Can someone please explain what the MB engineers were thinking when they designed this? It's an air horn that feeds into the battery tray. The air horn is attached under the headlight and feeds cool air, and rain water, to the bottom of the battery tray. I can't figure out why they would design this. Does the battery get hot? I checked the EPC pictures and, sure enough, the parts are correct. It's called an "air horn." Pic1 shows the air horn feeding into the tray. Pic2 shows the hole at the bottom of the tray where the air horn attaches.

The bottom of the tray was rusty, but not too bad. I refinished with Por15 and Underhood Black. When I reinstalled the tray I decided to leave out this fancy air horn.

Attached Thumbnails

   

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2009 R350, now the daily driver
1980 300SD, was the daily driver

When it's being charged it does. Some vehicles have a battery temp sensor to prevent excessive battery temps.

SomeBody, realized they had a OverTemp Battery Charging problem...
[Spelled and Pronounced "Battery Location in the Chassis"]

What you're seeing is a Mercedes "Hack" to try and Alleviate (NOT FIX) the
problem!

[Heat is your Battery's worst enemy!]

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'84 300SD sold
124.128

If it was in the EPC, it's not someone's hack.

Got a part number for that?

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

He's calling it a hack by the engineers.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

BMW puts batteries in the trunk for that very reason.

My Volvo S80's battery was in the trunk too.

BMW probably says it's for weight balancing or some-such

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

No. They say it's to avoid the heat of the engine compartment, which is particularly important considering that they are using AGM batteries.

Perhaps this is another reason for a double firewall also

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

This sounds like a valuable device. Having battled a vehicle a decade ago that had the battery placed in a "hot spot" in the engine compartment with no air flow this would have come in very useful. That vehicle would eat a battery in two years.