996 C2 DIY – AOS replacement, Y-cable and hot starting issue fixed

996 Carrera 2 – AOS and Y-cable replacement, smoke test and hot start problem solved​ Hi everyone, I'm a Porsche 996 Carrera 2 Cabriolet owner from the Netherlands. My car is a 2000 model with approximately 144,000 km (89,500 miles). Recently, I carried out some maintenance on the engine and wanted to share my experience, especially since this was my first time doing this kind of work on my 996. Why I started this project For some time, I had been experiencing difficulties starting the engine when it was hot. Cold starts were generally fine, but restarting after a drive was sometimes a problem. I also noticed some oil seepage around the Air/Oil Separator (AOS). Since I was already planning some maintenance, I decided to replace it preventively. While I was at it, I also decided to replace the Y-cable and the serpentine belt. Getting access to the AOS To reach the AOS, I lowered the engine slightly to create enough clearance to remove the coolant expansion tank. This allowed me to remove the intake manifold and gain access to the AOS. I have to admit, this took me quite a bit of time! But since it was my first time doing this job, I was taking my time and figuring things out as I went along. Once I had access, I removed the old AOS. Interestingly, the old AOS itself showed no visible signs of failure or damage. However, I noticed something unusual. The lower corrugated rubber hose was secured with an adjustable worm-drive hose clamp instead of the original Porsche-style clamp. I suspect this may have been the actual source of the oil seepage, rather than a failure of the AOS itself. In hindsight, the AOS might not have needed replacing, but since I had already gone through the effort of accessing it, I decided to install a new original Porsche AOS anyway. I also replaced: The Y-cable (starter/alternator cable). The serpentine belt as preventive maintenance. A damaged vacuum line. Checked and refitted the intake connections. An unexpected problem – the smoke test saved me! Unfortunately, after reassembling everything, the engine wasn't running properly. It turned out that one of the AOS hoses had come loose during the work, but I hadn't noticed it. After checking several things, I decided to perform a smoke test on the intake system using a smoke leak detector. That's when I finally discovered the disconnected AOS hose! Once I properly reconnected the hose and checked the intake connections, the engine ran smoothly again. A valuable lesson learned: always double-check those AOS hose connections. A smoke tester can be a real lifesaver! Refilling and bleeding the cooling system After completing the repairs, I refilled the cooling system. Following advice from a Porsche specialist, I raised the rear of the car so that the coolant expansion tank became the highest point of the cooling system. The idea was to help trapped air escape more easily and speed up the bleeding process. I left the bleed valve open during the initial bleeding process and monitored the coolant level and engine temperature. After the first few drives, I only needed to top up the coolant slightly. The level is now correct. The results The engine now starts immediately, even when fully warmed up! The idle is smoother, and the engine seems to run better overall. I strongly suspect that the old Y-cable was responsible for the hot starting problem. As for the AOS, I now believe the oil seepage may have been caused by the non-original adjustable hose clamp on the lower corrugated rubber connection rather than the AOS itself. All replacement parts were original Porsche parts, costing approximately €360 in total. I carried out the work myself. Although the job took quite a few hours, mainly because it was my first attempt, it was a very satisfying project. Lessons learned: Lowering the engine slightly provides the clearance needed to remove the coolant expansion tank and access the AOS. Take your time when removing and refitting the intake manifold. Check the condition and type of hose clamps around the AOS before assuming the separator itself is leaking. Double-check all AOS hose connections before reassembly. A smoke test is an excellent way to find hidden intake leaks. If your 996 has hot starting problems, checking the Y-cable is definitely worthwhile. Raising the rear of the car can help with bleeding the cooling system. I'm very pleased with the result, especially considering the relatively low cost and the experience gained from doing the work myself. Two questions for fellow 996 owners: Has anyone experienced oil seepage around the lower AOS hose due to an incorrect or non-original hose clamp? Has anyone else solved hot starting problems by replacing the Y-cable? I'd be interested to hear your experiences. Greetings from the Netherlands!