Forgive my ignorance, but I need someone to explain how the fan clutch works. I've been fighting with high running temperatures for a while now, and it's suddenly gotten worse. I've also started hearing a loud clacking from the front of the engine bay, so I believe my fan clutch is bad, but I'm not sure how to confirm before I shell out the cash for a new one. When I got the vehicle, all the fins in the fan clutch were full of crud. Like the PO spilled oil on it and then dropped it in the dirt. I removed a little piece of spring metal from the front, and a small copper pin fell out of it. After I cleaned the clutch as best I could, I tried to put it all back together, but the metal had to bend to go back into the assembly, so it didn't hold the pin in place. I believe the pin to be long gone. Did this doom my fan clutch from the start? Or am I completely off base here?

Yes, you need a new fan clutch now. They work based off of a temperature sensitive fluid with a little valve. I've attached the section of the service manual dealing with the fan clutch.

Attached Files

20-310.pdf (80.4 KB, 53 views)

"Is my fan clutch dead?"
Is this about a Farmall tractor? An Isetta? A skateboard? A glacier?

Probably a Mercedes diesel, considering the board and forum we are on. Also, the question is irrelevant.

A tractor? No. An Isetta could be fun, but a skateboard not so much. I do appreciate you thinking of my glacier. But yes, I'm dealing with a 1983 300D. I forgot this is a multi-car board, so apologies.

Thanks for the manual, nastala. Understanding how the clutch works definitely confirms my suspicions.

Glacier is close enough, describes a 300D nicely lol!

Yeah your fan is probably gone. The oil is probably the clutch oil, and that spring metal was probably the bimetallic spring that reacts to the heat to actuate lockup.

Take a rolled newspaper (remember what that is?) and try to stop the fan with it. If it stops, you need a new one.

If a 300D is a glacier, then a 240D must be a polar ice cap hahaha!

Thanks tyl604, that's a great test. Should the engine be up to running temp, or should it hold its own against the paper hot or cold?

As long as the fan is turning, you can do the test.

Well, let me think about that. When it heats up and the viscous fan clutch catches, the fan turns with strength. So I am not sure. Maybe it does need to be hot.

Can someone else chime in, please.

From the description you provided in post #1, it appears that you should forget about testing and focus on replacing your fan clutch.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I agree with tangifox007, it’s time to replace the clutch. It is oil filled, it sounds like the oil leaked out. The strip is bimetallic, if it fell out, it’s calibration is gone. And a bad clutch will rattle.

If you flick it hard with the engine off and it spins more than a half to 3/4 of a turn, it’s probably bad. If it doesn’t turn at all, it’s bad. It should feel stiff as gelatinous, like you are spinning it in oil.

Michael

I was going to say…. Pretty sure the fan clutch when engaged on my 5.9 Cummins Ram moves like 25k cfm and eats like 40HP. I would imagine a 300D would still be a non-trivial load. Be safe.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)