Too much pressure in coolant tank

[bglz42]

I have been struggling for over a year with an issue with my 01 Boxster S Tip. Condensation under trunk lid over the coolant cap. I am on my 6th 04 cap. Never overheats. No water   in oil or oil in water that I can detect. Level stays pretty consistent. Pressurized tank to 20psi for 24 hours. Pressure tested cap, pops at 20.5.

 

Getting desperate, I left the pressure gauge on the car and started it. After it warmed I got 20psi, (which is enough to pop the cap valve apparently.)

 

Again, the car does great even in Texas heat. It just vents through the cap... any ideas?

[JFP in PA]

I have been struggling for over a year with an issue with my 01 Boxster S Tip. Condensation under trunk lid over the coolant cap. I am on my 6th 04 cap. Never overheats. No water   in oil or oil in water that I can detect. Level stays pretty consistent. Pressurized tank to 20psi for 24 hours. Pressure tested cap, pops at 20.5.

 

Getting desperate, I left the pressure gauge on the car and started it. After it warmed I got 20psi, (which is enough to pop the cap valve apparently.)

 

Again, the car does great even in Texas heat. It just vents through the cap... any ideas?

 

I'm away from the shop at the moment, but 20PSIG seem a tad high for the cap to "pop"; if memory serves, it should release at just over 18PSIG.  While this small difference could just be differences in test equipment calibration, the larger question is why does the car hit the venting pressure, which is not a normal occurrence.

 

If you are absolutely sure that the car is holding 20 PSIG, I would start looking at two things:  Leak down values, and the evidence of combustion gas in the cooling system (requires a specialized test kit):

 

[Papp_e]

Mine did the same. Thought I needed a new cap after getting the newest rev just a few months prior.

It was the coolant bleeder assembly. The neck which is secured using 10,000 hex bolts and connects the flippy handle to the tank itself had a crack along the inner seal. Pelican sent me a new assembly for just the bleeder valve and all is well.

[bglz42]

Thanks Papp_e! That solved it! Bought a new assembly from Pelican. I guess I was getting a false reading from my pressure gauge...

[Hilux2400]

I had a similar problem 2 years back on my 996.    One of the holding down screws had rusted through due to a coolant leak. Eventually, I replaced the tank and the bleeder assembly.