996 Carrera etc, the fan on the underside of the engine lid

[monthefish]

996 Carrera etc, the fan on the underside of the engine lid


located just underneath this vent,


does it:

(a) pull ambient air down into the engine compartment (fighting the hot air inside's tendency to rise)
or
(b) draw the air from out of the engine compartment upwards so it can escape through the vents in the engine lid.

Neither situation seems optimal.

If it's (a), where is the hot air from the engine designed to vent to?
If it's (b), is that not putting hot air right into the path of the engine/airbox air intake?

[PTT]

Is that fan not only running when the engine is turned off and then pushing hot air out
through the engine lid.

[Polome]

can't remember if fans sucks or blows...its switched on ,engine running or not when engine bay high temp detected. E.g. In traffic jams ..stationary after a fast run etc...hope this helps.

[r.g.]

Pretty sure it sucks.

[IknowJoseph]

I never noticed mine coming on - apparently it vents hot air out when the engine bay gets to a certain temperature, but I've never seen it.

[monthefish]

r.g. said:

Pretty sure it sucks.

up or down?!?

[IBM9000]

On the carrera it sucks air in. It only comes one when the temp sensor (right hand side of the engine as you stand from the rear and look at the car)detects that the engine compartment is very hot.

In the uk it rarely comes on but in this current heat it probably would. It runs after ignition off.

On the 996 turbo it is on all of the time when the engine is running. Sucking air in.

If it's (a), where is the hot air from the engine designed to vent to?
The bottom of the car, though it does seem to be an inefficient way to do it.

If it's (b), is that not putting hot air right into the path of the engine/airbox air intake?
The airbox intake has a seal around it underneath the lid so the air drawn in doesn't affect the air intake for the engine.

Edited by IBM9000 on Wednesday 20th July 21:56

[Rockster]

monthefish said:

996 Carrera etc, the fan on the underside of the engine lid


located just underneath this vent,


does it:

(a) pull ambient air down into the engine compartment (fighting the hot air inside's tendency to rise)
or
(b) draw the air from out of the engine compartment upwards so it can escape through the vents in the engine lid.

Neither situation seems optimal.

If it's (a), where is the hot air from the engine designed to vent to?
If it's (b), is that not putting hot air right into the path of the engine/airbox air intake?

Probably repeating what others have offered...

While there is of course a tendency for the hot air to rise the fan can more than compensate for this.

So the fan blows down.

The idea is to blow the hot air out from the engine compartment and out from under the rear of the car. The hottest air is around the exhaust system and the goal is to avoid letting this hot air rise inside the engine compartment and "cook" the wiring harness, hoses, fittings, etc.

The Turbo engine compartment fan can be fused -- there is a separate fuse for this -- to run all the time the engine is on. Mine is fused that way.

The Turbo engine of course has those very big -- relatively speaking -- and very hot turbos so the idea is to continuously blow cooler air down to prevent the extra heat produced by the turbos from cooking the hardware in the engine compartment.

Price a new engine wiring harness and you'll appreciate the engine compartment fan.

At speed engine compartment cooling is helped by the build up of air pressure over the engine compartment deck lid helped in part by the spoiler that rises at speed.

A hard working engine produces a lot of heat and not all of it is shed via the cooling system. The hot exhausts which can be a dull red from heat when the engine is working really hard emit copious amounts of heat.

Be aware the fan can come on at any time after the engine has been shut off (and if the engine was hot when shut off) so don't inadvertently (or advertently) stick your fingers in the fan blade enclosure.