Not sure if I'm posting this in the correct forum, or if maybe this is a second gen 126 thing and the 300SDLs have it... it being a mystery to us, thus i've come here. My friend Turbobenz pulled this out of a 420SEL. He found it wrapped in insulation in line with the compressor low side. He said it was full of fuel in the jacket. What is this doing to the fuel? or is the question what is this doing to the freon? Anyone know? has anyone seen this? It looks awesome polished!

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Fuel cooler.

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Satan creates nothing: he only ruins everything. He does not invent: he tampers. And his followers are no different ~ Archbishop Carlo Maria Viganò

My 560 SEL has one also. It confused me at first sight also.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Why would the fuel need to be chilled? But only with AC? Or does this ad heat into the low side of the AC system to expand the gasses?

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1981 300SD 512k OM603

With the AC running, this line is chilled. Without, it still acts as a huge heat sink. But I am not sure how effective it really is on a return style system where fuel flows at a pretty good rate.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

I scratched my head when I saw mine. Maybe it was designed to control vapor locking during hot summer AC use. Dunno.

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Satan creates nothing: he only ruins everything. He does not invent: he tampers. And his followers are no different ~ Archbishop Carlo Maria Viganò

That's my guess as well

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

Why would adding heat to the low side prevent vapor locking in the AC? What is vapor locking? When it can't Compress the gas into a liquid on the high side?

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1981 300SD 512k OM603

You're looking through the wrong end of the telescope. The exchanger is removing the heat from the fuel not adding it to the freon. Well, actually it IS adding heat to the freon but the cooling system is designed to dissipate the heat whereas the fuel system is not.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

It has the appearance of something used for distilling spirits.

Maybe you found another use for the Benz!

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Sam

84 300SD 350K+ miles ( Blue Belle )

cool fuel is higher density, more power. hot fuel is lower density, perhaps it vaporizes too easily...
gassers... sheesh!

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My drivers:
1987 190D 2.5Turbo
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1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Not only is it a heat sink to cool the fuel on the return side but I imagine it also acts as a baffle to smooth out surges in the fuel supply.

The CIS system is a fairly primitive set-up. Effective yes but not exactly technologically advanced. 'Course, "if it ain't broke, don't fix it" is a pretty safe way to ensure reliability.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now