Consuming coolant
 

2010 Carrera S Rwd Cab Manual 144 K miles

In December (about 5K miles ago) I added a quart of distilled water to top off the coolant.

It just needed a half gallon of DI water to top it off!

Questions:
1) Should I keep topping it off with DI water and call it an old car?
2) Should I start topping it off with Porsche antifreeze and call it an old car?
3) Does this need to go to a mechanic?

Thanks!!!

Should not need to add fluid. Need to determine where it is going. Could be leaking slowly or being consumed if there is a head gasket leak.

Check your reservoir cap. If it's original, it should be replaced.

I'd start with that before I ring the alarm bell.

The coolant expansion tanks tend to crack on the 997.1 after 70k miles - common issue on 997.2?

I'd take it in asap.

Changed the oil a couple of weeks ago. It looked fine.

That sounds like the best possibility!

Members - with a non-pressurize-able coolant system (excluding head/gasket leak/crack), is it likely, or even possible, to boil off this much fluid (through the vapor leak) at the rate he's seen?

No, don't go with the "call it an old car" choices. Cooling systems are closed and have to be to work properly as the pressure in them is one of the things that raises the boiling point of the coolant so the system can work correctly.

Check weep hole on water pump and around the coolant expansion tank for dried white residue. Replace the reservoir cap, as mentioned.

Get a system pressure tested from Amazon and pump it up to about 13 psi and if the needle begins to slowly fall, look for where the coolant is coming out. If the needle doesn't fall, the cap is likely your issue. If after doing this test you get a white cloud on startup, you have a head gasket leak and coolant is making its way into the combustion chamber and being boiled away as steam. If this is happening, one or more of your spark plug tips will be very clean.

Top up with a 50 50 mix of distilled water and pink Porsche coolant from here on out.

@Petza914 I dont know where you store it all :-)

@Carerra keep us posted. Hopefully you find some bubblegum looking stuff around your expansion tank or white residue around your water pump. You need to shine a flashlight on the expansion tank to find any cracks. I regularly looked at my engine bay but you can miss it if you really aren't looking closely. For the water pump get under the driver side of the car near the exhaust and look for any residue on the coolant hoses, water pump, or exhaust. If its on the exhaust or hoses its coming from the tank above. Water pump leaks are usually pretty localized. Coolant has a sweet smell so once the car is up to temp you should be able to smell it in the engine bay.

@Petza914 @TheBruce @Arctic997 @EveryoneElse!

THANKS FOR ALL THE THOUGHTFUL RESPONSES!!

There was a lot of white stuff around the cap, so that sounds hopeful. I will order the new cap, pressure tester, and pink Porsche fluid. I will post an update after I get to inspect as described above and run the pressure test.

Do I need to somehow increase the amount of Porsche fluid since I have added so much DI water? Is a complete flush a good idea or overkill?

That's overkill. There's probably 3-4 gallons of coolant in the total system and you've thrown off the ratio by a few cups - don't worry about it. If you need to top up again, just use straight coolant and worry about restoring the correct ratio at your next water pump change.

The exact 50/50 ratio is not a necessity and our cars have a large coolant capacity. Water boils at 212 and for every psi that the system is pressurized the boiling point goes up 3 degrees. So at 7 psi operating pressure 100% water would boil at 233 degrees - obviously too low. However, water is the best at transferring heat. 100% coolant has a crazy high boiling point but it is a really poor heat exchange medium. That is why the two need to be mixed in order to get both a high enough boiling point and sufficient heat transfer ability. Since you know how much water that you have added (which seems like a lot of water) then just add the same amount of coolant when needed and you should be close. GL

OK, so today, the new cap and pressure tester came. This is the old cap:
https://cimg1.ibsrv.net/gimg/rennlis...075ac4c2e.jpeg
996-106-447-04-M100

I thought for sure that was what was wrong. I put the pressure tester on and it dropped 2 psi in an 1 hour 45 min.

I will get under the car this weekend:(

That cap was definitely leaking. I'm not sure 2 psi in 2 hours is all that bad and sometimes it's very difficult to get a perfect seal with the pressure testers and sometimes their fittings leak a little bit too. I'd just top up the coolant and drive it a bit monitoring the level to see if you're still losing any. If so, then plan on some further diagnostics.

@Petza914 Thanks for the advice!