First off - I am not complaining - this car has been nothing but really good to me since the day I bought it. It's just a story.

Bought the car in early 2009 with 120k kilometres on the clock. It needed an expansion tank but nothing else. No big deal I had replaced the tank in my previous 996 so knew the drill.

8 years later another 120k kilometres later and that new expansion tank is leaking as well. It still looks white and new, but it's wet all along the bottom and coolant is dripping from my DS muffler tip. Hoses in the area are clean and dry.

I guess the next tank will need replacing in 2025 when I roll to 360k kilometres.

 

At least you can do it yourself

Was it a genuine or aftermarket part?

 

Could it be the cap?

 

Maybe I'll order my new tank and cap now for later.

 

It was a Porsche OEM tank at the time, and I upgraded to the newer style cap as well. Neither were particularly expensive then and it looks to me like the price has gone down since then.

I'm certain it's not the cap this time - there is a lot of fluid on the bottom of the tank, but no signs of coolant around the top.

It is a valid question though...I flushed my coolant prior to the driving season, and replaced a coolant hose and the plastic fitting that connects the cooling system to the AOS about a month ago.

That work all looks fine - which means that this failure is a "coincidence".....I know it smells fishy to me too.

 

Tanks are plastic and have welded seam along the back side that eventually splits and leaks with multiple heat cycles. Common issue on BMW and other cars too. 8 years is not bad ! My tank finally blew - but after pulling into my garage at least - and not on the freeway. There are a lot of other plastic parts used for cost/weight that will eventually fail - so closer car gets to 10 years - you are going to have more of such problems. Too bad tank is such a fiddly job on the 996.2.

I dont mind parts like that failing if they are cheap and easy to replace ....check some of the other plastic coolant connectors and the hose condition while you are in there

 

Is the relief valve on the system working properly? It should lift up to relieve the pressure in the system. You should be able to lift it manually to test that it does in fact work. Mine is a 99 with the original tank and cap. When I change the fluid in the system, I leave mine in the up position to burp the system of air pockets. Over pressure could possibly split the plastic tank if the relief is sticking in the shut position.

 

I wouldn't, they generally start leaking gradually and you can order one when you need. I think I drove mine for over week after the leak developed. I checked every day and may have topped off once or twice, but probably didn't need to.

You're gonna jinx yourself buying parts thinking that one of the 500 modes of failure aren't going to strike first. Only half joking...

 

The deed is done - nice 3 inch crack on the wall of the old tank...plastic was hard and brittle. I guess 70,000 miles or 120,000 kilometres is the lifespan.

The job wasn't bad....I tried (again) to do it without doing a partial engine drop, but no dice. The fuel rail is very much in the way. If you are doing this job...just start with the engine drop.

Actually start with removing the air box and aux air pump. The nut that fastens the air pump to the side wall is also the (only) nut that holds the coolant tank in place. The bracket does most of the work.

Then siphon as much coolant out of the tank as you can....and then unclamp nd remove the three hoses.

Then unplug the level sensor and very carefully twist it and pull it straight out. Delicate piece - put it somewhere safe.

Dropping and reinstalling the engine was child's play

1) Put a low profile floor jack under the engine - there is a nub just at the back edge of the sump - you'll see it..
2) Jack the engine just until the car starts to lift.
3) Undo the big nuts on the bottom of the motor mounts. I have RS semi-solid mounts so there's a big bolt goes through the centre of the mount, but the stock hydraulic mounts have a large threaded stud protruding out the bottom.
5) There's a plastic clamp holding the main aluminum pipe from the radiators just under the coolant tank - easy to see - undo that.
6) lower the jack. In my case I let it all the way down - probably gave me better part of six inches.
7) remove the tank - inspection of the new tank shows how the tabs fits into the bracket. Basically pull it sideways an inch then drop it, and magic it out of the too small hole it's in - kind of like childbirth.

Install is reverse of removal.

Don't let this job scare you - it's not that bad.

Also don't do like me and forget to reattach the coolant return line. I think I pumped about 7 litre of coolant all over my engine bay.

Three hoses and one level sensor!