Strange Coolant Leak that vanishes after a 20 minute ride?

[bBunny]

Need help here.

My 2000 996 coupe RWD, 6MT has a weird coolant drip issue that seems to heal itself.

Last week after taking the car out for a brief run, I noticed a coolant drip hitting the dirver side exhaust tip. Knowing that this is the prime indicator of a coolant tank issue, I took the car over to my techs. The car cooled down, and showed NO signs of a leak anywhere?

After a visual and finally a pressure test of the system, we came to the conclusion that the cap was the problem ( old cap ending in 00 ). We got a new cap the following day, topped off the tank, re checked and went on to other things on the squawk list.

Today, after bringing her back out for another fun run, I again noticed a coolant leak, somewhat more pronounced coming down from just behind the driver side rear wheel inside housing. ( spot was about a foot in diameter, meaning maybe a cup of coolant leak? ).

So again, I cooled the car down, and amazingly, no more leak?

The temp guage sits spliting the 8/0 always and had only moved to splitting the 0 on the way back home. I pulled the cap and the tank is flush full of nice green coolant. I'm perplexed at this point. I live in Florida, so heat is always a concern, but our temps right now are really mild and the car isn't showing any typical signs of stress from the usual culprits?

Help always appreciated.

Yes, I know search is my friend, but this issue is just weird.

[wvicary]

There are several coolant hose junctions that could explain the intermittent leak, a close inspection should find the problem. I suggest getting this sorted asap and not to continue the drive the vehicle as you don't want to risk over heating this engine.

[txhokie4life]

Seems like a pressure test when the coolant is hot might help isolate if its a thermal related weakness.

You might even consider ziptieing a couple shop towels around some connection points to see if you can pin point the leak.

I would not worry too much about driving it. You are aware of the issue, keeping an eye on it and topping it off when

you have some of the coolant leaking.

It is possible that something suddenly gives out (like the expansion tank)

and you might find yourself unable to drive it -- so do keep that in mind.

hopefully you track it down soon.

Mike

Edited September 28, 2012 by txhokie4life

[JFP in PA]

Mike is spot on, the coolant tank sometime starts leaking only when hot because that is when the system pressure is at its maximum. You can hook up a pressure tester and run it while the engine is hot, even taking the system over the 18 PSIG normal running level to trip the leak. You can also add some UV coolant dye to the tank and run the engine until hot before looking for the leak with a black light source which usually very quickly points out the problem areas.

Mike is also correct on being very careful about using the car in this condition, if the tank or another component suddenly completely fails, it will strand you and could overheat and take the engine with it; caution should be your focus at this juncture.....

[bBunny]

Here's the update on this issue. Maybe it will be of use for others.

Your suggestion to do a pressure test at temp was spot on. The tank was also a culprit as well as the failed cap (00). Figuring that the tanks was the original, we got the correct tank ( 147- not the 157 designation ) and also changed out the hoses. During the test we also found a single drop of coolant on the water pump housing inlet/outlet?

It was perfectly straight. We think it's a failed seam on the metal? Thoughts please. For now we re sealed it with JB Weld, let is cure overnight and all seems well.

Even though Robert supposedly vacumed the top off after refilling close to 2 gallons of coolant, The tank was about an inch or so down when I got home today?

I've let the car cool, removed the cap and re topped it with distilled water. A thourough inspection underneath reveal a dry car all around ?

Only thing I can figure is Porsche is like BMW with trapped air after working on RADS etc. My old 535 wheesl had to be elevated about 2 feet in the air to burp the system.

As always, help is greatly appreciated.

[JFP in PA]

Did you refill the system while it was under vacuum (preferred OEM method), or pull a vacuum after filling the system at atmospheric pressure? If it was the latter, you may still have some air in the system.............

Edited October 4, 2012 by JFP in PA