I have a good suspicion that my fan clutch is bad. Before replacing it for about 120 bucks or so in parts is it a bad idea just to freeze it up so that it rotates at the same speed as the motor.

I drive my car like a grandma... rarely going over 3000 rpm.

Is there any real risk of damage if I do this.

Thanks again for your ideas


bob c

Dear Bob,

There's no risk at all if your fan clutch rotates at the same speed as the motor. Fan clutches are designed just to save some engine torque, and are only activated when needed (high temperature.)

However, if a fan clutch got disintegrated from its assembly, it will cause a mess in your engine compartment and possibly destroy
the radiator.

Eric

The Bob,

Yeah, you could try that but if you ever had to go to redline, no matter how distasteful you found it for your usual reasons, you might find the fan blades considered the experience so unpleasant they elected to leave the engine compartment. A clean exit is not likely supported by the arrangement of other equipment under the hood. So probability does not favor this as a permanent fix since it will tend to want to undo itself.

You will also find the mileage drops as the horsepower draw will be cubed with speed. Meaning if you spin it twice as fast you consume 8 times the power. At higher speeds this actually becomes a significant load. And it will make lots of noise at higher speeds. I am sure it has been done and the resulting compromise of noise and fuel efficiency loss tolerated if the temperature is being reduced. If a blade comes off the fan that compromise is not likely to be viewed in the same light.

Good luck, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Hi Mr. JimSmith:

Actually, the relationship between linear speed and kinetic energy
is E(k) = 1/2 * (m * v^2), where m is the mass of an object in motion and v is its speed. That is, the kinetic energy is proportional to the square (not cube as you mentioned) of the speed.

(This is the approximate formula based on Newtonian mechanics. If you want the exact formula from which this approximate formula
can be derived, here it is:

E(k) = m(0) * c^2 * {1/sqrt[1- (v/c)^2] - 1}

where m(0) is the rest mass of an object and c is the speed of light in vacuum (c=299,792,458 m/s). If you expand the exact formula in terms of Taylor series, you'll get the approximate one).

For rotational kinetic energy (as in this fan clutch case), the formula is E(RK) = 1/2 * ( I * O^2 ), where I is the rotational inertia (in kg*m^2) and O is the rotational velocity (in radians/s).
So the rotational kinetic energy is also proportional to the square (not cube) of the rotational velocity.

I have a c220 whose fan clutch does not work properly (always spinning fast) and I haven't replaced it yet. However, I have actually not observed any noticeable loss in fuel mileage with or without the bad fan clutch. The drag caused by the high spinning
fan clutch may not be big enough to affect engine performance.

Eric

I'm thinking that complaints of poor fuel economy with permanently engaged clutch fan would also be attributed to the engine running cool...hence the engine condition would also be affected over time, wouldn't it?

My $0.02.

friend had a fan blade come off his Chev at high rpm's not only did it penitrate the hood but also cut a hood reinforcement brace on it's way to freedom, he said he thought a first that some one had shot at his car with a high power rifle.........
I left a wrench under the hood in my long gone 71 240 Z Datsun it got in the fan ,bent a blade witch took out a couple of tubes in the raditor . I soldered the raditor and took the fan off after talking to mecanic that built and drove rally Datsuns.I did mostly hiway and back road driving with that car and it never overheated the engine felt more responsive and was much quiter....
William Rogers.....

Yup, Just gotta reply to any thread on fan clutches that involves rest mass and the speed of light, LOL. Isn't that called the Lorenz transformation? It was Einstein that proved it, but I thought it was Lorenz that came up with the formula.

Anyhoo: My fan clutch is DEFINATELY bad and I am going to do this sometime soon, but I was thinking the same thing about locking the clutch. The method I was going to try is wire it and then put duct tape over the wire. The thing I fear is if the wire/duct tape came loose, It'd tear up all of my radiator hoses and God knows what else. And that would leave me stranded....

Last weekend, I did a cooling service (degrease/clean/fill with Zerex coolant/new thermostat). What I found is that if your cooling system is working OK you don't get anywhere near 100 deg C while you are moving. I've seen 100 sometimes when stopped. Due to this, I'm in no hurry...

Moral of story: Get the rest of the cooling system working. Your car shouln't spend too much time with the fan on (if it's like mine).

p.s. Another thing I was thinking is that a flexalite fan would be a better choice anyway: no parts to break. But, at this point I'm going to just replace it and be done with it for a few years.

Sholin

__________________
What else, '73 MB 280 SEL (Lt Blue)
Daily driver: '84 190D 2.2 5 spd.

Eric,

A fan is a turbo machine and the output is measured in terms of flow and head. As speed increases both of these products increase. The rule for designing pumps, propellors and compressors is that power is consumed in a cubic relationship to speed. Torque is related by the square of speed. I think you were not calculating the effect on the air, but only the effect of the kinetic energy of the blades, which do perform as you described. However, the context of the discussion was horsepower drawn to run the fan at higher speeds, not the kinetic energy of the blades when they come off the hub. Jim

edit: Also, if there were no penalty in fuel economy to running the fan at the higher speeds, there would be no clutch. Also, as long as the thermostat is functioning properly, no matter how cold the water in the radiator gets the engine should run at its normal operating temperature. That is what the thermostat does, regulate temps. You might be in the mostly recirculation mode, but the engine will warm up like it does in the Winter. The only downside of system designed to run at engine speed all the time would be fuel consumption. The fan has to work at idle, meaning the fan has to move enough air through the radiator to enable the thermostat to successfully regulate temperatures. This sets the fan blade design. At speed you should be getting a huge boost in flow (the fan still develops about the same head but the initial conditions are now substantially different) from the car punching a hole in the air to move through. This makes the need for the fan to continue running under a higher load go away, thus the clutch. It is there to save fuel. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Bob,

If you're a bit resourceful, the fan can be chucked away and replaced with an electric one from a scrap-yard.

The easiest ones to fit are mounted to the front of the radiator. You just need to drill the side of the radiator and insert the temperature sensor (from the same scrap car) with a rubber grommet.

I've done this on most of my cars, when the Viscous unit packed-up. It has cost me a maximum of 10 quid.

__________________
Paul Gibbons
'93 320CE
'73 Jensen Interceptor (Resting)
Giant Full Sus Mountain Bike

Well, I guess we have figured out why 240d's are so slow.

1. They did not have any power to begin with.

2. They have fans bolted to their crank.

The Combo = Bugs on the rear glass.

Thanks for all the info.

It is nice to review all those physic formulas agian.


After considering the negative posible outcome. I may not do it after all.

My car never goes over 100 C and I replaced all the other cooling components last year.

I mght be fixing a problem that I dont have to


Thanks folks.


Bob C

Bob,

Don't get me wrong, I AM going to fix this. I also considered the electric fan idea: That would also make my R134 A/C system a little happier sitting at idle.

JimSmith: Yes, I agree the thermostat will regulate the car temp OK, but only up to a point. With no airflow over the radiator, you will run out of heat sheading capacity at a much lower air temp. AT this point your car goes from running perfectly OK to overheating and stranding you. That's why I need to fix it in the next 2 months or so: It'll be 100 deg F outside and I doubt that my car will idle properly without overheating then. So Although my temps are perfectly normal now, I don't want to get stranded in traffic somewhere.

Sholin

__________________
What else, '73 MB 280 SEL (Lt Blue)
Daily driver: '84 190D 2.2 5 spd.

Hey Bob, your "Interest" section reads like this: "Playing guitar and fixing stuff that is not broken."

Does this mean that you do NOT fix stuff that is broken (like this fan clutch case)? :-)

Eric

Einstein did not have to spend his time on fan math as he never owned or drove a car......
William Rogers.........

Yeah, Einstein rode a bicycle to work at the Institute for Advanced Studies of Princeton University until he died.

Eric