996 Water Puddle and Pressurized Water Tank

[Jay Laifman]

On a friend's 996, he went for a short 2 mile drive and parked it at back at home. When he went back to the car, there was a puddle of antifreeze on the ground below where the tank is. The tank was below the "low" mark, but not empty. Taking off the cap 3 hours later was hard and when it was finally off, there was a hiss noise - it was either under pressure and blew out air, or under suction and sucked in air once the cap was open.

I did see a little fluid below the tank itself.

I at first thought it was a cracked tank that leaked out water. But after hearing the hiss, I think that doesn't work because that wouldn't have happened if there were leaks in the tank.

Any suggestions I can convey to him?

[Jay Laifman]

After reading a number of older posts on here, I'm starting to think that it is the original cap on the coolant tank. It probably isn't up to snuff, so coolant can come out at high pressure, but it isn't totally dead, so that it still retained a bit of pressure to cause the hiss I heard.

[FPB111]

The hiss was probably vacuum. The tank gets fried from the hot muffler right below it.
It is almost certainly cracks in the tank. One way to tell is if the water is dripping out of the cap/overflow tube onto #2 coil more likely the cap. If it is dripping from the bottom of the tank onto the frame member, tank.
That said if the part number on the cap ends in ---01 you should replace it with the latest which is ---04 I think, ~$27. If that doesn't fix it tank time.

[cdrik915]

...or water pump , classic issue around 100/120000 kilometers.

[eric523]

also would be good to search for any dry coolant residue as it may lead you to the source. If it is the cap, there is often some residue at the base of the cap or in the area immediately surrounding. You can also try topping the fluid level off when cold, then get it back up to operating temp and search for an active leak.