If you have an aluminum fan Smooth it out for performance.
 

I discovered several issues when dealing with the 450sl.
I have noticed that the radiator fan built up a large amount of heavy scale over the years.
At first I thought that Mercedes Benz and company cast that fan with a very rough surface. I am sure when that car left the factory the fan was smooth.
Heavy scale on an aluminum fan will degrade the performance because of the turbulance delevoped. Smooth that sucker out.

Inspecting: Run your hands on the inside and the outside of the blades of the fan. If it is rough then they need to be polished down. The smoother the better.
It is a mystery why scale builds up in the first place. Time + friction + Static electricity = corrosion is my guess.
Remove the fan and get a couple of sheets of emery cloth. "Sand down" and really polish the rough spots. Pay attention to the inside of the fan blades.

I noticed the same condition on my '73 when rebuilding it. I bead blasted it, painted, then clear coated. Looks are not everything to consider. Having a smooth surface will reduce drag at high speed I would think.

Good post.

If you think about it. Technology on an engine driven fan was limited. there are issues with the Mercedes 107 SL. There is a difference to be noted with the older fans incorporated back in the "day". Now they use a durable plastic fan. Lightweight and scale free.
For People like myself who want to keep "this car of mine as original as possible" I will keep that aluminum fan. I was really tempted to switch over to the electric fan based with a controller and decided against it.
I Don't need to spend the money on a "puller fan" plus the controller.
There are problems associated with keeping the engine cool especially when you are located in temperate areas.
The least amount of turbulance the fan produces the better you will be. Remember that the air is directed over and around the engine as well as cooling the engine itself.

I have polished a few of these fans to the point where they were shiny enough to see yourself in, and they very quickly corroded to a degree. I think that they are made of some different alloy than the valve covers, the alternator, the power steering pump, and so on - those, I've had looking good for years, and the fan's polishing and reflectivity was different no matter what I did.

Maybe it's the exposure to water vapor from rain.

If I do this again, I'll look into clearcoating or powdercoating them with clear. I will say, that powdercoating might add a little weight, and I did worry about the extreme polishing that I did (which was risky, I worried about actually breaking one) upsetting the balance.

I too thought about balance of the blades. That is why I bead blasted, painted and clear coated. Even after blasting the original grind marks and such were still visible so I was confidant that the balance had not been compromised.

If you're looking to reduce the parasitic drag on the engine, you are better off with an electric fan (spend the $) and an automatic thermostat that turns the fan on only at 80*c

It was the scale I noticed that took me a bit off kilter. Now powder coating could be worth a try.
The drag is minimal due to the fan clutch. I just want to squeak a bit more efficiency.

Great subject, I thought that that I was the only person to clean my fans. These are a magnesium / aluminum precision and balanced casting. They get oxidized easily.and need to be cleaned and painted.

Notice the asymmetrical blade spacing and airfoil contours, nice engineering.

Bottom line ...
the sound of the spinning fan and air volume is back to normal.
Don't neglect the fan clutch while you are there.

I tend to agree they need to be painted. Here is one powder coated from a fellow member in another forum. It came out really smooth and nice:)

http://i414.photobucket.com/albums/p...WDERCOATED.jpg

Although I replaced mine with a 16" Kenlowe electric fan as PanzerSD suggests but with a 100C thermoswitch and never looked back:rolleyes:

http://i414.photobucket.com/albums/p...lectricFan.jpg

Deltacom you are very persuasive indeed. I just might switch over because you never know.
In the meantime That is a good picture of a powdercoated fan.

Well Genbilstein, the persuasive aspects of switching to electric fan are manyfold!
As PanzerSD succinctly and adequately described the disadvantages of viscous or fixed belt driven fans as “Parasitic drag” that is the robber baron of HP.

Over cooling of belt driven fans is one of many disadvantages, while on the plus side of electric ones are:, improved economy (it pays for initial disbursement many times over), more performance as it frees up to 4-8% of engine power and up to 8.5% fuel savings, less noise, environment friendly, and other pluses such as less damage to catalytic converters. A look at KENLOWE FANS website is worth it!

Particularly their FAN DESIGN


Alternatively, you might wish to consider a SPAL FAN of similar design.


If you decide to switch to electric fan I suggest a look at this thread concerning the Negatively Closed Thermostat, MB part number: 000589746300 (they are difficult to obtain but you can convert a standard one into a negatively closed one by unhooking the “V” bracket from the top plate). which I had to install when I switched to electric fan and my engine runs cool as a cucumber (80-90C) and the fan seldom comes in unless I am stuck in traffic.

Converting over to a 16" electric pull fan seems to be a smart idea. The caveat would be IMHO converting over to the negative closing thermostat. I understand the principle as to why but the original design was meant to bring the engine up to temp quickly.
Controlling through temperature we all know but how to go about it. I don't care for using a temp probe in the radiator for I believe it is misleading. That placement is competing with the air coming through the radiator itself. You should be able to place a temp probe behind and along the edge of the radiator itself or along the radiator hose.

I appreciate the caveat that would be logical to point out, but the negatively closed thermostat operates just as a standard thermostat in the functioning of the top plate (route to the radiator). It opens and closes as an ordinary thermostat and therefore it does not interfere with duration the engine takes to bring itself to temperature. It retains this functionality on its entirety.

I concur with the placement of the temp probe anywhere, the hose or the radiator itself. It can also utilise the existing auxiliary fan thermoswitch. In some models, mine for example, not having an auxiliary fan originally, the location of the thermoswitch was plugged with a blank bolt which I removed and placed the pertinent thermoswitch for an auxiliary air fan to run the electric fan I installed (see pic red thermoswitch).

In the last 7 years since I installed the electric fan and the negative closing thermostat the only thing to observe is during the winter months the engine runs below 80C and I place a rubber mat 17”X10” between the AC condenser and the coolant radiator from underneath the car resting inside the bottom plastic protector cover (it takes 2 minutes to install/remove) and everything is agreeable.:D

That is pretty cool. I am leaning towards going the 16" fan route and using a controller. I might even go totally unconventional by using an oil temp switch. There is a place for one just below the tensioner. When the oil temp switch opens up then I might have a relay kick in the fan.

I think I would like to have mine powder coated.