Hello Rennlist! I have a 2012 Cayenne Turbo with about 127,000 miles on it and recently I noted a slight coolant smell after driving, but there were no obvious signs such as leaks on the ground, wet areas around the radiator, coolant tank, or hoses. I also noted that my coolant level was dropping a little at a time, but certainly not drastically.

Like many of you who read posts here and on other sites, I made the assumption that it must be one of my glued in fittings that were coming loose on the thermostat housing, or perhaps the thermostat housing itself or the seals were leaking and the coolant was ending up in the "V" of the engine, which is why I didn't see any obvious signs.

I removed the intake manifold to verify my suspicions, and sure enough, coolant was in the "V" of the engine down under the fuel rail, wire harnesses, and and starter. The interesting thing, however, was that my thermostat housing and the glued in pipes were actually fine and quite strongly fitted ... no leaks from the glue, no leaks from the housing itself, and no leaks from the thermostat insert o-rings either. After further examination, I discovered that there is a plastic "Y" hose that connects to each head on either side of the thermostat housing. This pipe is the coolant vent line, which connects at the back of the engine to a hose. Here is the diagram of this line:


What I noted is that one of the points that connects to the passenger side head had broken nearly off the pipe (it ended up fully breaking on removal) and the other one had broken on the insert where the o-ring is. Both sides being compromised allowed coolant to escape into the "V" of the engine and is why my particular leak was a very slow one. Here are some photos of the actual part and the broken pieces. The first two photos show what cracked/broke, the third shows how it looks right after taking the intake off, and the last photo shows where the pipe is after removing the fuel rail.






Fixing this is actually very easy as the one end connects to a hose with a spring clamp, while the two ends connect to the head with a single torx bolt. The part number for this part is 948-106-026-22 and its about $50. Since I'm already "in there", I've decided to go ahead and replace the thermostat housing with the upgraded Porsche housing that bolts the pipes in (rather than glue) Part # 948-106-080-02 (why take chances) and install a new thermostat unit/seals, Part #948-106-034-01, new water pump, and gasket, and o-rings on the two pipes that attach into the thermostat housing and where the housing mates up to the heads. Based on my experience, I highly recommend you also replace the plastic coolant vent line If you decide to tackle this job as it is likely it is getting brittle with age and can break, causing a small leak that is annoying at best.

I hope this helps someone out on Rennlist and gives something new to consider. Its interesting that the much discussed glued in pipes on my car, at least, were still quite strong and showed no signs of failure despite the amount of miles on my car.

By the way, the thermostat housing, thermostat and water pump on my car was original ... lasted 127,000 miles and showed no signs of failing, but I took the opportunity to replace anyway.

 

Also see: https://rennlist.com/forums/cayenne-...-firewall.html - for info on how to gain more room to work on the rear of the engine. GREAT posting!