2nd Failed Coolant Expansion Tank on 2000 996 C2 Rebuild

I know these coolant expansion tanks are a known issue on these cars and prone to failure. I'm on my second one now and I've got some questions for the class: Car is a rebuilt 2000 C2 6-Speed. New build has around 11k miles on it and was done by a very reputable shop that's in-network for LN. It's an LN-style 3.8 with Nickies/Mahle pistons/Carrillo rods/IMS Solution/Heads done by Len Hoffman. Running a 3.8S oil cooler and a 3.8S air box. Car runs well, makes good power, and has no visible leaks and has never needed its coolant topped. Nothing in the oil sump when we dropped it to add an X51-style baffle last month and a clear oil analysis for everything other than elevated aluminum (another problem we're tracking down now, but the theory right now is it's still maybe breaking in those pistons slightly and we'll see what the numbers look like after another 3k miles). The car is running hotter this summer then when I first got it back after the rebuild last year. We're having a lot of 85-90 degree days and when I'm tooling around town under 60 mph with the AC on, the coolant temp dash gauge will clear the 0 in 180 and land JUST to the left edge of the dash that indicates the final portion of the gauge/the overheating zone. Not a ton of sitting in traffic or idling, but I keep my revs around 3200-4k when I'm cruising locally. It comes back down to the right edge of the 8 in 180 when I'm on the highway pretty quickly and it has never crept beyond the last dash on the gauge before the 250 degree range. Never had an overheating light flash on the car. The radiators are the original units and have 72k miles on them. They have been cleaned and inspected and seem to be fine. The high speed fans do not seem to turn on until it is at that far point to the right of the 0 on the dash gauge, which the secret HVAC coolant temp readout correlates to as 108 C, which I do not like at all. The fans do work at low speed and are both pulling fine when I've checked. The engine builder that did the car is going to check with a durametric and an infrared tool to see which of those temp gauges is closest to accurate, but agrees it is running too hot around town. We replaced the water pump and all of the hoses with OE Porsche parts with the rebuild and it's running a low temp thermostat from LN. The fan for the engine compartment only seems to run when the car is VERY hot and doesn't stay on when I shut the car off. My first NEW coolant expansion tank sprung a pinhole leak last Aug. It was on the inner right side (facing INTO the engine) and didn't appear to be on a seam. I chalked it up to them just being a ****ty part and it was a really weird spot to spring a leak, so I assumed it was just a bad casting. Part number from the first one we replaced with the rebuild was 996 106 147 56 and the cap was 996 106 447 04. It was the black cap. Car was definitely still running a bit hot on summer days, but not like it has been these season. I drive hard on the street, but it has never been tracked. It was replaced under warranty and I don't have the part number for the second one, but I'm assuming it was like-for-like as my mechanic had to have exchanged it as faulty. The second one has been bone dry all year and even with the car running hotter, it seemed alright. Had it out for a 30 min run on a 90 degree day last week and revved it out pretty hard a few times and found a dried puddle of coolant on top of the tank when I came back out in the morning. No intermix/nothing sketchy in the coolant itself and not a huge leak with anything dripping to the floor, just a bit on top of the tank. Cap was sealed fine, so the theory was the pressure release valve puked some coolant up when I mashed the pedal with the car hot -- which I've been told is not abnormally on very hot days. Cleaned it up and drove it again for a few days (including hot days) and no new coolant pooling, but brought it to my tech just to be sure because I wanted to know where it came from. They pressure tested the system with the car cold and it seemed fine. I went and drove it around for a half hour to get it up to temp (it was another 87+ degree day) and check it again before heading home and got stuck in traffic, at which point the temp hit that high mark to the right of the 0 on the gauge again. I drove it back to the shop pretty gently and found a much bigger leak of coolant from the pressure release valve. It was exiting through the routing tube down to the left tailpipe this time. My tech says that pressure release valve is what isn't holding pressure now and we have to replace that/the tank again before pressure testing the whole system properly, which is fine. My questions are: -Could the faulty pressure release valve be the REASON the car is running hot, or is it most likely a symptom of the car running too hot? I do not just want to throw another coolant tank on and have the car keep running this hot and eventually break another a third one. -If the OG radiators seem to be fine/show no signs of damage or leaking and the new water pump and thermostat are ok, what else could be causing this thing to run so hot? -I'm considering upgrading to the CSF Racing radiators, but I don't want to just throw upgraded parts at this thing if it's running too hot for another reason. Basically want to figure out of they're the root of the issue or if there's a bigger problem here. The CSF model that says direct drop-in is 7044, but they also make the 7055/7056 for the Turbo cars. Will those fit on a .1 Carrera and is there any benefit to using the Turbo units? Thanks!

The latest Porsche OE coolant tank cap is blue. And it should have 04 on it. Get a new cap from Porsche. See here http://www.autoatlanta.com/porsche-p...section=105-20

Quotes source post: 20135552

I'll confirm the next one is genuine Porsche. Can you tell from the photos if the tank itself is a genuine Porsche unit? Again, the numbers on the original rebuild invoice all match the OE Porsche numbers.

They just don't make "plastic" like they used to ...

Quotes source post: 20135700

Why is it so hard for everyone to get this ****ty little plastic tank right and do they just fail on their own or are they generally a victim of an engine that runs too hot?

Mine was running hot in the summer, worse than yours, until I replaced the radiators due to a leak. Now it runs no hotter than mid-0 on the 180, even in the sumner with the AC on, in traffic. I know the high temps (and associated pressure) stress the reservior but mine was replaced a few years prior to the radiators and has been fine for four years or so.

Quotes source post: 20135774

Was the leak visible/dripping beneath the car or was it hidden with the radiators and bumper installed?

Quotes source post: 20135754

It's not that hard ..BUT ... the ones who already have a replacement product for sale are making $$$ ....and IF someone were to make an Ultimate-Indestructible-Lifetime one for $500-$600 if would probably just give more incentive to justify the Tightwads to buy the cheapest one available.( and hope for the best or do it many times )......and the Creator who spent a year ( or more) setting up for production would probably only sell a couple dozen ...That's just the way it goes.....

As DBJoe996 said, get the blue cap first. I think your current cap is getting weak and isn�t holding pressure well. Also, I recommend you do the �high-speed fan hack�. With the high-speed fans activated at a standstill, I�ll hold the throttle at 3k rpms so the water pump will circulate the cooled coolant and bring down the engine temperature. The water pump doesn�t rotate fast enough at idle to manage the temperatures well. It�ll be worse if you have an underdrive crank pulley - which I was interested in using, but ultimately decided against for this very reason. I also try to avoid traffic jams in summertime. For both my sanity and my engine�s sake.

Quotes source post: 20135777

Very visible. The low coolant light came on while I was driving home from work. I made it home, but just barely, before it was critically low on coolant. When I got home I saw the coolant leaking out from the left front of my car. Luckily, my mechanic is at the end of my street, 1/2 a block away.

�West Germany� on the cap is a good indication that it�s aftermarket.

Quotes source post: 20135444

Your above quote shows the radiators can't exchange enough BTUs any longer without the increased air flow from hi way driving. Over time (20years for sure) inside the radiator internal core coolant passageways form corrosion/mineral buildup. It doesn't take much to hamper heat transfer.. Hence the reason to use distilled water if mixing up a coolant concoction. Distilled water without a lot of mineral content like tap water will slow this corrosion/mineral buildup. Once any tap water is used sometime in radiators life, just a matter of time till a coating of white mineral build up hampers heat transfer.. But, Just the erosion/corrosion from 20 years of coolant flow will subtract from the btu transfer rate of the radiators... Change out your radiators, preferably to new all aluminum high capacity ones. But even a new set of oem will work to keep your around town temps noticeably more in control... jmo

That expansion tank cap is an OEM from Blau. It is the correct -04 part number but it isn't working. You can see coolant has seeped out from the pink and white residue around it in the first picture. Get the Porsche cap. It is $6 more at Pelican, which also still sells the Blau.

Replaced the tank and got the correct cap and the car is still running hotter than it should. Not TRUE overheating, but no significant change when idling or putting around town. Going to try the CSF radiators and see if it makes a difference, but otherwise, I'm stumped and my mechanic thinks the only other thing could be a blockage in a line towards the front of the car as the hoses in the engine bay were all replaced 11k miles ago. I'm going with the CSF 7044 units, but just to double-check, the 7055/56 that fit on the Turbo/widebody cars doesn't fit a C2 without mods, right? And would there be a benefit in running the Turbo-sized ones if they do fit easily?

Have you checked coolant temp via OBD2? The gauge may be off. The CSF radiators are no better than new OEM radiators. They may be better than 20 year old radiators. The Turbo radiators are about twice the size of the Carerra radiators. The Carerra radiators look like toys in comparison. I have read where someone stuffed Turbo rads in the Carerra bumper. Don't know how much work it was.

This the info I got from AI on CSF turbo radiators fitting C2. myself I am thinking of doing two CSF turbo radiator but no center radiator in 04 C2.. porsche 996 turbo radiator installs in 996 carrera - Google Search

Quotes source post: 20141861

Which CSF radiators are you referring to? There is a OEM replacement (3564), and a larger/thicker double-row core version (7044).

Anecdotal story from a few years ago... Had a leaky driver side radiator on my 996.2. Didn't want to put another plastic crimped on side tank oem type radiator as thats where it was leaking from, the faulty crimp on plastic side tank. Never liked that plastic tank to alum core crimped together construction. Didn't want to spend C$F money, so opted for a amazon all aluminum high capacity 2 row radiator for $97 at the time, now $150. Radiator shipped in a couple days, was impressed by the perfectly fitted foam padded box it shipped in. Also the nice tig welds and seemingly quality build of this inexpensive radiator. Well, was not so impressed by the not threaded bolt holes to mount the duct or maybe it was for the ac condenser, don't remember exactly which..? They were not threaded. Could of tapped them out, but found some perfect fit self tappers.So used some self tappers, problem solved. Problem 2, well, the posts that go thru the rubber grommet mounts had no groove for the clips. So took my die grinder out and made a groove. Problem solved. Seems these cheap radiators missed the last few steps of production maybe..? Everything else fit perfectly. Ya, its a little work fitting this rad, but to me at 1/3 the cost, well worth it so far... Got the radiator in and all air bled out. Just changed out this 1 oem leaky radiator with the 20 year old oem rad still on the passenger side. To my surprise, now, with Amazon $97 full alum new rad, in the middle of a S FL hot summer, dash gauge temps were lower than ever before, never going over middle of the 0, even sitting in bad traffic. Before, with oem rad, would go well past the 0 and then some in traffic. If stuck in traffic some times wondered how high it would go. Seemed if stuck in traffic long enough it might overheat. Found it interesting that just 1 new radiator would be able to remove enough btu to now allow the cooling system to keep up with demand. Been good for a few years now. The left side rad seemed so quality made (and cools great) other than bolt holes not being tapped and no clip grooves, was thinking of maybe getting the right side, passenger side rad for a set. Or just in case of it being needed in the future, but Amazon only offered the left radiator, not the right side. Very Strange... The vent nipple is welded in, ok not a problem its set up for the left side only. Was thinking if needing the right side rad, of drilling a hole, welding in a 1/4" boss, tap it with a npt nipple, plug/cap the other nipple not being used, and have a right side rad as all other things are identical.

Quotes source post: 20142208

Same size units in same new condition will have the same cooling efficiency (very close if not identical). Larger or thicker units may be more efficient - or not, some "high performance" rads have the fins so densely packed they don't let much airflow through. Comparing a new rad to a 20 year old one the new one will be better. The fins get clogged with dirt and it's impossible to get all the dirt out.

Going with the 7044 dual core units. They're the CSF "racing" model, not the like-for-like OEM model. My car is not FULLY overheating, just running hotter than I want it to around town on hot days. Apparently the dash gauge shows around 10 deg hotter than the coolant tank does with an infrared scanner.

Anyone replacing their coolant tank with "OEM" will be doing this job every year or two. Ask me how I know. You absolutely need to spring for a Genuine Porsche tank. Porsche tanks don't come with a cap. A sure sign that your tank isn't a genuine Porsche part is if it come with a cap. This has been discussed many times here. You're going to get sticker shock when you see the price of an MK-I tank, but you'll need to bite the bullet.

MIght be worth checking that you're not getting exhaust gas into the coolant system. Does the bail on the tank stay up after the car has cooled overnight (i.e. coolant system remains pressurized)?