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Mercedes Electric Fan Install


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All parts used in these pictorials are available at the diesel parts for sale page


Mercedes Electric Fan Install

One of the best way to grenade your engine is to let it overheat.  Heat kills!  Since most of these fine machines we love to ride around in, are approaching the 1/4 century mark, they are due for some serious maintenance.  Mercedes in their infinite wisdom some years ago decided to use the viscous fan clutch set-up on their diesel cars.  In an effort to save fuel with less fan drag, reduce noise and control the cooling fan when not needed, they went to the fan clutch system.  I cannot say this is the best way to cool the engine down in the 21st century.  In my experience, most of these cars are still running around with the ORIGINAL fan clutch, and its NOT WORKING.  This can be a major source of overheating your engine in stop and go traffic. 

Remember that over approximately 25mph, the amount of air that comes through the radiator just from the movement of the car, is far more than any fan could produce.  So the fan is only effective below that speed.  If your car is over heating at faster speeds, then you may have other issues.  Overheating can also be caused by many other factors: stuck thermostat, clogged radiator, worn water pump, clogged cooling passages in the engine, etc.  So the fan is one part in the total cooling system package. 

Keep in mind that I am of the mindset with these fine cars, to keep them stock.  However, there are some issues that just can't be addressed properly in the stock configuration.  So I decided to do the unimaginable, install an electric fan on my '81 300d.  I decided that in the end it had to look like its been there for 20 years.  It had to fit, function and operate on its own and keep the car cool.  Below is the fruit of my efforts.  I am extremely happy with how the project turned out and by george, it looks like it should have been there from he factory in '81.

So follow along as I install the dieselgiant.com 123 electric fan kit.

Safety and security tips:

Please remember to recycle all your used fluids at an appropriate recycling center.  Be mindful to not spill or splash fluids on yourself, others or the ground.  Also as a safety tip please remember anytime you are working on, around or under your car, to wear safety glasses and secure the car with wheel stops and approved jack stands! 



Here is the stock fan and shroud.  Turbo and non turbo models will be similar.



With a 10mm wrench remove the four retaining bolts that hold the fan and clutch assembly to the belt pulley.


Remove the fan and put one bolt back into the pulley so it does not fall off.


Use the supplied retaining lock rings, one for each bolt.


Tighten all the bolts and retaining lock rings to the belt pulley.


Now remove the pressure clips that hold the fan shroud to the radiator.


Remove the shroud and this is what is left.  Lots of space!


This is what you will be installing.  The dieselgiant.com electric fan retrofit kit.  Almost 2000 cfm of air flow.


Old shroud vs. the new electric fan assembly.




This is the side that will go against the radiator.


The fan is thermostat controlled and the sensing bulb at the top is part of that circuit.


Simply turn the fan sideways so the control box is facing the passenger side of the car.  This will allow the

fan to fit perfectly between the ridges of the radiator tanks.



Using the supplied fan bolts and press nuts,  This is the orientation of the hardware.


This section will slide though the fan mounting holes and then through both the radiator and condensor fins.


Plastic bolt is gently pushed through the fins


The shock isolator and push nut slide on the bolt.  Just use wire cutters to trim the excess bolt.


All attaching bolts and push nuts have the fan secure to the radiator.  Push against the fan shroud to compress

the soft gasket so the push nuts are very tight.   This ensures the fan shroud gasket is sealed on all sides of the



Now remove the fuse block cover to gain access to the power we will need.


You will need a circuit that has power in the start and run mode only.  This ensures the fan will NOT

run unless the car ignition is on.


Using the supplies wire and connector, install it on the end of the wire and bend over to a 90 degree



Circuit 4 on this model is what I chose to use.   It is the cigar lighter and glove box circuit.


Models years may differ.  Just look on the inside of the fuse cover plate to see which circuit to use.



Now run the power to the internal relay  and the other terminal is the ground.  The instruction sheet

in the kit will show you which terminal to use.


I used the car battery ground connection for my ground.


The supplied inline fuse is where we tap our battery voltage for the main fan motor.


I hooked one end to the positive battery terminal and the other end......


....I just used a butt connnector to the wire that runs to the control box.  Remember the 12 volt source

from the fuse block only powers the fan relay, the 12 volts from the battery powers the fan itself.


The route the wire in the factory harness bundle  if you like a clean install.

All the way to the fan.


The last 12 inches or so use the supplied wire loom protector.  Gives it an organized look.

You can hook up the fan to run when the ac compressor cuts in, but the factory aux. fan does that job fine.

The temp will go up quickly and turn our electric fan on anyway, to I chose to not hook up that circuit.


This is what you are supposed to be reading if all is well.  If its 100 plus with the ac on, yes it will

go higher but you will have the confidence to know that in the area of air flow, you have done all

you need to do.


No go out and enjoy your ride!