so a couple months ago, after taking my car to the track, i noticed a lot of coolant leaking after my last run of the day. quick search turned up a possible coolant cap issue. after finding no other possible leaks and determining that the overflow was where the leaking was coming from, i purchased a new cap. Now, i had read alot about a new black cap, and blue caps are the devil etc... but i also saw that people were having trouble finding this mysterious black cap, as all the parts suppliers and even the dealership i went through had a blue cap listed as part number 996-106-447-04 for the newest cap.

fast forward to today, not a really warm day, 82*. I park in a parking lot after a very uneventful drive, and notice coolant pouring out my back end. i get it home and find that it is leaking around the cap again. So my question is, could it be the neck of the tank possible deformed or threads messed up? Or is it once again the cap? and if it is the cap, can someone tell me where to find the black one? tank is about 20k miles/2 years old and in good clear color. pictures below show old and new caps. The newer one is the brighter blue with no visible numbers.

 

Maybe the crack is around the coolant tank threads, and starts leaking when the cooling system pressurizes.

 

i will check around the tank threads. thanks.

 

If it's leaking as much as it sounds like, then I'd agree with the above poster that it's not the cap and there's probably a crack you're missing in the tank.

Did you look on ebay for the cap? Because there are quite a few listed on there:
http://www.ebay.com/sch/i.html?_trks...at=0&_from=R40

The interesting thing is there are caps of both colors with the two different designs you posted above. If I wasn't so lazy I'd walk out to the garage and check what my cap looks like. Maybe tomorrow!

 

i hadnt checked ebay. i just stuck with the popular distributors. I'm never sure what would show up when i order from ebay. ill make sure to check it out. thanx

and since both shades of blue, PLUS the black cap are shown on ebay... does that mean all 3 are appropriate caps? and how would i check the tank for leaks, especially if the leak is suspected in the threads?

 

I have a horrible feeling that if you dont find a crack in the coolant bottle you could very well have a head gasket on the way out. That would be pressurising the bottle and pushing coolant out the pressure relief valve in the cap.

 

yeah cause isn't the cap out of the coolant, meaning it's not even touching if the level is correct? Your tank would need to fill up for it to leak.

I may be saying something stupid though, just thinking out loud.

 

The water system is always pressurised when the engine is running at normal temperature. Its the pressure that increases the boiling point of the water so the coolant doesn't boil away. The system pressure is governed by the pressure relief spring in the cap. for eg 13 psi . i cant remember what the 911 pressure relief is. The expansion of the fluid causes the pressure to rise and as the coolant cools it contracts and the pressure drops. when the coolant expands it compresses the natural air pocket in the top of the bottle, but will never be vented out the cap due to the design of the whole system. however when a head gasket fails it pushed the system pressure above the design limits and the relief in the cap vents of , firstly the air in the bottle closely followed by coolant untill enough pressure/water has been released.
When the system then cools down, your bottle will show a loss of coolant.
So if the bottle has a crack oa the top near the cap it could well be venting off the natural air pocket in the bottle as the water expands and eventually coolant will be pushed out as the water level rises to the level of the crack. This will also mean the coolant could boil at normal engine temp making matters even worse.

 

Is there anywhere to look to see if its the head gasket? Is this a known failure?

 

Here is a very simple thing to check - this cap has to be cranked on very tight - tighter than you would think is necessary. It is very possible that you just haven't cranked the cap on tight enough and the pressure is leaking out through the threads.

 

What about a thermostat? I had a similar issue on a former ride and the thermostat was stuck in the ALMOST closed position.

 

OEM cap has the part number that ends in the number 4 on the top and is identical on the inside to the previous version wih the last digit of the part number being a 3. Have never seen any OEM Porsche part, short of industry standard fasteners, without a number on it.

 

Did it show signs of overheating ....gauge etc? The OP hasn't told us if he is experiencing over heat problems. That would be a good thing to know. Perhaps he will post the answer.?

 

i would have to check that.
so my newer cap, the one on the right that has n numbers, is probably not an OEM part? it shows the same part with matching part numbers on the ebay items.
no signs of overheating, no change in the way it drives. Once the coolant overflowed and purged all my coolant out of the overflow, my low coolant light came on and my temps climbed a bit. I dont know the exact temp, but on our cluster gauge, the needle was sitting about straight thru the "0" of the number "180". So maybe halfway between the 180 marker and the next (200? 210?) marker. Not bad i dont think, and they came down oce i got driving home and air moving.

thoughts? and thanx guys. I filled up with coolant today to just a touch over the minimum line and no issues. Now that i think of it, i think i had OVERFILLED when i topped off after i replaced the cap. Could that explain it?

 

All I can tell you is that the new cap I purchased from Suncoast Porsche a few weeks ago is Blue, has the correct part number embossed on the top and the inside pressure relief valve has the same screen on it as the one on your older cap. No way your cap is an OEM Porsche part.
As for the black caps, some of the early caps were black with a part number that ended with the number 1. If you can, return the part you bought and buy the proper cap from Porsche. Suncoast sells 'em for around $25 as I recall. Once you get it, make sure the coolant level reads at the min mark with the engine cold. I hand tighten the cap then take a plumbers strap wrench to it for another 1/4 turn . If this doesn't solve your problem the system needs to completely purged of air with a UVIEW Airlift tool, or equivilent.