose not the rad.

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Ah yes! You are correct. It’s been so long since I had to drain my coolant.