But I estimate that ...

Pedro, Thank you for your in-site about the coolant filler cap for my 1999 911 C2 Cab. There had to be something happening when I noticed the coolant level was down in the tank and there were no visual leaks anywhere. The tank was down ~500 ml of water (distilled water added.) This might be a reason for my car's overheating tendency in stop-and-go traffic.

The original cap # xxxxx.00 would hold coolant with no sign of leaking, but when I was in the stop-and-go traffic, steam pressure (coolant) would build up and escape, eventually show a loss, as mine did. The newest Porsche cap is now numbered xxxxx.04 and lists for ~$24.54. I think this is something all Porsche owners with older cars need to know; an item seldom remembered because it is so simple and right in front of you in the engine bay. I hope this is helpful to other Porschephytes.

Thanks again!

...on the early 996s and 986s are the same part number and all need to be replaced if you still have the original cap.
They tend to lose their pressue-holding capacity and will leak water vapor.
All of them came with xxx.00 caps and Porsche had to modify them 3 more times.
The latest version, as you note, ends in xxx.04 and that version seems to work very well.
Happy Porsche-ing,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

I replaced mine and no more leaks - for about 2 months. I had a nice pressurized system during those 2 months until the tank cracked, lol. I should have considered the old cap as kind of a primitive pressure release valve. I bought the tank but chickened out on doing it myself once I saw how hard it was going to be. When I took it to the local Porsche shop in Little Rock the guy said it was going to be the third one he'd done that week. I guess he's pretty good at it by now.

... it was your old cap that allowed air into the system which eventually was what cracked the reservoir.
I have always believed that whenever there's air in the system eventually the reservoir will crack.
Always make sure whenever the system is compromised that you bleed out all the air.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna