Yet another coolant problem

[bosstucker]

I've searched to find something similar but couldn't really find anything like this among the many coolant issues our cars have :(

Car in question is an '02 C4S 6MT. No modifications other than slapping on some used PSEs (no wiring, always open).

The issue is this: it has a slow leak. Within a few days to a week or two after being topped off to normal levels (with daily driving), it will have slowly have leaked below the minimum line. There is NO evidence of any coolant leaking under the car when parked or when idling--only a little water from the AC in the front (I believe). When I top it off, it will take maybe .25-.5L, usually distilled water. The operating temp is generally 1-2mm to the right of the middle line above the "8" in "180" on the temp gauge.

One incident that occurred about a year or two ago, while waiting to put some gas, with the car idling, I heard a slight pop and gurgling and hissing noises from the back, saw steam in my rearview mirror and watched my temp gauge promptly start to rise. Shut her down and found out that she had dumped all coolant on the gas station floor. Didn't know if the tank had cracked so I had her trailered to the local Porsche Indy and they couldn't find a leak, so it was just filled up and hasn't had an issue like that since.

My guess is perhaps a faulty cap? I don't know what to do next because I can't trace the leak, seems to happen while driving with no adverse affects other than me having to keep topping it off.

My questions are:

1. What do you think the problem might be?

2. I've been topping off with distilled water, but since it's happened so much the coolant is getting progressively more diluted, should I get it flushed and replaced or should I start topping off with coolant? If coolant what kind?

Thanks for all your help guys and sorry if the answer is somewhere that I didn't see when I searched...

Edited September 24, 2011 by bosstucker

[JFP in PA]

You can have both the tank and the cap pressure tested (cheap and only takes 15 min.), the caps tend to fail more frequently than the tanks, but the tank is not immune to failure. If either, or both fail the test, they should be replaced (current cap ends in 04).

As for the coolant, Porsche OEM coolant is pretty good stuff from both a protection and longevity perspective, but it is not overly compatible with some aftermarket brands, sometimes leading to gelation and one Hell of a mess to clean out. As you note that you have been diluting the original 50/50 coolant/distilled water mix (you should always use distilled water), you are probably a good candidate for dumping the system and refilling with new, particularly if you need to swap out the tank.

[xmac]

I am still a bit perplexed as to what happened at the gas station. Clearly, something overheated but it is hard to believe the problem fixed itself. Follow this link for using a u-view 55000 airlift vacuum fill system (~$120):

logray Uview Link

Prior to refilling do a rate-of-rise check. This is where you pull a vacuum, close, the ball valve, then let the system sit for a few minutes. If there is no leak, the system will hold at -25. If it does not hold, you will then need to start checking for leaks. One clue if there is a leak, is that coolant dries to a chalky white, so look for that near connections.

I just had a thought, maybe a leak in your A/C Heat Exchange (a.k.a. Heater core)? Check this thread out: Heater core replacement

[kbrandsma]

The exact same thing happened to me two summers ago. My car was at idle and dumped a gallon or so of coolant. I replaced the radiator cap and installed a new bleeder valve and it has been fine ever since. I added additional coolant and distilled water and used the bleeder valve to burp the air out.

Edited September 24, 2011 by kbrandsma

[xmac]

The exact same thing happened to me two summers ago. My car was at idle and dumped a gallon or so of coolant. I replaced the radiator cap and installed a new bleeder valve and it has been fine ever since. I added additional coolant and distilled water and used the bleeder valve to burp the air out.

The difference here is that he has to keep adding fluid. Maybe it is just an old revision cap that is not holding pressure. For around $25, worth updating the testing/updating the cap.

Edited September 24, 2011 by xmac

[bosstucker]

Thanks guys, I will definitely check these things out. Gonna get the cap and tank tested, and get the coolant flushed too. I'll keep you guys updated.