I bet most 914s don’t have these flaps anymore. These hinged flaps in the diagram are called ‘engine fan flaps’ or ‘non-return flaps’ in the parts manual. They close off the supply air duct path from the engine fan to the heat exchangers when the engine is off by gravity. They open up with the force of supply air to the heat exchangers when the engine is spinning, to circulate air through the HEs into the cabin, as assisted by the electric blower fan in the engine bay.

So the only thing I can figure is that after the car is hot and the engine is shut off, the flaps close to prevent hot air from entering the supply air fan plenum…but I can’t figure out why that’s important.

Any ideas?

they're real flimsy tin pieces....mine actually fell off at one point in time when my heating system was not connected.

b

I believe the purpose of those flaps is so that when the heater blower is on, and the engine is at idle, the heater blower can overpower the main cooling fan and blow hot air backward from the heat exchangers into the main fan area - resulting in warmer air being used to cool the motor.

With the flaps, under this condition, the flaps will close not allowing this backward flow of air. When the engine speed is raised so that there is more pressure from the engine fan than from the heater blower, the flaps open.

Demick

Yup Demick nailed it!

$25 each these days from AA.

QUOTE (North Bay 914 @ Dec 15 2005, 03:13 PM)

I added the double blower to my car, with aircraft quality hoses (from Aircraft Spruce), top and underneath, the little doors are still in place, as are the correct gaskets for the elbows...stainless exchangers. The heat in my car is crazy. Its like sitting next to a fireplace...actually burning your shoes. Defrost works great, even in the rain. Even clears up a stuffy nose. Its like desert heat. ZERO humidity!

And the assumption is your HEs are not swiss cheese either.

QUOTE (Bleyseng @ Dec 15 2005, 03:00 PM)

Yup Demick nailed it!

Nice description Demick.

i'll just make some from aluminum sheet metal.

b

Actually... its all a gag being played on everyone who owns a Type IV powered car.

Like the round holes with the plugs in the body, they are there to make you ask

QUOTE (ClayPerrine @ Dec 15 2005, 04:21 PM)

Like the round holes with the plugs in the body, they are there to make you ask

I thought those were for primer paint flow, ie dipping the chassis at the factory, but that's just a guess.

the flaps also work opposite of each other...the flap over the oil cooler is open when the engine is cold , while the other flap on the other side is closed...as the engine warms up, the thermostat expands opening the flap on the side with the number 1 cylinder, while closing the flap over the oil cooler, allowing the air to flow through the cooler.
Joe

I swear those are aluminum with a foam rubber gasket glued to it (them).

I'll sell some for $24.95 each..........

QUOTE (Demick @ Dec 15 2005, 01:01 PM)

I believe the purpose of those flaps is so that when the heater blower is on, and the engine is at idle, the heater blower can overpower the main cooling fan and blow hot air backward from the heat exchangers into the main fan area - resulting in warmer air being used to cool the motor. With the flaps, under this condition, the flaps will close not allowing this backward flow of air. When the engine speed is raised so that there is more pressure from the engine fan than from the heater blower, the flaps open. Demick

Although I am sure you are correct, I find it hard to believe that the wimpy heater blower has enough power to overpower the flow of the cooling fan, even at idle.

When I took the heater tubes off one of the flaps was missing and one was sitting in the tube off its hinge. I was considering just leaving them out but now maybe I'll clean the one up and fabricate another and put them back in.

-Jeff

I dont think the heat has anything to do with the operation, or engineering of the flaps...when the engine is cold, the flap above the oil cooler is open, allowing the air to pass over the oil cooler, thus the warm oil is being circulated through the cooler allowing the engine to warm up more quickly...after the engine heats up, the thermostat expands, closing the flap over the oil cooler, redirecting the air to go through the cooler to aid in cooling the oil...I inspected mine when I dropped the engine for a tune up, and seals. There has been a thread on this in the past, Brad Roberts also explained it very well...either way, I think it is a good idea for the system to work, and so did the German engineers that came up with it...good luck, Happy Holidays
Joe

Finally bingo Joeav8tor. They are hooked by cable and pully to a Tstat that works simular to a tstat of a water cooled car. They preheat motor then regulate temp thats all.

I live in fla and removed the whole assy and even the heater. Mine was not working cable off pully and jammed shut over heating motor.

Joe/DJ...

We are talking about the lower flaps...not the upper flaps. See the diagram in the first post...

The upper cooling flaps should jam open if the cable breaks or the thermostat fails so there is no way it will overheat the engine.

last time i was under there i noticed the starboard side flap was missing. since the system had never been taken apart prior to my tinkering, i can only assume that flap is still hangin around in there somewhere.

~a

sorry about that, I saw the beginning diagram, I still have the flaps on my 2.0 which are free to open and close by forced air....Joe

Those little post-fan, gravity close, tin flaps right? I asked the same thing at my first engine pull party. Being a newbie, I either got the correct answer from a couple guys “in the know” or, everyone had a good laugh when I left.
* (see Snipe Hunting)

The reason for the flap is to keep mice from getting into the engine compartment. Supposedly the VW/Porsche engineers could foresee mice nesting in the fan housing. I guess it’s a bigger consideration when a car is sold globally.
A couple of the guys said they weren’t really needed and took theirs off. If they stick, it could hinder flow. But if a mouse does get in, it could smell really bad when you start up the engine.
Hummm.