[Biturbos4] Strange loss of coolant

[Geraldo Candelas]

When you changed the aux coolant pump did you have them put new hoses? I bet 1 of your hoses that go to it is dripping coolant. 

Sent from my iPhone6+

> On Jul 2, 2016, at 12:25 AM, 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.
>> 
>> A few days ago I drove home as usual, the car ran fine without
>> any signs of trouble.  It was a very hot day so I had my A/C
>> running.  Upon arrival, I parked it outside, and noticed a small
>> trail of water behind the car.  It didn't concern me at the
>> time, thinking that it was just condensation from the A/C.
>> 
>> About 3 hours later I leave to go run an errand.  As soon as
>> I started the car, the auto-check system displayed the big
>> "low coolant" warning symbol.  I shut off the car to check
>> under the hood.  Sure enough, the coolant reservoir was dry.
>> I had checked the level recently, so this is not due to a
>> slow leak.  However, looking around underhood, I cannot see
>> an obvious place where the leak might be.  The first thing
>> that comes to mind was hoses, the expansion tank, or the
>> expansion tank cap.  There was no sign of coolant or wetness
>> anywhere that I could see, except on a small hose that runs
>> from the fuel pressure regulator to the intake manifold.  The
>> hose looks like a vacuum hose to me, it has a woven cloth
>> exterior, but it was wet.  I don't think the hose itself was
>> the culprit, but perhaps the coolant leaked from something
>> and got this hose wet.
>> 
>> I also examined the radiator area, the heater hoses, the
>> plenum area where the heater hoses go to the heater core.
>> I also checked the interior floor carpet... all dry.  There
>> was no musty smell in the cabin.
>> 
>> Hmm.  OK, so I refilled the expansion tank back to the proper
>> level with distilled water and G12 coolant mix.  The total
>> amount I had to pour in was a little over 1/3 gallon water
>> and the same amount of G12, making it 2/3 gallons total.
>> The cooling system capacity was not listed in the owners manual,
>> so I searched for it on the net, and found it to be 1.58 gallon.
>> This means that the system lost 2/3 gallons, but still had about
>> 0.9 gallons in it.
>> 
>> That's enough coolant loss, more than what would only get a
>> small hose wet.  I dried that hsoe with a paper towel just to
>> see if it gets wet again.
>> 
>> I drove the car for 2 days now, and the coolant level
>> is staying pretty much where I filled it.  I don't see any
>> signs of leak, no puddle under the car, no trail of water behind
>> the car.  It seems as if the problem cured itself.  That small
>> hose feels a little damp.  I'm not sure if it's new leak
>> or it's still coolant from before.  The cloth texture of
>> the hose seem to retain some water even after I wiped it.
>> 
>> I am still baffled about this, and carry distilled water and
>> G12 in the trunk just in case, but what could cause an apparent
>> big loss of coolant and then act as if it never happened?
>> 
>> -Ti
> 
> 
> 
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