viperbob

The fan assembly uses a flapper valve to open and close for allowing airflow from the fan to the blower motor, down through the heater pods on the exhaust and then through the system to the cabin. The valves under the car open when air is being passed to the cabin, but the HVAC has the vents closed. This allows the flowing air to escape. When you install the RS or CF tube, you will get a constant flow of air from the fan going through the tube, but in most cases you are using this for summer and the cabin vents are closed so the air goes out through the valves under the car. What I did on my car was to install a round piece of aluminum into the plastic outlet on the top of the fan. WHile it fit tight, I still installed a small hole through the plate and the plastic and used a tie wrap to make sure it did not pop out under extreme conditions. The older 3.2/3.0 engines had a blockoff plate available that replaced the entire neck off the fan assembly and forces all the air through the engine. This then does the same thing....

Robin 993DX

Doesn't the heater tube (fan) serve another additional function to take excess heat from the engine to prevent heat soak when the temperature exceeds a preset value?

I always hear my fan run during the summer month to blow excess heat from the engine. So I assum installing this tube would render that cooling function useless.

epj993

Robin, I think you are correct - per my owner's manual.

Flying Finn

Thanks Bob, makes perfect sense. In my 911 (2.7 engine) I blocked the "same" thing and now will do the same.

I've seen photos of the piece you talk about (at least Kim & Princeton has one), no problem to fab up something like that.

Thanks!