Mike Frank wrote this info up, it's also found
in the Diesel-Benz digests on this server:

I manufacture electric fans, but not for Mercedes applications. In general, an electric fan will be more efficient than an engine driven fan, since the electric fan will run only when needed. A mechanical fan always places some drag on the engine, even if it has a viscous coupling.  As for sizing, a 3L Diesel engine would probably do quite well with a 1500 CFM fan.

You have a few things to consider:

- You need to either use a shroud or else use a fan with a slinger ring design.  Most aftermarket fans are self contained, with one or the other of those designs.

- You need to get the shroud  (or slinger ring) as close to the radiator core as possible. Most aftermarket fans come with plastic rivets that hold the assembly to the radiator core. This is an abominable design. Spend some time with the fan and figure out how to build a proper support.

- You will need to find a way to control the fan. There are any number of aftermarket switches that will work beautifully, and won't require tapping the block.The slickest is made by Permacool. It senses the temperature of the core, and manages the speed of the fan to provide the best compromise of cooling and noise.

- Given a choice between a small diameter fan and a large diameter fan, both of which pull the same amount of air, go for the largest fan that doesn't exceed the size of your radiator.

- Aftermarket fans can draw anywhere from 6 amps to 60 amps. Current draw has little relation to advertised airflow. This is not a conclusion you would reach based on the science, but it's a fact.  This is because published ratings are usually at zero static pressure, which has no relation to how the fan will operate in your car. The fan you should be looking for would be rated at 1500 CFM, and would probably draw around 12-18 amps. Since there's not much electrical demand in a Diesel, you shouldn't have a problem with the alternator. In the worst case, it's easy enough to find a more powerful alternator.

- I did a write up for the Jaguar club on generic aftermarket fans, which might help: 
http://www.jcna.com/library/tech/tech0008.html

Mike Frank


At 07:31 PM 6/12/2004, Eric Ditwiler wrote:

> Anybody ever remove the stock fan and replace it with an electric one?