Howdy to all,
I was just investigating (and fixing) a Coolant leak under the front end, when I came across a hinged flap/door which is located in the Fan Shroud towards the bottom of the R/H Thermo Fan. Its probably 1-1/2" x 4", its hinged at the top and gravity keeps it closed. The hinge action is very loose, so the first thing that went through my mind was; I bet this is the source of the pesky rattle that I've never been able to pin point. (until now)

My query is: what does this flap/door do and how is it actuated ?

When open, all you can see is just the inside fins of the Radiator.

I was not under the car while the Thermo Fans were ON - maybe they blow the flap open ?? (I don't think just forward momentum of the car would do it)

Any thought and suggestions - highly appreciated.

 

It sounds like a bypass area that if the fan shroud gets blocked by something, this will atleast give you a little bit of cooling. I would need to crawl under my car to see if my car has one just to make sure.

 

The 3 plastic doors in the fan shroud are:
+ Blown open at highway speeds, to increase the surface area of air flowing thru the radiator.
+ Sucked closed by the fans when the car is stopped or moving slowly, so the fans suck more air thru the radiator.

If the plastic doors were removed or missing, the fans and radiator would be less effective when the car is moving slowly, because the fans would suck more air thru the openings, and less air thru the radiator.