Hi, was cleaning the frame on my 87 and noticed a flap (door) on the drivers side in the front. Seems to be spring loaded and quite stiff to move. I imagine it must be for cooling on a when needed basis. I assume then there should be an engine tray enclosing the bottom or what would be the point. Anyway, what makes it open and close? I can't see vacuum line or where one should be, no wires and it seems too stiff of a spring to open from engine heat alone. Any idea?

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1987 300 TDT
1990 300 SEL

Is it on the TDT in your signature and can you post a picture of the vent? Is there a part # on it?

As far as an undercarriage enclosure or "belly pan", I haven't seen a W124 Benz without one from the factory. It may open/close by temp from a bimetallic spring, air pressure, vacuum or a combination of these. Hopefully a member knows for certain.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Yes it opens with heat there is a rather small thermal actuator which moves it.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

OK, I figured heat activated as mentioned no vacuum or electrical connections. The pan is missing from mine, I have a parts car that may have it.

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1987 300 TDT
1990 300 SEL