There is no way to test a fan clutch with engine off as the clutch requires to be spinning to work, When the engine stops the oil pools on the bottom side of the vertical clutch and becomes heavy (we assume the clutch is working) - as soon as the oil distributes out the clutch decouples and freewheels - it will only work again when the bimetal spring lifts up from heat and allows oil to run to the outer perimeter of the clutch.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Here's what the fan looks like after the drive home. Perhaps it's not hot enough.

And right after the engine is stopped. It's actually lots stiffer in the morning.

Next I'll try stopping the engine right at the top of a hill to see how fast it comes down from a spin.


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1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

Looks normal, unless your temp gauge is reading 100C, your fan clutch will likely not be engaged and it will spin fairly freely.

In the morning spin the fan and see if you can get it to spin more than 1/2 turn cold, mine (with 300k miles) will only spin around 90* and stop.

Also, I drove mine yesterday, listened for the "roar", there is none. However I thought about it as I drove, and realized that there won't be at idle, if you rev the engine to 1000rpm-1200rpm in the first seconds after starting cold then perhaps there will.

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Gone to the dark side

- Jeff

Even when air temps / motor temps are cool my 603 fan roars until 2,000 rpm (2k consistently > 20 sec) then cuts out.

With fully warmed motor and ambient temps over 100F, even at 3,000 or so rpms, the fan occasionally roars up till motor cools. Usually see it on long uphill grades.

I kind of like that it stays engaged <2k rpms even in milder climates. Seems to keep the motor cool and helps with the AC.

Don't mind the related energy cost (hp & fuel)

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1986 300SDL 440,xxx

Sorry to ressurect this thread, but zu!, what was the conclusion?

I'm trying to sort out my '87 300D running a bit warmer than I'd like. I just replaced my fan clutch, but it seems like the new one might be worse than the old one! I don't hear any roar on startup, but I never did with the old clutch either. What concerns me is how much the fan freewheels after the engine is shut off when it's hot (90-95*+). It'll go a few full revolutions, maybe more. The old one would stop in less than a full revolution.

My temps are fine (~90*) at speed, even with the A/C on, but at a stoplight they start creeping up and touching the 100* line, even though it's only been about 75*F here. Did I get a bad new fan clutch? Are my temps actually fine and I'm just being paranoid?

Check your freon, if it is low then the pressure will not turn on the electric fan. With the electric fan running / cycling at a stoplight it should stay cooler (or so has been my experience).

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Gone to the dark side

- Jeff

I got a bad one first time around, so it is possible. Have you tried changing to the red switch? I never heard my electric fan come on until I changed that one out. Then once on a long uphill drive on a hot day, I had to get out of the car to help a little old lady and I heard her roar...the TD, that is.

My fan free wheels too on stop , but I've seen a difference in slow traffic temps with the new clutch. It definitely made a difference.

I'm on the brink of testing a coolant additive that's supposed to cool engines (including diesels!) more efficiently. If it works, I'll report back. With our heads, I think we can use all the help we can get!


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1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

I guess I should clarify that my electric fan DOES work. It comes on fine with the A/C on, but it's the original temp switch. Since it doesn't come on until ~110 I haven't been letting it get high enough to trigger it. Jumping the switch, it works fine.

My concern is with the viscous clutch. I'm going to try a different one and see if it works any better. At what temperature should the clutch engage? I thought my old one was probably faulty, although it seemed to pass the "tests" (try stopping it with a newspaper, how many revolutions at hot shut-off, some resistance when cold). I decided to replace it anyway (my old thermostat seemed to pass tests too, but with a new one the car runs ~5* cooler), but the new one now FAILS all of those tests. I can stop the fan easily even when the engine temp is ~95*, and it spins a few revolutions after a shutoff when warmed up.