HELP! Big coolant leak!! - 986 Forum - The Community for Porsche Boxster & Cayman Owners

I've just parked up in a supermarket and turned the engine off. Then I heard a sound that sounded like water gushing. Looked under the rear to find coolant (I think) spilling from the car: I took a quick look where it was coming from, and it's coming from this pipe behind the rear right wheel (US passenger, UK driver): What the hell is going on? I'm sat in the car waiting for a recovery truck to take me home as I'm worried about starting the engine. Is that pipe supposed to be connected to something? I'm 90% it's coolant but it could be brake fluid. But then again, the brakes feel completely rock solid here with the engine off, so it can't be that?

It looks like either the coolant tank cap has a leak, or there is a leak in some portion of the tank. That tube in the picture is where the coolant tank drains if fluid leaks out in the top portion.

So the top portion being where the coolant and oil cap is? It was wet around there when I opened the boot.

Pop the trunk and see if the level is normal?

It's not, it's very low.

The hose is the Coolant tank overflow. Connected to side of tank behind carpet but if it was wet around cap could be cap is old version and has gone bad, loose cap. Could be over filled as well

I haven't touched the coolant since I've had the car in November. The cap doesn't appear to be bad though? It could it still be bad even if it's visibly fine? Thanks for the quick replies guys, I really appreciate it. I'm still waiting for a recovery.

I believe newer cap ends with 04. Yes like most things it could be bad but not viable to the eye. Dried/damaged rubber o-ring. What was the Temp gauge doing as you drove?

996.106.447.01 That's the cap number. I didn't recognise it doing anything, it literally started to leak when I reversed into a car park space.

If it was the tank that was cracked, would the boot carpet be wet? Mines dry, it was just around the lid that seemed wet.

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You have an old cap. Replace with one ending in .04. Yes, if tank is bad it will leak into the trunk. Since yours in in the fill/drain area it is most likely the old cap or could be the release valve. I'd replace the cap.

Right okay. Could you give more information about this release valve, where it can be found and what I'd have to do to replace it if it's bad?

That is old cap version Under my trunk carpet is a foam floor insert so my carpet never got wet when my tank went You would need to lift all that to see if coolant is laying around

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Ahh. Pull the oil cap and coolant tank caps off. Then pull the flat plastic trim plate off, May need a flat screwdriver to help lift one corner. Underneath that cover is a wire bail that you lift to release air in the system when filling the coolant system. Search filling the cooling system for more info. Will need to be done with the loss of coolant in reservoir.

Pull up plastic cover that sits on top of coolant tank but under filler caps. Then you will see the purge valve mechanism. A metal handle that tilts to keep valve open surrounded by screws

My 98 has intermittent issues last summer with belching coolant out of the overflow. I opened the purge, carried distilled water for a week, and eventually the air worked out of the system. I had my water pump replaced and there was an air pocket hiding somewhere. The overflow issue was intermittent, and didn't manifest immediately afterward. Try running the purge open for a few good heat cycles.

Interesting! At least it's not a huge issue. The water was really gushing out of he overflow for at least 10-20 seconds before it started to stop. Would that still be down to a bad cap?

Yes. The cap is probably leaking - when the coolant cools the leaking cap allows air into the system. When you restart the car, the air expands and forced coolant out through the overflow - which is what you have. 1) Replace cap as suggested above. 2) Top up coolant with distilled water / Porsche coolant 50/50 mix. 3) Open the purge valve D shaped lever for at least 3 x heat cycles of the engine or for a few days. This allows air to be expelled. 4) Top up the coolant tank each morning as the level will drop as air is expelled. 5) If the air is getting to the system because your tank is cracked, you will see moisture under the carpet in the boot.

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Thanks for the info. Can you tell me how to do this, and how it works?

When you remove the coolant cap and oil fill cap, prize up the plastic cover and underneath there is a round valve with a chrome D shaped lever attached. Just lift the lever into the vertical position and leave it there for a couple of days or 3-4 complete heat cycles (cold to full temp). After each run and then cooldown (say overnight) you will probably find the coolant level has dropped as the air is purged. Top up as required with the correct mix of correct coolant. If you are still not sure, use the search function for pictures - it works quite well believe it or not....