1984 300DT. I suspect my fan clutch is bad. Is there a test I can perform to find out?

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There is a way to tell but I can't remember it. That info may be in the repair links.

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84 300D, 82 Volvo 244Gl Diesel

There is some indication from these threads that when the fan clutch does not work when you are have been running and come back to idle the temp at idle is higher then normal.

New 1985 300D overheating. Or is it?

Hot but not overheating

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84 300D, 82 Volvo 244Gl Diesel

It sounds like this only not as bad........

https://www.youtube.com/watch?v=_fmmKghdhC0

If it sounds like that, it's junk. Not sure why you'd even question it as a replacement item if you've already identified it's rattling and clattering.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

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

If the engine temp gauge honestly reads over 100*C at idle and you don’t hear the clutch fan roaring louder than the aux fan, the clutch is shot or isn’t being triggered.

There’s more than just the clutch fan. The air reaching the fan has to be hot enough to trigger the clutch. Make sure airflow to the fan clutch isn’t obstructed.

The fan has to be spinning between idle and something like 2500 engine rpm. Below that “clutch fluid” isn’t circulating. Above that the fan is supposed to freewheel.

Winter climate makes it more difficult to test the fan.

When you install a new clutch, one thing you’ll notice is a roar for a few seconds after starting a cold engine. It goes for up to half a minute as I recall as clutch fluid is distributed. If you don’t hear that roar on a cold engine, you might still hear that roar on a hot day, but the clutch is getting tired.

Sixto
98 E320s sedan and wagon
02 C320 wagon

I may be all wet but here is what I remember. I have a 1981 300SD and noticed that it was running slightly hotter than usual - running about 100 C and has always run about 90 C. At that point I did not even know what a viscous fan is.

Got advice from the forum - let the engine get good and hot, watch the fan while someone turns the engine off. If the fan does not stop immediately, the viscous fan clutch is bad/going bad.

My fan did not stop immediately and I replaced the viscous fan clutch. Guess it took maybe 30 minutes. Problem went away immediately. Do not remember it being very expensive. $36 at Pep Boys; Pelican was higher.

OK - finally found the post. It was from Diseasel300 and he was exactly right:

"Your car has a viscous clutch, you had to remove it to change the water pump. It's the finned disc that the fan is attached to. A general guideline is that when the engine is hot, the fan should stop very quickly if not immediately when the engine is stopped. If it keeps spinning, or spins several revolutions, it's time for a new one. They're a common failure item."

Ran the car until it got good and hot, fortunately temps stayed below normal for the engine. Had a friend turn off the engine while I looked at the fan. After engine shut down, the fan spun for about 10- 20 seconds. So......looks like a new fan clutch is on the menu.....

Thank you to everyone who weighed in on this one.

Easy fix. Good luck.

Even when cold the clutch shouldn't freewheel for 10-20 seconds. Maybe 2-3 seconds at most. That clutch was dead long ago. Time for Last Rites and a fresh replacement!

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

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