I have been driving with that issue quit sometime. May be in a whole season. It never left me on the road beside the fan kicking on after shutting the car off or the temperature gauge being in 50 dc instead of 90 dc. Only happened twice in a month but mostly begin of the hot temperatures.

Make sure you get it with the O-ring 'cause the one in the old one might get damaged. If you gonna do it yourself don't pull the wire harness rather than the plastic itself. You might damage the wires. Make sure the c-clip is removed before you start pulling the sensor. Off course keep it in a place where it's not going to fall in the engine bay and off course put it back the way you found it. Simple small plastic but without it the whole car will be nothing by leaking water...

Good Luck...

P.S
When it kicked on in my situation starting the car again was my solution to shut it off... Months before that I changed the coolant flange but not the temperature sensor... I wasn't thinking right!

 

Hi I have Audi A5 2010 model, I am experiencing a problem that when on traffic or leave car idle its AC start blowing hot air and temperature start increasing.
I just had an engine piston rings changed and this problem start happening when I was stuck in the traffic for more than 2 hours.
Any help will be appreciated.

 

Coolant leak or fans not working

 

My radiator fan is not working right ac fan kicks on then shuts off and engine fan not working at I have replaced the fcm and replaced my water pump and timing components a month ago when the old plastic pump failed what could be causing the fans to do this

 

Im having this problem too. The A4 B6 2.0 ALT engine seems to be overheating.
The gauge stays at exactly 91°C when it's hot, but it just didn't 'feel' right. Like once it's not, then after more driving, the engine feels even hotter.
When I bought the car, it wouldn't heat up. So I replaced the Coolant Temperature Sensor between the engine & firewall & that didn't do anything.
I also noticed a leak there, so I then replaced the Rear Coolant flange. Its inner lip breaks & that lets the 'O' ring shift & leak only when it's warming up, or cooling down. I expect that will also let air into the system.
The 'telltale' for that is a whitish/,pink powder around the flange. It's a cheap part & not that hard to replace.
No difference.
So I replaced the Thermostat, ( & the Crankcase ventilation hose while I was at it, also cheap, just cut it in 1/2 to remove it ) It was broken where there's 2 plastic resin legs holding the actual thermostat.But, the fans never seemed to come on. Since most of that travel is short trips & in winter, it's not always obvious.
But Summers arrived & it's 15°C+ temps, fans not comming on ( that I know of ) & the top metal coolant hose was really hot, over 100°C on my temp gun reader. Also the top hose was swelled ( pressurised ) hard solid.
If I took the cap off, it would blow coolant out & boil in the engine ( if I did, I did once when it had cooled down a bit )
But if it's supposed the run @ 90°C, why would it get that hot??
i also find out that the Temp display on the dashboard is a 'approximation' & not to be relied on.... It's never shifted over 92°C..

So I replaced the Temperature Sensor ( 2 pin ) at the bottom of the radiator. Hand bled the system.
Now I thought, up untill now, that this Sensor was just a Switch, like on the other A4B5's,. But I'm now sure it's a proper sensor, it's not flat on its base, it has the little cylinder shaped extension like the 4 pin CTS has. That it sends info to the computer.
​​​​​I started it up, drove a bit to let it get hot. Then the fan started up. I also think the engine runs better, or the transmission is different, this could be just in my mind though. It seems to have a tiny bit more pickup from a standstill.n
OK, now I'm sure the lower 2 pin sensor is working ( to check if it was a fan module problem, I turned on the AC & both fans ran, so it wasn't that )
But, once while the engine was hot & the fans not running, I squeezed the upper radiator hose to see if it 'burped' it, and there was a burp & the fans ran, for a bit.

Thinking that there could be a air bubble in the system, I connected a hand held vacuum pump to the Coolant resiviour where the small hose goes in, I blocked that small hose too. It sucked air past the resiviour cap.
So I out a small sheet of ( car tyre ) rubber over the inner ring & screwed the cap down onto it to seal it.
I applied vacuum & got it down to 15 inches vacuum & the top radiator hose had collapsed.
This means there's still air in the system, I expect.
So I took the cap off & ran the engine @ 3000 rpm & it burp3d a lot of coolant & then air out of the resiviour, the level dropped, I topped it up, replaced the cap , bleed the metal pipe & heater hoses and drove it.
It still seemed to get too hot & the upper hose was hard again. Let it cool down a bit.
Took the cap off, it's still under pressure & I lost coolant. Burped hoses & topped it up again.
Ran it till it's hot & burped the hose & the fan started again. It's almost like burping that hose pushed hot coolant past the Sensor, which then told the fan to start up.

after reburping & bleeding the system, running it till it's hot, cooling down again. Then applying the Vacuum, the upper hose collapsed again.
This seems to be telling me that there's a ' Air lock bubble' in the system.
There's been another post about this & the only way to fix it is to use a proper Vacuum Coolant filling system.
This sucks all of the air out of the cooling system, then fills the void with coolant.
Its weird to think that you can suck all the actual air out. But apparently you can.
This way there's no air left in the system, and so when only coolant is added thru the unit, there's no air bubbles.

I can buy the unit for NewZealand $60, = US 40. It needs a air compressor to work & I think it's sucks down to 30 inches of vacuum, twice what the hand held pump did ( I'm buying a proper seal for that too, all its got is a 'O' ring seal on the piston ) the hand held pump never 'burped' any air bubbles out.

So, once I have got the Vacuum Coolant tool, I will try it out & report back.
It seems a good investment & a usefully asset, hopefully it fixes this problem.

 

I got the Vacuum coolant flusher unit but haven't used it as it was a faulty lower Coolant Temperature Sensor & combined with faulty info from the dash temp display unit.
Using a OBD2 I found that the dash temp was 90°C while the actual temp was getting up to 80, it stayed @ 90 on the dash while the real temp gets up to the proper operating temp of 101°C.
So, misleading info on the dashboard in 2 different ways confused the issue of a faulty lower TSU
it takes many driving cycles to be able to bleed the cooling system, I'd use the vacuum filling unit & just do the job once.