Auxillary radiator leak ????

[alg]

I have had a persistent coolant leak for over 6 months. With normal daily driving it is minimal. But it can be significant if I stress the cooling system (hard and or long drives) enough to drop the level from max to min in a few days.

Car has had new main radiator (end last year) new auxillary rad (2004) new after run coolant pump (last year) most of the coolant pipework renewed during my ownership (last three years).

All clips tight.

At present and all along the only area always to have evidence of dried coolant is the 3 way piping to the aux rad. This pipe was new end last year (previous one had split, you could see it weeping coolant ,wrong side of clip !!) and I thought I had solved it.

It passes pressure testing at dealer but clearly under pressure coolant is getting out. Could the rad have a small hole/split or would this be obvious ? I have spent time with the engine on after a long run trying to see a leak but no luck. The underside of the lower aux rad pipe has been damp but no more than that. I have repositioned that pipe and replaced clip.

Could this be an air lock ???

It seems worse when A/C on. Does that change coolant pump speeds ??

[Rusty]

I located a slight leak on the fan thermostat switch at the bottom of the main rad on my coupe. Quick tighten and it seems to have stopped it using coolant... for the moment! It was not an obvious leak and the fan switch was not loose by any means but there was coolant residue below it but not above. I had my main rad replaced 2 years ago and had only recently had the leak. Worth a check. HTH.

[pastures16]

to add to that
the bottom mount of the main rad cracks which also causes a small leak under pressure

[S-Express]

Hate to suggest it
But, head gasket???
Do a leak down test with the expansion cap off and see if it blows bubbles..............

[alg]

Hate to suggest it
But, head gasket???
Do a leak down test with the expansion cap off and see if it blows bubbles..............

Would I not see coolant contamination of oil on the underside of the filler cap ?? The dried coolant is always in that same place sprayed on the aux rad pipes and A/C compressor

[alg]

to add to that
the bottom mount of the main rad cracks which also causes a small leak under pressure

Main rad and mounts new

[alg]

I located a slight leak on the fan thermostat switch at the bottom of the main rad on my coupe. Quick tighten and it seems to have stopped it using coolant... for the moment! It was not an obvious leak and the fan switch was not loose by any means but there was coolant residue below it but not above. I had my main rad replaced 2 years ago and had only recently had the leak. Worth a check. HTH.

New but thanks for all the ideas

[Dpicariello]

Don't know if this is of any help but since I replced my rad a few weeks back I have had a few drips run down the side of the block and collect on the sump and drip from there. I think this is from the thermostat housing as I was very cautious doing the bolts up (good reason for this but maybe I was a little too cautious). Without stripping everything out I can't be sure but I think this is where the leak is coming from. I don't know if there is any easy way of seeing it without removing lots of stuff but you may be able to get in there with an inspection mirror.
It could be the O ring that has gone (was this and the thermostat replaced with the rad?).

Hope you find the cause.

Dan

[S-Express]

Would I not see coolant contamination of oil on the underside of the filler cap ?? The dried coolant is always in that same place sprayed on the aux rad pipes and A/C compressor

Only if the water channel was leaking into an oil gallery - not if the water channel was leaking directly into a cylinder................

[alg]

Only if the water channel was leaking into an oil gallery - not if the water channel was leaking directly into a cylinder................

Yes but I can see the dried coolant in the area noted so gasket unlikely (but agree a possible leak source if no evidence of dried collant) Plus new short engine block under audi warranty 2003

[alg]

BUMP Ta