[jwetering]

Skeeter - the coolant tank turns yellow and fails, they all do it. No need to worry.

The cracks start out really small, and only weep when the car is hot. That's when you smell it I bet, after a drive. When things are cool enough to investigate, the cracks close up and leave little to no evidence. At first anyway.

Eventually you will see a drip or two coming from the drivers side tail pipe area. That's because the tanks is just above it there. That doesn't mean the coolant is coming from inside the engine.

Do not panic, but your self a new tank and a new cap for $200 and if you have experience, bust out your tools. You may have to drop the engine a little to wrestle the old tank out and the new tank in. It's not a job for the beginner mechanic, frankly it's a loathsome job, but there are good DIY threads on Renntech and on Rennlist. I think I even wrote one or two.

The point though is....this is probably not a big deal. It's probably just your coolant tank. I've had two 996, both of the tanks failed.