1.6 fsi coolant loss resolved

Hi all. I have had an issue with a small amount of coolant being lost graduallly over periods of time. I would fill up the expansion bottle and check it again a month later and find that it was back on the minimum. I couldn't see any visible leaks so just kept topping up. Then the other day I visited my parents and they called to say had I got a leak? I had a look around the car and found a small amount of coolant dripping from the undertray. I had a look and feel around the car and couldn't really see anything until I accidentally touched the coolant temperature sensor, which is mounted in the thermostat housing. Everytime I touched it my hand got coated in coolant and it was very loose. Its only held in by a spring clip but is in a very difficult place to get to. I went down to my local dealers and purchased a new sensor and sealing 0-ring gasket. And a couple of bottles of G12 coolant.
I waited for the car to cool down and then managed to get the spring clip out to find the 0-ring gasket was completely shot. Perished and very little left. Installed the new gasket and sensor (which I didn't really need) and then fiddled around until I got the spring clip back in place.
Now all sorted and coolant seems stable.

Cost me about £40 with the sensor but could have just been £1.06 for the 0-ring and some G12 if I wanted to try and return the sensor.

Well pleased as I was fearing the worst as I had read about thermostat housings leaking, which given the location looks very fiddly to change.

Hope this helps anyone else with a similar undetectable leak.

Well done . I have done a few of these, it's a fiddly job, and it seems fairly common on the 1.6FSi.


Cheers
Sarge

Any chance of pictures of the area. I think mine needs doing too!

FOR 1.6FSi ENGINE

Part 11 is your temp sensor
Part 13 is the retaining clip
Part 17 is the seal that perishes




Cheers
Sarge

Sorry but I havn't got any pics. But the exploded diagram from Sarge shows where it goes. The sensor is just behind the ribbed pipe on the right side of the engine that goes from the engine block to the manifold. No room as usual but it can be done without removing anything. It took me about 20 mins to do and I had to put a whole container of G12 fluid in as quite alot escaped.

very useful post.

I think mine needs doing.
I changed a couple of hoses as they were leaking too, but Im still loosing coolant somewhere ( very slowely )

stupot555
whole container of g12 - how big container ? 1l ?

Yes. I put a very small amount of a second one in aswell.

brill. thanks for the info.

Just checked the g12 bottle and its 1.5 litres.

OK, I think I did it and I take my hat off to gynecologists everywhere. Plumbing and probes in such tight spaces are not a good combination unless you are very dexterous!

OK just a few points, and one question.

It took me an AGE to find the sensor, basically you can't see it. You have to do the whole job by touch.
To find the sensor, stupot is correct. However it took me an age to realise which ribbed pipe he was on about.

So here goes with my description to clarify (or add to the confusion).

OK you need part number P AN 903 168 02 Described as O-ring B0905C cost £1.06 plus vat.

First locate the sensor. This is at the passenger side of the engine (right side as you are working).
If you look at the side of the engine you will see a metallic ribbed pipe approx 2cm in diameter.
To the right of this and slighty lower down you will see one of the fat coolant hoses.
You have to reach down with your right hand down the RH side of this fat pipe and reach far over to the left and sort of up!
Have a fumble and you will feel the temp sensor, wire and securing clip.
To remove the clip I slid a 2.5mm allen key into the gap between the clip and the housing and used this to pry the clip free.
I then dropped the clip! It is thankfully magnetic!

The sensor came out easily allong with about 1.5litres of coolant.

The old rubber ring stayed in the housing and had to be poked out by my little finger....very tricky to reach.

The old ring was really in bad shape, soft and crumbling. It also had a flat face to it, instead of being round profile like normal 0-rings (By this I mean round cross-section, not round as in the overall shape of the o-ring).

NEXT the reassembly...

I fitted the new o-ring onto the sensor (its slips off easily, so be careful not to lose it at this next step!).
Then push the sensor back into the housing as far as it will go.
Replace the clip and you are good to go with topping up the coolant.
1.5lite of coolant was £8.25 plus vat.

Now the question....my sensor still felt wobbly once fitted. Is this correct? With the clip in place it won't come out (so it is held in place) but I would have expected a tight fit with the o-ring under greater compression. ??????

Big test drive is tomorrow (did oil, sparkplugs today too! pre spring 77,000 mile fettling!).

Hi
I have 1.6 fsi and my coolant needs topping up every couple of days and and there is water under the car, garage looked but couldnt see anything ! Also engine management light is on and the faults said combustion failure . any ideas as they tried the coil packs but they were ok, any ideas, I have only had it a week.

You need to get a scan on the car.

chb glad you got yours sorted. Sorry, I know my explanation was a bit brief. Mine also has movement but has no coolant loss. I have done a few miles now and had no drop on the expansion tank so very pleased.

Here are pics to help!
In the first picture the ribbed pipe is centre frame.
In the second picture you can still see the ribbed pipe (between the blue bolts)
You can also see two braided hoses, and out of focus the fat coolant pipe that I refered to.
You put your hand between the braided hoses and round the back of the fat pipe.

I havent even tried to do it it seems so tight..
I have seen this sensor though and think its green as I recall. I didnt try because I could not see a drop of coolant around that sensor, and when I pushed my fingers there it was all dry...

If its dry around this sensor does it mean its not the problem ?

Hard to say if it should be wet or dry.
My coolant loss was VERY gradual...ie 100-200ml over a couple of months.
Given the proximity to the engine and the temperature in this area, I would not expect the part to be wet.

My temp sender had never been removed since 2003 when the car was built. The rubber O-ring was absolutely shot. It was crumbling and soft.

So in summary I think this certainly needed replacing. It will take another couple of months before I know for certain whether this was the only culprit!

I have some news
Took my car to mechanic asking to replace oring on temp sensor due to leak. He said with confidence that its not a seal under sensor but most definately gasket on the housing. There are to gaskets there. One on each end. He has taken housing out and indeed these gaskets were shot. Replaced but when trying to fit this back in a flange on one of long pipes going out of housing has cracked ( worn plastic ) Im now on my way to get it ( 50 quid incl seals )
So its not just a simple oring in my case

Pipe were flange has cracked its 032 121 065D 45 quid + u need two seals for it
Gaskets for housing thats 6 pounds
Oring about 2 pounds
60 labour

Also we managed to snap off some kind of sensor that sits on pipe union element. Pipe union is 032 121 121 N
Sensor isnt sold separately and can only be replaced with the whole pipe element ( 70 quid )
Sensor was put back in hoping its still gonna work
Damn audi

Same problem, please help: no engine light at the moment. One month ago I had the coolant light on, I filled with about 150ml, all ok. After 3 weeks (last week), after a 10 miles trip, oil light on and after a few seconds the coolant light too. Luckily I was parking in front of the house when the car started to smoke from the exhaust and from the water tank. Apologies for my English, I'm doing my best. I've waited for the coolant to cool down and filled with coolant, expansion tank was empty. I also filled with oil, my bad, without checking the oil level (I've filled a bit too much). Just to mention than in the expansion tank I have broken pieces, ordered a new one. For 2 day all was fine, than one morning after one mile, the car started to drawn/missiles, lots of white-blue smoke from the exhaust and a bit smoke from the engine. Managed to park and called RAC, they advised I have filled too much oil but no explanation for the boiling coolant in the expansion tank. No warning light at all this time. Left the car in the service 2 days earlier as I was booked anyway for full service and timing belt kit with water pomp replacement anyway. This was last Thursday. Today I've got the car back, full service saying nothing's wrong with my car. 20 seconds after I left the service, it started drowning again and I had smoke from the exhaust again, nothing from the expansion tank, no warning light. Pulled over, called the service (they were closing), I'll go back tomorrow. Heading home after the call, no more smoke, but after a few second in trafic the temperature went from 60 to 95", when I got home I have checked the expansion tank again and it was hot. From the service to my home is 1 mile. I have leaks around the expansion tank and outside the car on the grill in the opposite side of the expansion tank. I am a foreign women with poor English in UK and anywhere I would go I'll be treated as I know nothing, can someone please help me find out what's wrong with my car? Thermostat, radiator stuffed, broken fan, what could be?

Hi,

Sorry for the problems with the car. Several possible causes spring to mind but without further information difficult to say but from your description I am guessing head gasket problem. It's too late at night for questions and I can only suggest you drive the car a short distance to your local garage (check oil and coolant before starting), describe the symptoms including oil overfill and see what they come up with after investigation. You seem quite articulate, albeit a few bits of your post are not clear but stand your ground and if you are not happy take the car to another garage.

Regret to say it sounds expensive.

Andy

Thank you Andrew, will check oil and coolant tomorrow morning. I had a feeling it might be the head gasket, that's only around £30, the fitting is expensive. I have previously done a general check in Halfords and guess what, according to them I have to change all the gear box, clutch and fly wheel... nothing else. So this time, after recommendation, I went to Formula1...I'll see tomorrow.
I wish I would be a mechanic!