A couple of moths ago I noticed the coolant level was down. So I added some. But I wasn't sure if that's the way the car was when I bought it. Then I noticed a couple of weeks ago that I had to add some more. I have no drops at all on the garage floor. Or any visible signs of leaking. So then I started to worry that I may have a bad head gasket.
I went to autozone and got a block tester to see if I had exhaust gasses in the coolant. It said to run test for 2 minutes. I ran test for 10 minutes, twice! Just to make sure and there was absolutely no combustion gasses in my coolant also the bulb wouldn't suck in more air indicating that the coolant system is sealed.
I have no milky residue in coolant
No steam cleaned cylinders
No steam cleaned spark plugs
No white smoke
No evidence of coolant in oil cap
No sweet smell from exhaust
The porsche dealer I bought car from did all belts, seals, water pump kit, rollers etc.
So is it possible I still could have a bad head gasket?
Is it possible that by filling the coolant tank to max when cold that some has overflowed when hot?
Below is pic before I started car today and then after a 20 mile drive.

 

Well I thought min was cold, and max is when the car is warmed up. These systems are pressurized and sealed, so if you over fill I imagine the cap lets it out. But if you are smelling nothing, maybe air in your system? How does the car run, hot?

As for leaks the valve around the exhaust of the heater core is a known culprit.

Just some thoughts.

 

Engine temp is fine. If it was a heater core problem would I have coolant in the interior?

 

Approximately how much coolant have you lost, and over how long of a period? To better diagnose a niggling issue like this you need to keep a log of exactly what you observe and when. I had a similar problem with my 944S, it would loose approximately four fluid ounces of coolant over a period of 30 days. It was driving me nuts because the temp was steady, the water pump was brand new and it otherwise seemed to be mysteriously disappearing. I used a pressure tester to confirm the system was holding pressure and a block tester to confirm the headgasket condition. Long story short, one of the hose clamps on the header control valve was ever so slightly looser than the others and as near as I could determine, allowing a small amount of coolant to weep by but only when the car was up to temp and under high throttle/high load situations. There were no leaks with the pressure tester on a cold system. Tell tale sign was chalky white coolant residue on the bottom of the hose. Hope this helps.

 

Maybe...there is a condensation drain located at the center of the HVAC box that directs any moisture to an area just forward of the shifter area.

Not sure if you had a minor leak in the heater core if the moisture would accumulate in this region.

Have you considered using a plastic tie-wrap to keep the valve closed as a means to isolate coolant flow to rule out the heater core?

 

Thanks Ramius, thanks Jay, I am not familiar with the heater core on this car. I'll put it on jacks and start checking it all out.

 

there are a couple O-rings at the throttle body also.


small external leaks can be found by pumping the system with air and spraying connections with soapy water.

coolant being released as steam can be hard to find. i found about four small leaks; the fiber washer at the radiator vent, the seam on the heater valve, the heater hose at the rear of the head and the throttle housing to intake. with no leaks, she will hold a vacuum for a month and engine temps are perfect.

draining the coolant can be a mess. i raise the passenger side a little and let it run down the batwing overnight.

 

Maybe I should go get a pressure tester.

 

yes....stant makes a nice one. my theory is that if the air can leak out, it can get sucked in, in the wrong places, during cool down.

 

Are you sure your radiator cap is good?
Weak spring/seal could be letting steam out either through the sides of the cap or through the steam vent hose.

And you'd never know that it was the problem when doing a pressure test since the cap would be off the car...

This was my fix for disappearing coolant in the past.

 

I'll get a new one and see if it helps.
So on the pressure test I assume you just pump it up and then look around for fluid escaping?
I guess if I did have a bad head gasket I would see coolant in a cylinder?
Engine hot or cold?

 

stant kit comes with the adapter to test the cap. you can test with coolant in the system but if you want to find every leak quickly, test it with air. its common practice in the plumbing/piping world.

 

I second the radiator cap recommendation. Get a new one unless you know the age of your cap, they are cheap. Also 944/968 et al are finicky regarding any air in the system. Use the bleed screw on hose fitting coming off the head on the driver's side. Crack it open and run the car up to temp. Close it only when a steady stream of coolant is coming out. Double check to make sure there is a copper sealing ring around it. Torque the screw gently as it is very easy to break. A small air pocket can make for wacky coolant levels. A bigger air pocket can make for bigger problems, which you don't have.

 

Just out of curiosity, since the coolant is flowing why wouldn't an air bubble be pushed out of the overflow tank?

 

No, not all the time. The bleed screw is at the highest point in the cooling system, where the tank is below that at fender height. That is why they put a bleed screw there. On older Italian and French cars you have to remove the tank and hold it above the engine to bleed the system. Thankfully the Germans provided the bleed screw.