No I understand your point completely and I definitely plan to check the other parts of the system to ensure everything is in working order. I just wanted to do the fan clutch as something extra that's all

You are correct, but the 300 turbo motor puts a lot more heat into the radiator when it is making power. The clutch sits right behind the radiator. On a 240d making about half the power of a 300 I doubt there would ever be a time it will lock in at speed if all other cooling components are working correctly.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I wonder what it'll be in the end .

Me, I'd do another Citric Acid flush before anything else, 6 years is a long time .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

That's cool, I hope you get it all sorted out!

A thought… the OP’s original set up is a fixed fan always spinning 100 per cent.
People have said no need to increase capacity of fan by going to 9 blade viscous clutch, stock system is fine, you will loose MPG, the 4 cylinder puts out nowhere near the heat of a 617 turbo into the cooling system etc.
It’s all true.

I wonder this: Going down the road on an average day is there less of a load on the motor spinning a 9 blade viscous clutch than the stock fixed fan? I think yes. Less load=better MPG & power to wheels.
Will the 616 get hot enough to cause the 617 turbo fan clutch’s bi-metal spring to engage the fan clutch. Probably only in extreme outside temps and high load.

I think it would be a good upgrade. Not needed unless things get bad then a fan designed for a 3 liter turbo diesel will pull more air through the radiator. A number of times I have driven West out of Death Valley in 116-119F temps which is a bunch of steep uphill miles, radiator water refill tanks every so often. I’ll bet in that kind of situation the 9 blade will fully engage and cool better that the stock fan.
And, going down the road on an average day it’s less of a load than the stock fan.
All in all, a good upgrade if you want to do it.
Wish I was in Death Valley right now instead of Manhattan, it’s really bad here with this virus. This is the new death valley.
Stay safe.

FWIW, I've driven Death Valley in my 1982 240D Slush box many times, I always have the windows closed and the A/C set on refrigerate , even going over daylight pass and it's always cool and comfy, the stock cooling system has no difficulties .

I agree, lighter, nylon fans and clutches are nice up grades but these cars were designed to do TAXI DUTY IN THE MIDDLE EAST so much ballyhoo about nothing , just maintain it properly and do the citric acid flush every few years .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

hah hah, yes!

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Its been months since I posted on this old thread, but I finally upgraded to the fan clutch from a 300sd and there is some improvement. The amount of airflow moving through the radiator at idle is substantial and when you race the engine up the fan revs high too and it sounds like a jet engine a little bit. Not only that but the engine felt like it had a little bit more pickup to it, like it was more responsive. I had a big smile on my face revving the engine through the gears and hearing that diesel goodness combined with a jet engine like-sounding fan at high rpm. I would recommend doing this because of the increase in pickup and higher cfm's of air being moved through the radiator and engine bay. But this is not something that is drastically going to affect cooling system performance. Check the main components first and troubleshoot those before doing modifications like I am. Another problem I fixed recently was my temp gauge wire was shorting out from cracks in the insulation by the block and it caused my temp gauge to read higher than usual so I had to run a new wire and replaced the temp sender which made a difference. The car now stays around 85 degrees C all the time and takes awhile to get past 80 degrees C with the heat on.

Also I've heard of people putting coolant additives in the cooling system to lower the conductivity of the coolant in the block any thoughts on this? And no I do not plan to go out and buy that royal purple ice stuff after reading the horror stories on this website.

It sounds like your fan clutch is locked up. They'll be engaged when you first start the engine due to the fluid pooling, but should quickly unlock on a cold engine. Once the clutch unlocks, the fan speed won't ever rise much above it's idle speed regardless of engine speed until the air hitting the bimetal element in the center of the fan clutch reaches its operating temperature (meaning the radiator isn't keeping up with natural draft). Then, the clutch will engage, but they're designed to start slipping around 3000ish RPM, so it shouldn't sound like a "siren" at any point if it's working correctly.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]