AdamIsAdam

That is MESSED UP! Why can't they make a product that doesn't leak?!

Ahsai

Yeah, i always wonder the same but for these
- window regulator
- oil pressure sensor
- ignition switch
- headlight switch
- door lock actuator
- headlight wires
- taillight wires
- starter y-cable

wyovino

I seen reports of AOS's bad right out the box. That's a really gotcha.

MikeinBloomfield

I'd just note that reading through this thread, you have an atypical problem. Some tanks (like mine, replaced by the PO), develop small cracks that leak like the video above. Others have the cap fail (like mine), where the cap doesn't hold pressure and coolant comes out once the system is pressurized. Luckily for me, this was an easy fix.

You seem to have a cap that doesn't fit. Since its supposed to be OEM (but not Porsche) I would guess that the manufacturer intended for a different cap than Porsche supplies. Probably a cap with a different design altogether, given that the threads appear to be too short.

Point is, I would discuss with your mechanic replacing this with the genuine Porsche part and not just replacing it with the same part he gave you in the first place.

AdamIsAdam

You think the threads are too short? I'll measure them. Anyone have one handy to measure and share those numbers?

MikeinBloomfield

Well, I'm speculating. As far as I know, the failure mode for most people is not "the cap doesn't stay tight." The failure mode for the cap is that although the cap is still tight, it doesn't hold pressure. I am assuming there is something wrong with the threads or the neck of the tank such that the cap can't be fully tightened. The cap isn't your issue, since you've tried more than one.

Measuring the the number of threads on the neck may help if it's different than the Porsche part for that convo with your mechanic.

AdamIsAdam

Yea, the threads/neck are/is clearly bad. I just don't think it's too short since it gets tight, but I can go beyond if I keep turning and it slips. I'll see what the mechanic says for sure. And I'm sure everyone (both the mechanic and supplier) will want to check this issue before installing the new tank of any brand.

AdamIsAdam

I realized I never circled back here with info that may be helpful for others in the future regarding replacement expansion tanks...

I had mine done when the AOS was replaced as preventative maintenance (along with a new water pump, just for grins). Old one was not leaking. New German part was installed by a very highly respected indy. He pressure tested it and the system was fine... that is, until I got it really hot. The fluid was perfectly filled to the cold line and checked A LOT (each morning during my issues). Yet once it got really hot, it seemed the coolant would leak from the cap a little bit, and then the cap would also be able to turn past fully tightened (like a medicine bottle safety top). When cold, it was fine.

I replaced the cap, twice. OEM. Same symptoms.

Mechanic replaced the tank under warranty. Same symptoms!

We suspected that the system just might be operating normally for a system that was a little over filled (even though it's not). If over filled, once hot, the cap is designed to allow pressure/fluid to escape to avoid bursting something like a hose. That dribbles out onto the "balcony/shelf" of the tank where it runs downhill to the drain hole and out the hose behind the rear wheel like rain gutters on a house.

So what did we do? We let it naturally level off without constantly topping off the tank. Guess what? PROBLEM SOLVED. So my tank has a "new normal." It's just a few ounces lower than before (see pic) but for the rest of the summer it's been fine. And fyi, it NEVER ran hot during all of this testing.

So I don't know if something is slightly different on the new tank design (remember, two German made OEM replacement tanks did the same thing) or what, but all I know is it's fine now. Just thought I'd share.

Happy cold weather motoring.

jhbrennan

One thing I've discovered is that an "OEM" part may not be the same as a genuine Porsche part even though the OEM may be the Porsche vendor. I had both a new RMS and a new AOS fail recently that were OEM parts. Subsequently replaced with Porsche parts and no issues...yet.

AdamIsAdam

I was thinking that myself. But seems odd that the same vendor/manufacturer would make two different expansion tanks, with different specs, for the same car. On the other hand, maybe there's a reason the Porsche part cost over $600 when the other one was around $350 (don't quote me on that figure, I don't recall exactly, but it was a less for sure). I assumed that was just Porsche mark-up, but who knows. My indy said he's installed MANY DOZENS of these tanks and never experienced it, despite my experiencing it twice on my car. So maybe there's another factor at play we're not considering, some other variable.

All I know is that it works now. Dry, runs normally, etc with the "self correcting fluid level" design. lol

Paul Waterloo

I had the same conclusions as you in another thread from a few years ago. My tank was leaking and I did replace it with an OEM tank.....and it was all good after that, but I think leaving some expansion room in the tank is good practice and prevents the system from over pressurization during extended runs.

NuttyProfessor

I ordered my expansion tank directly from a Porsche dealership. They crossed referenced the tank with my VIN. I got the tank and coolant level sensor for $190.00.

AdamIsAdam

$190?!!! For a Porsche brand 996 tank? Wow is that cheap!

wyovino

Just for clarity going forward, the MK-I Porsche brand tanks are in the $600 range while the MK-II tanks are about $140..

AdamIsAdam

AHHHH! Thanks for that info.