Help with this coolant leak (w/ pic)

Before I get murdered, let me preface this by saying I searched before I posted this. I was buried under an avalanche of unrelated posts and managed to dig myself out. For about three weeks I have smelled a slight whiff of coolant, sometimes while driving, sometimes after I get out of the car. Coolant level dropped in barely noticeable increments. Still OK level after all this time and driving. Never saw anything underneath the car. Finally got out after a long drive this AM and located the problem: https://i.imgur.com/pUPyMS7.jpg You can see dried coolant residue on the top of the tank. The black doodad on top (relief valve? I have no clue) is weeping at the bottom right (partially blocked by the purple cap due do my crappy picture taking skills). What's the fix for this? A new gasket and/or Permatex on the doodad? How does one remove the doodad? Or am I ***** and do I need to replace the entire tank? Thanks! Dave '00 C2

Quotes source post: 11758565

That doodad is the bleed valve. They generally do not leak thus I would say in this case that doodad is not the source of the leak. More likely the cap is the source of the leak. Get a new cap. A cap ending in part # 02 or 04 is one you want. Clean the tank where the cap sits and where it threads onto the tank. Using hot water thoroughly flush the residue away so the tank and the doodad are free of any anti-freeze residue. Top up the tank -- do not overfill! -- with distilled water and confirm the level. Note accurately the level. Then install the new cap properly and drive the car around until the engine is fully up to temperature. Leave the A/C off. Back home raise the RPMs to 1000 or 1200 and hold until the radiator fans come on. Shut off the engine. Carefully open the engine compartment and observe if any signs of fluid/vapor appear from the cap or from around the doodad. Be careful. The engine is hot and the coolant will get hotter and develop more pressure. You do not want to get your face too close and risk getting a face full of hot coolant should something let go. If you want make a tent of alum. foil and place over the cap and the bleed valve. Every once in a while look at the underneath side of this foil tent for water condensation. If you see any there's a leak. Probably not the new cap. Could be from the doodad. Check for any wetness around this. But it could be from a split or crack of the coolant tank. Often this is underneath the tank along a seam. You need to also make arrangements to when the car is cooler to get the car in the air and carefully inspect the water pump for any signs of a leak. It won't account for the residue on/around the tank or the bleeder valve but it can account for the odor of anti-freeze.

Try a new cap like Macster said first. If that doesn't fix it I would suggest replacing the whole tank instead of replacing the o-rings under that relief valve http://www.autoatlanta.com/porsche-p...section=105-20 . They are available but I think it's a waste of time.

Thanks for the info - got a new cap on the way from Suncoast and I'll clean it up, install, and keep my fingers crossed.

"Then install the new cap properly " New Cap and...^This^... Ask me how I know It's pretty easy to put the cap on crooked...

Funny(not so funny to me) story about the doodad: So, I had a leaking coolant tank and I thought I'd tackle the repair myself even though many people talk about what a PITA it is to replace on a MkII 996(it is). So, I spend a few hours on a hot July day swapping out the tank, replacing all the relevant spring clamps with SS screw hose clamps and commence to bleeding the coolant system with the vacuum kit I bought. Only, I can't pull a vacuum on it no matter how much I try. Then I try leaving the pressure valve open thinking maybe I can burp it by taking a drive. All I get is a flashing CEL and a flatbed tow back to the house from AAA. I dick with it some more and finally tow it in to my local indy to have it fixed properly. Long story short, the tank I bought had a bad diaphragm in the doodad and all my efforts were a complete waste of my time. And, no, you can't repair it.