MrMoose

The cooling system is most definitely pressurized, and the cap in the trunk is a pressure seal.

The cap on the expansion tank in the engine bay has two valves on it. One controls max pressure and opens at ~26 psi to let pressure out when hot (from both coolant expansion and increased vapor pressure), and one opens to relieve vacuum and let air back in as the system cools back down. So while all modern cars have "sealed" pressurized cooling systems, in practice you do get some flow in and out through the overflow tank cap. My 987.2 needs a bit of a top up on coolant now and again, and it's definitely not leaking anywhere.

If you're worried about hidden leaks it's quite easy to have the system pressure tested.

TMc993

Absolutely. Removing the coolant tank cap when the engine is hot can result in burns, scalds and even blindness. This cap should be treated just like any "radiator cap" on any conventional car....If it's hot or warm, don't open it.

toma nova

Thanks for the correction and additional info.

Tom

Peter Lindholm

check the heater valve that was my problem it leaked small amounts 900000 km but one day it dripped on the floor.

Kitc2246

As mentioned the expansion tank caps tend to warp making them difficult to remove. If you remove there is a fairly sophisticated rubber seal in the cap which as described lets it overflow above a certain psi and draw in air when cooling. I periodically added coolant to my 987.2 and my 981 both which were track. Nothing major or too often, just enough to float the red plunger. In the absence of any other observable leaks the first thing I'd do is replace the cap. Somewhere there is a long thread where the cap seal is a repair part, but not commonly stocked.

burnergt4

If you're referring to the user operable cap in the rear cargo area, it's likely because the tab that "clicks" the cap into the place was broken at some point by someone over tightening it. Here's a comparison between a new cap and a busted one:




Note on the new one you can see a little ramp, whereas on the broken one the plastic has been completely bulldozed. Without that little tab providing positive feedback of when to stop turning, you'll tend to over tighten by a full turn and require a couple of crescent wrenches clamped down on each end of the cap in order to get it off again.

It's been said elsewhere in any discussion of the user accessible oil/coolant caps, but you just need to turn it until you hear a single click, like this:


Any more than that and you risk damaging the cap in a similar way as seen in the photo above.

foodbiker

FWIW, for future readers - when in doubt, just replace your coolant cap. Thankfully they're not too expensive.

I did this on my former 987.1, which seemed to fix a similar situation -- and I'm certainly keeping an eye on my 981. Again, this stuff is plastic and the internals see a lot of temperature swings. Cheap insurance and just my $0.02.

burnergt4

For those same future readers—this is the cap he’s referring to:




The one labeled is black, but some of them are blue. The user accessible one I called out earlier is far less critical than this one.