On one really hot day last summer...

[abhirud07]

Last summer (I know I am just a tad late) my car (5000cst) stalled at a traffic light. I cranked and cranked but she just wouldn't turn over. I waited for about 10 minutes, while angry drivers passed by, and cranked. This time she fired up. I had to hold the gas pedal down slightly while the light turned green (in neutral) and then shifted into drive because the car kept stalling. I pulled over further down into a parking lot and the car stalled again. This time I waited for nearly 2 hours before going home. At first I had thought that the engine definatley must have overheated, however I had suspicion because the warning light had not come on, and the temperature gauge was on the center line (it was one of the hottest days during summer, central NJ). I thought that my thermoswitch was blown because I don't believe I heard the fan come on at the light. Also, about a week before this calamity I had mounted on the fuel injector shroud cover (which was previously removed) because it was broken and I had to fix it. How do you tell that the shroud cooling fan/pump is working, and when it should come on? I noticed when I put on the fuel injector shroud cover, it completely covers the fuel injectors and leaves no room for air to come in. At least before when the cover was not mounted the fuel injectors were exposed to air. Could this be a problem too? That my shroud cooling pump isn't working, and that it's the fuel injectors that are just getting overheated? Oh yeah, and in the winter the car is amazing!

[RussB]

Sounds like vapor lock, which the injector cooling fan will help eliminate (if it's operational).

The thermoswitch for this cooling fan has a single wire and is mounted atop the wastegate heat shield.

Test it with a heat gun.

If the fan never turns on, either the thermoswitch, its relay, its fuse, or the fan (or all four) is kaput.

*IF* the injector cooling fan operates and you still experience vapor lock, residual fuel pressure may be low; perhaps the fuel check valve is intermittently failing (which they will do).

BTW, the rubber shroud, according to Bosch / Audi, covers the fuel lines to the injectors to both reduce heat soak when off and fire retardation: it prevents fuel from spraying directly on hot engine in case of a fuel line break/leak (God forbid).

[qpower]

VACUUM LEAK?

[jurq]

and the injector cooling fan should come on as part of the after-run cooling program. If if does not, then the fan or the fuse is gone. If it comes on, but not during after-run, then the relay is shot. The shroud directs air directly onto the injectors to reduce the liklihood of vapor lock. I would agree with qpower that this sounds somewhat like a vacuum leak, particularly somewhere between the turbo and the intake manifold.

[abhirud07]

Ok, so I know that on that day it was vapor lock that stalled my car. But I also think my thermoswitch for the radiator/after run fan might be blown too. While recently driving the car, I noted that at traffic lights or in stop-and-go traffic it's not coming on. I heard that replacing this thermositch is risky because the threads on the radiator are made of plasic, which becomes brittle and can break when removing the switch. Is this true? I currently have a new thermoswitch for the radiator/afte run fan, but can't decide on what to do.

[RussB]

Use a 29 mm deep socket for the radiator fan thermoswitch (on the rear surface of the radiator, just beneath the lower hose). You'll need to remove the lower radiator hose to access it, which means that you'll lose a lot of coolant, so have some fresh coolant ready to refill.

BTW, though the cause of the radiator fan not runnnig when it should may be a defective thermoswitch, a failed relay will also cause the same problem.

The after-run thermoswitch for the radiator fan (and coolant pump) is located on the rear surface of the aluminum casting that joins the upper radiator hose to the cylinder head. It has two terminals.

[Sergei]