As summer came on, I noticed that the SDL temp gauge would venture to 100C and a little beyond in traffic with the AC on... and it's always on these days. I checked the archives and found instructions on refilling the clutch fan.

http://www.peachparts.com/shopforum/showthread.php?threadid=67800

There was all sorts of grime on the front face of the clutch when I pulled it off the engine so I figure fluid must have leaked out over 16 years. I used the 6000 centistoke stuff from Toyota crammed into the clutch with a medicine dose syringe. I've heard of clutches taking almost 2 bottles (~36ml) but satisfied myself with one bottle for now. There has to be some air for the clutch to disengage. Several methods are outlined. What worked for me is pushing on the syringe plunger until I feel the slightest resistance. Then pulling up on the plunger until I start to extract air. Bleed the syringe, rinse, repeat. It easily swallowed the contents of the Toyota 18ml bottle. I did this with the fan cold and static. I'd have to build a jig to be able to heat and spin the fan between squirts. Maybe a 928 fan comes off like a 617 fan.

Placebo or not, the temp gauge didn't go past 90C yesterday. I even punched it on the exit lane to get it nice and hot at the light at the bottom of the ramp. 90C.

I don't hear the fan kick in for a short while when I start the engine cold. My 450SEL used to do that. Maybe the 300SE did at some point.

The thread suggests that you can use STP oil treatment but from what I remember of my engine building days, that stuff won't come off whatever it touches.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD