Cable to airway flapper broken

[tmeracz]

Now that I'm getting some quality time with my naked Type4, I've noticed that the cable leading to the flappers on the fan airways is broken.

Just a guess, but I'm thinking this would contribute to my lack of stable idle when cold? (I've always had to keep my foot on the gas until the engine gets to normal operating temps)

I'm looking at the design, it looks like the flap over the oil cooler is closed when the flap on the opposite side is open and vice versa when the flap over the oil cooler is open. I don't understand the reasoning behind this, other than to expose the oil cooler to as much ambient hot air as possible until the engine warms up, at which time the flaps on the airways would adjust to blow cool air over the oil cooler.

Is this the correct position for these flaps or is the offset the "genius" of some previous mechanic?

Anyone onlist care to straighten me out on this?

[Dave at Pelican Parts]

The flaps are working as designed. However, your understanding of what they are actually doing is imperfect.

Having the right-side flap "closed" actually creates a nice little duct for air coming off the fan to be pushed through the cooler. If you look closely (assuming you have an engine available to you with the flaps in but the engine in off), you can see that the leading edge of the "closed" flap is up somewhat from the edge of the fan shroud. This means that a portion of the air going to that side of the engine is being diverted and pushed down through the oil cooler.

Similarly, when the flap is "open", the edge of the flap moves downward, blocking this path for the cooling air.

In other words, don't freak out--it's perfectly normal.

--DD

[tmeracz]

OK, that makes some sense. But why design the system with an opposing flap on the other side? Wouldn't it be optimal to cool the block regardless of the flap position over the oil cooler?

[Tidybuoy]

I believe one of the reasons for the flap design is to divert air from the engine when it is warming up - similar to how a thermostat on a watercooled engine prevents water from passing thru the block when warming up.

Vern