Removing viscous fan to reduce engine load
 

Hi all,

I have noticed on my E300 that it has the clutched (guessing viscous) cooling fan attached to the front of the engine. This is in addition to the 2 large electric cooling fans on the front of the radiator as well.

I was just wondering if anyone had removed the stock fan and just used the normal electric fans (much like all modern cars). Just wondering if anyone had as I am sure that having the fan attached to the front of the engine would increase the engine load, much like the AC pump when its activated.

Are there any issues in removing the stock fan at all?

I haven't done this but it is a viable solution especially in a cooler climate. The engine driven rad fan on many cars seems to stay engaged at some % to keep air flowing through the AC condenser. For the aux fan, I'd use a lower AC pressure switch / lower coolant temp turn on point to change the fan from aux to primary as standard aux operation is more of a helping hand.

As a test you could remove the fan, add a switch to trigger the fan relay then drive around. The switch will allow you to trigger the fan if temps get too high. At road speed the fan does not do much so in town is where watching temps becomes more critical.

I can share some data on this learned through experience when I hit a curb stop and broke the fan on my W210.

It happened in the hot summer here, it was in the high 80s/30 C.

Engine ran about 15 degrees hotter, usually I am at 80C and it was running at close to 100.

A/C performance was terrible. The engine driven fan is needed to pull air through the condenser foe effective heat transfer.

Also the electric front fan control on the W210 is electronic, there is a PWM? controller up front. Not the simple 2 relay and resistor setup like on the 124.

I've done it on my om603 but not the om606 yet. There's a couple of issues. First the 2 pusher fans in front of the radiator are actually just 1 electric fan with the second just being driven by a belt from the first. When you spin one by hand they both turn. Replacing the second belt driven fan with an electric is impossible because the mount is different event tho the fans look the same (thanks Mercedes)

The pusher fans are very inefficient. With the engine off and key turned to position 2 press and hold the 2 AUTO buttons on the climate control for 10 sec. This will turn on the electric fan. Once running check the flow rare through the radiator. The pusher fans are weak and leak a lot of air around the perimeterm. I don't think they're powerful enough to cool the engine on their own. For the system to be effective you would need to replace the pusher fans with something more powerful.

On my om603 I have 1 electric pusher fan and 1 electric puller fan running of the same circuit with a temperature switch on the engine. On both cars space is very limited between the radiator and the engine. You can only fit a relatively weak electric puller fan. Something like the popular Volvo fan (used on a lot of electric swaps) won't fit.

The pwm control is built into the climate control and a separate device on the firewall. The fan is indeed just a simple fan. It could be replaced by any other simple fan. The trick is switching it on earlier at a lower temp so it doesn't run hot.

Keep in mind also that the load removed from the engine by eliminating the fan will simply be transferred to the alternator to run an electric fan(s).

Don't forget the load on the viscous fan is always there while the engine is running but not so with the electric fan, which is on only when the set point of the fan switch is exceeded. The electric fan will be more efficient.

I'd be interested to see how it works out. I had a hose hang up the fan on my 602 fan over the winter. It is literally fingertip torque unless the fan is hot because the motor is, the thermostat is open and cooling is required.

MY feeling is that the a lossy alternator and a lossy motor will be more of a drag on the motor than a decoupled fan.

You will encounter the usual reactionary 'billions were spent making it that way' pushback, but maintain an open mind an see how it works out.

It's the first thing I remove as not really needed here in UK.

Only once in the last 6 years or so has the temp risen above 85c, that was in a long jam with outside temps of 27/28c.

If you have a good ratio of anti-freeze it will also help keep engine cooler during summer months. Winter it heats up quicker and I guess saves a few pennies on fuel.

On the w210 bit tricky to remove though, getting an alien key on the bolt with little room is fiddly.

Hmmn, is the 602 fan clutch different than the 617? Per 617 FSM, the viscous clutch is fully engaged for a few minutes from a cold start until centrifugal action spins away the glycerin and unlocks it. If the 602 clutch works the same way, then something is not right with yours.

Owing to today actually having some sun out and I needed to do some test drives I thought I would see what the temperatures got to.

Using the hidden menu within the climate control module I pulled up the coolent temperatures, I don't really ever see this above around 80ish, sitting in traffic it got up to around 92-93c. I wasn't sure which thermostat I had fitted but it should be the higher temperature one as its the standard turbo engine.

This makes me think of 2 things:

1. The viscous fan is doing an OK job at keeping the temps in check
2. My 2 front pusher fans aren't working!

I will keep and eye on the temperatures via the console and see what it usually gets to on cruise etc. I will also see what it gets during drag runs but I think from the large volume of coolent in the system it shouldn't rise too much.

I am tempted to fit a small electric fan on one side though and have it switched so that I always have the option to have extra cooling.

The aux fans only come on when AC high side pressures are higher than normal and possible if coolant temps get higher than normal.

Ran my W124/OM603 with the fan removed and a slim electric puller fan in its place. I could absolutely feel more power than with it lugging that mechanical fan around. If i recall, I gained 1-2mpg also. I also tried with just the pusher fan wired on and nothing else, it works ok unless its pretty hot out and the a/c isn't as cool. The pusher fans suck to be frank. I will be using a nice all aluminum radiator and a good puller fan once I drop my OM606 in to the car. No more viscous fans for me. And if you look at new cars, most are ditching the viscous fans and going electric with PWM controllers. BMW has gone this way, I bet all newer Mercedes are too. Its the way of the future. You can buy an aftermarket or create a PWM fan controller now too. I will use one of these two options and the biggest fan that will fit.

PWM Controller : PWM Fan Controller, Push In Probe

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Press and hold the 2 AUTO buttons on the climate control unit for 10 sec. The aux fans should turn on if they are functional.

On the transferring load to the alternator. The advantage to an electric fan is the fan shuts off completely when not needed, a viscous fan does not and still drags. Some cars use a electric fan clutch to get around this. ( Chevy Trailblazer for one )

If in cooler climates think about using a rad blind once fan removed.

Rad blind experiment - MBClub UK - Bringing together Mercedes Enthusiasts