C4S massive, yet temporary, coolant leak

Hi, I have just bought a 53 plate C4S, however not a full day in to owning it I've managed to have my first problem. Stuck in very slow moving traffic for 20 minutes at midday today, being a very nice sunny day, a couple of people told me that the car was leaking. Sure enough, there was a nice trail and a big puddle of coolant streaming from the rear passenger side of the car - probably a couple of litres at least, no idea how long it'd been going for. So (and with much gratitude to the 997 Turbo owner that offered assistance) I moved the car on to the verge and waited for the AA. I was thinking a blown hose, or the tank having developed a crack or something like that. However the wierd bit that I can't understand is that the AA man topped it up with water, put it up to 5 bar pressure, and the system held. I then drove home (very cautiously) and checked the coolant level again, and it all appeared to be ok. Has anyone seen this before, or have an idea what could cause a "one off" kind of water drop like this? I'll be contacting the garage I bought it from tomorrow, but it'd be nice to know how much trouble it could be to fix. thanks, neurotoxicity

Sounds like the Air con dumping it's dehumidified water out, quite normal! You see, when hot, the water wouldn't just be trickling out, it would spurt steam instead! That wasn't coolant my friend, fear not. Aircon can produce a fair chunk of water, and alarm people... :thumbs:

Hey Indy, regrettably the aircon was off (cab, topless) and when we checked, the coolant level had dropped. To the point that I'd guess that the AA bloke put a good couple of litres in before it got to the "min" level. Very strange indeed.

Without doubt it is the expansion tank for coolant. A little more research on this forum will confirm all your worries. Not a massive job but a total c@nt to remove.

Coolant tank cap would be my guess. Very common problem. Porsche are on the 4th design revision too, so probably haven't cracked the problem yet!

had exactly the same symtoms, large puddle, top up, nothing until car gets hot again in traffic then large puddle, was diagnosed as coolant tank and cost about £350 to fix with new (inc new cap and release valve) and fitting apparently the plastic cracks but only leaks under pressure and heated conditions, when cold will hold pressure cheers tim

had exactly the same symtoms, large puddle, top up, nothing until car gets hot again in traffic then large puddle, was diagnosed as coolant tank and cost about £350 to fix with new (inc new cap and release valve) and fitting apparently the plastic cracks but only leaks under pressure and heated conditions, when cold will hold pressure cheers tim

the plastic on them doesn't crack they just seem to split along the seem where they are put together...

Hi Don't want to worry you too much and its hopefully just the cap or tank but it could also be the early stages of a cracked cylinder bore. The pressure from the explosion in the cylinder leaks through the crack into the water jacket and increases the coolant pressure beyond which the system is designed to holda nd operate at. It eventually gets worse and other symptoms develop. In the early stages it can seal up and is more of an intermittent fault with other weaker areas in the coolant system sometimes failing in the run up to the pressure getting so high it causes a more permanent fault. Repairable but expensive and requires and engine rebuild & repair (we've got 3 in the workshop at the moment). I've an old customer which calls me the grim repear - I wonder why ! Fingers crossed that its nothing too serious. Grant

Not necessarily, I've just had a rad split and the water poured out from under the front PU, no steam at all. The Orange yellow colour gave it away. TB

OK, information recieved: Seems likely to be cap then, as coolant loss appears to be from low pressure side of system, and if it was checked to be leak free, the cap would have been removed at the time! Head gasket would usually have provided lower, or higher pressure with engine running...not 'no loss or gain'

thanks for all of the replys guys - it's with the local OPC today; from the way that the service guy was talking, it's not exactly the first one that they've seen! The system was checked by the AA only at 5 bar (naturally, without the cap being on), so if the system can easily hit 16 bar at high temperatures that test didn't really mean too much. Grant: hopefully the OPC techs are aware of that *fingers crossed*. Otherwise I could be in for an "interesting" ownership! p.s. thankfully the selling garage have indicated that they'll be no problem with them footing the bill. I'll only sort out the sigh of relief once that's all settled!