[Biturbos4] Strange loss of coolant

[John Corbishley]

Mine was a small crack in the reservoir. Only opened up when hot. Almost zero residue

Sent from my iPad

> On Jul 2, 2016, at 01:25, Ti Kan <ti at amb.org> wrote:
> 
> Hi folks,
> 
> Thanks for comments from Al S., Andrew Lundy, Kneale Brownson, Geraldo
> Candela, John Lag see, Mark Rosenkrantz, Chris Semple, Dave Eaton and
> Wylie Bean.
> 
> Here's an update to the problem.
> 
> After driving for a few days (over 100 miles) with apparently no
> more coolant leaks, today I noticed a leak again.  It occurred right
> after shutting off the car from an ordinary 20-minute drive in
> about 85 deg. F weather.  The puddle below the car suggests no more
> than about one quart lost, and that's how much I had to refill to
> get the level up to normal again.  Then, I was able to drive around
> for the rest of the day without any further leaks.
> 
> While looking around under the hood, what I do know is that the leak is
> not coming from the coolant reservoir or the cap.  Everything looked
> dry, there is no G12 residue anywhere that I could see, and the sound
> absorbing liner under the hood was also dry with no sign of hot steam
> on it.  Of course the engine bay in an S4 2.7T biturbo is quite cramped
> and one couldn't see much through the gaps.  I did not remove the
> under-engine cover to look at the bottom side.
> 
> I also know that it's not a problem with the electric radiator fans.
> They operate just fine when I turn on the A/C, and also when the after-run
> auxiliary coolant pump is activated.  Btw, I am running a lower than stock
> temperature switch for the auxiliary coolant pump and fans, so that it
> helps to cool things down after shutting off.
> 
> It's also not likely to be an internal leak (i.e., into the combustion
> chamber).  There is no smoke out the tail pipes, the engine oil
> level looks normal, with good color with no sludge on the dipstick.
> 
> So right now I think I've narrowed it down to two possibilities:
> 
> 1. A pin-hole on a hose somewhere that leaks only when above a certain
>   pressure.
> 2. Electric auxiliary coolant pump
> 
> #1 would obviously explain why I lose coolant only occasionally,
> but would #2 also exhibit a similar symptom?  FYI my auxiliary
> coolant pump was replaced a year and 3 months ago.  That would be
> a really short life if it had gone bad...
> 
> -Ti
> -- 
> 2003 A4 1.8T
> 2001.5 S4 2.7T
> 1984 5000S turbo
> 1980 4000 2.0
> 
>> Hi folks,
>> 
>> My 2001.5 S4 did something weird that I cannot explain, maybe
>> someone out there would have an idea what happened.