991 Coolant Leak - DIY

[Traveller]

2015 Porsche 911 Carrera 4 GTS. Purchased from the original owner in 2018 (3y 1m after initial delivery) with 98 miles. Coolant pipe started to leak intermittently in May 2020. It was an intermittent and a slow leak. I never had to add any coolant to the coolant reservoir. Then during my first two drives in 2021, the coolant pipe leaked each time. Although I am still under CPO warranty and if anything I trust my local dealer far more than the independents, I chose to fix this myself.

I found plenty of coolant leak complaints on various forums, but it seems 991 owners had them fixed under warranty. I did come across a Rennlister in the UK who clarified some of the questions I had.


The typical coolant leak in the 991.1 and 991.2 models. Some owners have had issues with leaking coolant pumps. Luckily I haven't...yet.



I didn’t want to drain the whole coolant system, so I parked my 991 in my sloped driveway with the nose down. By the time I set both back wheels on car ramps, the engine was far above the rest of the coolant system. I drained 8.5 liters of factory coolant. Upon filling, it took just over 8 liters and will get topped up after the next few short drives. I have a vacuum filler, but it was not necessary or used. I used a 1000 ml graduated cylinder and marked off each liter with an automatic punch and later filled in each punch hole with a permanent marker.



Text within brackets eg. (#25) refer to the parts in this diagram.



I removed the E10 Torx bolt - M6 x 12 (#30) that fastens the silver coolant pipe (#25) to the engine block. After removal of that fastener, that pipe can now be pulled out of the thermostat housing (#19).



I removed the E10 Torx bolt - M6 x 12 (#30) that fastens the black coolant pipe (#26) to the cover of the high pressure pump. Without removing that bolt, you won’t be able to remove the black coolant pipe from the thermostat housing (#19).



I removed the E10 Torx bolt – M6 x 16 (#29) that fastens the black coolant pipe (1) to the thermostat housing (#19). That black coolant pipe can now be removed from the thermostat housing.

Coolant pipe 1 is #26 in the Coolant Parts Diagram.
Coolant pipe 2 is #25 in the Coolant Parts Diagram.
Coolant pipe 3 is not shown in the Coolant Parts Diagram.



Shown is the coolant pipe retainer after the E10 Torx bolt – M6 x 16 (#29) that fastens the black coolant pipe to the thermostat housing (#19) is removed.



I removed the two E10 Torx bolts – M6 x 20 (#9) that fasten the guard plate (#22) in place. Then I removed the electrical connector that the guard plate covered.

[Traveller]

I removed the two E10 Torx bolts that fasten the thermostat housing (#19) to the engine.



I removed the two E10 Torx bolts that fasten the thermostat housing (#19) to the engine. This bolt (removed) attaches the bracket (#32) on the coolant pump to the thermostat housing.



I removed the two E10 Torx bolts that fasten the thermostat housing (#19) to the engine. The thermostat housing can now be moved to the rear allowing access to the O-ring (#12) and mating surface of the plastic coolant pipe (#11).



O-ring (#12) has been removed and the mating surface as well as the groove for the O-ring has been thoroughly cleaned. The plastic coolant pipe (#11) has been updated but in order to replace it, the coolant pump and other parts would have to be removed. This can be done at a later date or when this joint leaks again. The updated part is shown near the end of this photo series.



After a long drive, no more leaks.

Note: although the points where the fasteners are, are flush, there is a 0.019” gap between the plastic coolant pipe and the thermostat housing between the fastener points. It could be why Porsche updated the plastic coolant pipe and added gussets. I’ll get around to installing the updated coolant pipe if I have further issues down the road, but that involves taking off the coolant pump and other parts. At the moment, I want to drive!



Original PN: 9A1 106 238 00
Updated PN: OPB 121 076



Those nubs are there to keep the water pipe seal (#12) in place while it sits in the groove of the water pipe (#11). The issue is the groove is wider than the width of the seal allowing it to squish and flatten more easily. Maybe that is why this joint leaks after a period of time.

Original PN: 9A1 106 215 00
Updated PN: OPB 121 437

[Mark44]

Excellent writeup and pictures!

[Str8Razr]

Wish my engine looked that clean. For future leak seekers, the stock Porsche coolant will glow under UV light. I just checked. Also stock Mercedes coolant glows as well as Liqui Moly Moly Gen. UV flashlight's are cheap and useful.

[Traveller]

Originally Posted by Mark44

Excellent writeup and pictures!

Take the pics gets in the way of doing the actual work, but since this issue is quite common, I decided to write one up for 991 owners that are no longer on warranty and have the skills. If I ever replace the "upgraded" coolant pipe that I bought should replacement of the O-ring seal leak again, I'll do so. That job is a bit more involved.

On Rennlist, members were saying you cannot get to the O-ring seal. You can, if you remove the three metal pipes from the thermostat housing and remove the two E10 fasteners holding the themostat housing in place. At that point the thermostat housing just swings out of the way towards the rear of the vehicle and you can very easily get to the plastic coolant pipe.

[Traveller]

Originally Posted by Str8Razr

Wish my engine looked that clean.

Well it is a toy and not a daily driver. My motorcycles are that clean as well and they have actually been on long tours locally and in Europe. Even my 1990 BMW R100 GS is that clean with aluminum castings that look like the day I bought it new.

Originally Posted by Str8Razr

For future leak seekers, the stock Porsche coolant...

Can be replaced with Zerex G-40 (pink) in case someone was not aware of that. Same stuff that BASF used to make for Porsche before they sold rights to it.