Coolant leak

[Norretal]

Well, I thought it was all going just a little too well.

I had my car back to the independant after the free Audi health check and had a leaking diff seal renewed, new discs and pads on the rear and a front bearing renewed under warranty and thought the A8 was all sorted for winter....I should have known better

I've been aware of a very small loss of coolant for ages but I've never been able to identify where its going, so have just topped it up when required. I had a good run out on Friday of 120+ miles and when back near home the warning came on the display telling me the level was low. I topped it up an hour or so later when it had cooled and thought nothing of it. However I came outside on Saturday morning and found a wet patch under the car, and making its way down the drive. The expansion bottle had lost about four inches overnight so the leak has obviously developed. I took a look down the front of the engine bay and can see the coolant collecting on the tray, but the drive is sloped so it could be from the middle or rear. I'm taking it to the garage tonight and they'll take the tray off and determine where it's from but I recall a "plastic pipe" being mentioned as a problem with these. Hopefully it's easily identified and repaired, I'll update when it's sorted out, hopefully quickly and cheaply!

On another subject, I fitted the 18" Sport wheels a couple of weeks ago after having the 20" FE's on since April........what a difference it makes to the ride comfort. I can only compare it to putting comfortable slippers on after walking around in brand new leather shoes all day

[Dezzy]

It's likely coming out of the return pipe. There is a metal insert in the plastic pipe and they get hot cold and crack.

[Goran]

I had a similar mysterious slow leak on my previous S8. It turned out to be the plastic pipe between oil cooler and engine. In the end I had the whole oil cooler replaced with a new one - ouch!
My advice, get yourself one of these:
http://www.ebay.com/itm/Aluminum-Aud...29d302&vxp=mtr

I have one ready to go into my new S8 as soon as I notice any sign of coolant loss. Several guys in the States already have this installed from the manufacturer above.
Also get yourself the figure 8 rubber seal for the other connection between oil cooler and engine block. It should be a standard Audi item in a little repair kit with some other seals. No sense in getting a whole new oil cooler if the old one is good.

If you can find a Viton version of the figure-8 seal even better! let us know.

[Norretal]

I said I'd give an update so here goes.............

I left the car with the garage for a couple of days and when I rang for an update I was informed they couldn't find a leak?!? They'd pressure tested it, ran it at "working temperature" while monitoring from all angles, left it cold with paper under it and still nothing. I'd much rather they identified a leak and fixed it but I suppose I'll just have to continue using it until it gets worse. What I really can't understand is how I had a leak while cold yet it lost nothing while running hot, I can't really get my head around that

[Goran]

I can offer a theory, which could be completely false
If plastic pipe is worn, it may expand at different rate than aluminium block and oil cooler housing it connects. When things heat up the rubber seals and plastic expands making a better seal.
My slow leak was just as mysterious, no wet patch in undertray, yet coolant level lower. Someone suggested the coolant evaporates when its a slow leak like this dripping down hot metal surfaces.
For me changing the plastic pipe definitely did the trick. Also look for stains on undertray which look old. they may actually be new just evaporated.
I recently got one of those cheap £12 ebay bore-scope cams, 7mm diameter, they are not bad at all, I already used it to check out something at the back of the engine. Maybe it could reveal the state of that pipe?

[Norretal]

Thanks Goran, that sounds highly likely as the signs are much the same as you describe.

I think I'll buy one of those you posted the link to and have it fitted anyway, it rules it out then and saves waiting for it to fail altogether. I've seen too many mentions of this dreaded plastic pipe to believe it'll be anything else to be honest.

I'll keep you updated on the outcome, thanks again

[Dezzy]

This is where mine was / is leaking, it was very slow but following the red line, i could see it was damp on the small lip.


this is the pipe connected


and this is how it looked with the pipe off

[johnny_quattro]

Thanks for the excellent photos Dezzy, as mine's had an ongoing leak for the last 6 months or so and I've just kept topping her up.

Armed with this new possible source of leakage, I'll have a look at mine later at work under some nice bright lights in our underground car park at work.

Cheers.

John G

[Norretal]

Thanks for the advice and pics Dezzy, another avenue for me to explore