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1982 Mercedes 300TD wagon
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1,048 Posts
Discussion Starter #1
Like most older cars, mine likes to run on the hot side while running with the a/c on. The aux cooling fan works but it always seems to turn on too late. I'd like to either wire it so I can turn it on with a toggle switch or see if there is a larger electric fan I can run (if it fits).
How difficult or feasible is this idea?
 

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1985 300D W123 Cali
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1,408 Posts
some have run W126 fans. you have to remove one of the diagonal support bars that the W123 fan attaches to. perhaps there are other cooling issues that need to be addressed.
 

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W-1-2-3 Go!
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16,161 Posts
A larger fan as mentioned has been a common modification. A lower-rated temperature switch may allow the fans to initiate earlier. Asgeir did a modification for my 190E so the fans turn on a little sooner.
 

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1982 Mercedes 300TD wagon
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1,048 Posts
Discussion Starter #4
I need to talk to that guy before my trip. I need a new starter and if he could modify the fan that would be awesome
 

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300SD
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11,191 Posts
Can someone post a few close up pictures of their original auxiliary fan as it is mounted? I am replacing mine and do not remember if the 5 mm bolts are threaded into the fan housing or from the other side and secured with nuts to the diagonal brace clips. Also, a photo showing routing of the wire harness would be of interest. (Note: I had the old fan removed from the car over a year).

Thanks.
 

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I'm planning to add a manual toggle switch as well. What I have found is that on two different W123s, I had replaced the entire cooling system with OEM parts, they still ran at 100 degrees climbing elevation and would take a long time to cool down, so even with a new OEM system, the fan should be on in summer weather when driving in mountain areas.

I remember seeing an old thread here from MBeige talking about a group buy to get some type of climate sensor that would turn on the fan automatically at around 90 deg C. I looked into this myself and it seems like it would require a decent amount of engineering. Has anyone done this type of setup on a W123?

Dkr.
 

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1981 300d
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Like most older cars, mine likes to run on the hot side while running with the a/c on. The aux cooling fan works but it always seems to turn on too late. I'd like to either wire it so I can turn it on with a toggle switch or see if there is a larger electric fan I can run (if it fits).
How difficult or feasible is this idea?
Back to basics is the theme - a bigger fan is a band-aide fix and may be missing the true issue, older cars have contamination in hoses, block and radiator, start by looking for kinks on firewall to LHS lower block, remove a few hoses and look for sludge in system - a good signs the rad is also restricted.

Sometimes cheap jobber thermostats and temp switches don't meet OEM specs and cause problems, lose fan belts on generator / crank / water pump are also culprits

Go back and cover basics to this simple design and......KISS
 

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1981 300d
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21 Posts
Keep it simple

Like most older cars, mine likes to run on the hot side while running with the a/c on. The aux cooling fan works but it always seems to turn on too late. I'd like to either wire it so I can turn it on with a toggle switch or see if there is a larger electric fan I can run (if it fits).
How difficult or feasible is this idea?
Back to basics is the theme - a bigger fan is a band-aide fix and may be missing the true issue, older cars have contamination in hoses, block and radiator, start by looking for kinks on firewall to LHS lower block, remove a few hoses and look for sludge in system - a good signs the rad is also restricted.

Sometimes cheap jobber thermostats and temp switches don't meet OEM specs and cause problems, lose fan belts on generator / crank / water pump are also culprits

Go back and cover basics to this simple design and......KISS
 

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1972 280 SEL 4.5 (sold) 1971 280 114 Coupe (sold) 1988 300 SE 2005 jag XK8
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2,218 Posts
100 degrees C is not hot let alone warm! Running a fan at 90 degrees reduces engine efficiency and is a waste of electricity. You guys have to realize the hotter you run an engine and keep the temp stable is always better than too cool. If it runs above the temp rating of the thermostat most of the time, you have other issues, restricted radiator, weak pressure cap, loose belts, weak fan clutch. The cap and fan clutch are the most overlooked things on this car.
 
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