I didnt think too much of this at first. It has happened maybe 4 times in the last year. The first 2 times I chalked it up to the iffy blue reservoir cap. The first time, I bought a new one. The second time it happened, I finally put that new cap on

Basically what happens is when I had shut the car down, the expansion tank seemed to bubble over around the cap, with water/coolant running down onto the exhaust and ground. It seems to bubble out a good ammount of fluid, needing to be refilled. It made sense that the first time, I needed to change the blue cap.
Driving conditions were as follows, the first time, it was at the end of a track day. pulled off of my last lap, and there it bubbled over. No other leaks noted. Each of the other 3 or so times, it was just ordinary normal extended driving, 30-45 minutes around town with varying outside temps of between 70 and 90*. One of the times, it bubbled over AS I was waiting at a stoplight. When this happens, my coolant refill light will come on, and temps will climb slightly with line going to the edge of the ZERO in 180. Never any hotter than that. No milky anything in coolant tank. no radiator or other coolant leaks noted.

So possibilities i have are:
Head Gasket on its way out (overpressurizing system on shutdown)
Another faulty expansion cap (crap caps)
cracked expansion bottle neck (bubbling around cap)
too much water in the coolant lines (boils easier @ lower temps)

any other thoughts? blockage in coolant system? radiator issue?

 

Have you otherwise noted any coolant loss that has not leaked visibly on the ground? - This could point to a headgasket problem.

But if not, I would inspect your expansion reservoir closely.

Chris.

 

only time i had similar experiences with inexplicable leaks from the cap were after bleeding the sytstem i had inadvertently left the breather portion "unsnapped"? so it "breathed"... a lot until i discovered my negligence. i doubt you have the same measure of absentmindedness as i did. but it was a thought. but i've had bad caps and old cracked exp tanks too.

 

no other leaks or loss of coolant noted at all.

ive double checked that a couple times, always closed!

 

figured ya had. i'm just amazed at the stuff i forget to completely tighten, like the oil tank drain plug .. once. that was comical
i finished my radiator troubles last week and after bleeding/topping the system it was leaking from that breather pretty seriously..freaked me out for a minute. good luck with yours.

 

A couple thoughts; the experts will weigh in as well I'm sure.

If it were a head gasket, generally speaking, you would be seeing a fairly constant loss of coolant, rather than the occasional you mention. Also you would get a faint scent of burnt coolant out the exhaust. When was the last time you changed the oil? A head gasket leak also often allows coolant to be drawn into the oil galleries and vice versa (read that as BAD) which turns the oil into a substance resembling brown mayonnaise, or droplets of oil visible in the coolant tank. Since we don't have a dipstick to check for coolant on, you can check for coolant condensation under the oil fill cap, or drain the oil and look for any milkiness. All that being said, a head gasket failure is extraordinarily rare on these engines AFAIK.

It's more likely your water to anti-freeze ratio is well below the recommended 50% min-60%max ratios. As coolant loss is noted, some folks (not accusing here) tend to just add water to make up the loss. This brings the ratio of anti-freeze down quickly. Hot spots around the turbos, exhaust manifolds and cats can cause localized boiling on shut down when it heat soaks and there's no longer circulation via the water pump. Easy enough to check, siphon a sample out of the res tank and have the local auto parts store test it. Worst case, change it with fresh Porsche coolant and distilled water. (Please use only Porsche anti-freeze rather than the cheap, though identical appearing pink stuff from Audi. Porsche spent major $ having Zerex develop that formula, not worth saving a few dollars on IMO)

As others have mentioned, the res tank is notorious for developing leaks. It's a bit fiddly to get in/out but not a bad bet to replace it. Any staining around cap/tank junctions, seams, line/nipple junctions etc could be a sign of a hairline crack.

The experts will have other ideas I'm sure.

Cheers
Mikey

 

that was excellent.

add: i always keep a proper 50/50 mix. important. i think.

 

Actually, per the handy dandy Porsche anti-freeze jug which I'm holding in my formerly nicotine stained fingers, a 50% ratio protects to -34 deg F and boil over to +265 deg f. That is 5 liters of water to 5 liters of anti-freeze. However, if we go to 6 liters of antifreeze to 4 liters of water, a 60% ratio protects all the way down to -62 deg f (!) and boil over to +270 deg f. So IMO, while the extra antifreeze costs you some shekels, it adds measurably to your level of protection on both ends, and on a turbocharged engine, we want all the boil over help we can get.

Cheers
Mikey

 

whatever. lol. you're in gilbert, i'm in la. it *only* gets to 115+ out here. the 50/50 mix should be ok. ( great! one more thing i can obsess about ) am i running 60/40 or 50/50.. ha.. just pls dont tell me it;'s not ok to run vw/audi g12

 

I won't tell you that, but Kevin @ UMW sure will.

Mikey

 

Ya. He's the only one ha

 

great advice guys. We changed the oil about 2500 miles ago. Nice and oil-looking. Not milky at all. I have not very often seen condensation in the oil filler cap, maybe twice and it was minimal.

No regualr loss of coolant, but I will admit to just "topping off" with water when i lost most or all of my coolant, so thats probably the ticket. Would it be wise to just flush and drain the system and start from scratch with a 50-50 or 60-40?

 

yes! drain and start fresh. i would. it's too important and too easy. notwithstanding the bleeding/refilling process. esp if you've diluted the mix over time or previous owner. when i buy a used car like this, i flush most everything at purchase! unless you know the history, and who ever does.

does anyone know why we have to rev to 3krpm while filling? never asked but that is part of the process. i suppose to keep the pressure up. duh.

 

This sounds like a potential radiator issue possibly. Haven't had this issue in my tt but had similar issue in other cars in the past. One of the radiators could be on its way out or could be as simple as a bunch of debris blocking them making them less effective. Its amazing how much road debris gets in the bumper openings. To get big stuff out just blow some compressed air in there. To do a real good cleaning you have to pull the bumper.

 

agreed. only to add that a failing rad can have such a slow leak ( initially ) that it will confuse the average ( me ) owner... and yeah, then there's the debris! holy crap.

edit: just spent a cpl hours in the driveway messing with the b*tch ( new wevo semi's! every bump is felt! woohoo and all my new led's inside make it look like i could perform surgery in the drivers seat.. ..and after messing with everything,..and checking my oil level after changing it which took +/- ten mins for OP temp lol ..i lost about a .5 gal of coolant AGAIN! out of the cap on my 10 min test drive around the canyon breather locked down, no issues there. levels all good. i think i overfilled it when i replaced the rad last week, and it's finding it's equalibrium. if such a thing were possible? ( it's possible when you do s*it in your driveway in the dark ) how hillbilly is that. or worse case. another cap is in my future. i think i'll just talk all this s*it into submission...lol. sorry for the rant in the OP's thread.

car runs like a bandit though. heh.